HTM Electrical services supply and distribution.pdf

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Department of Health / Estates and Facilities Division

HTM 06-01, Part A

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HTMs 2007, 2011 and 2014

Oct 2006

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Department of Health libraries, House of Commons library,

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Estates and Facilities,

Health Technical Memorandum 06-01, Part A, provides guidance

on the design, installation and testing of all fixed wiring and

integral electrical equipment used for electrical services within

healthcare premises.

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Health Technical Memorandum 06-01, Part A: 'Electrical services

supply and distribution'

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Electrical servicesHealth Technical Memorandum06-01: Electrical services supply and

distribution

Part A: Design considerations


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Electrical services HTM 06-01 Electrical services supply and distribution: Part A Design considerat

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HTM 07

Environment &Sustainability

HTM 08

SpecialistServices

HTM 01

Decontamination

HTM 02

MedicaGases

P li i d

INTERNAT

IONAL&

EUROPEANSTA

NDARDS

IND

S

INDU

STRY STANDARD

S

HEALT

H SPEC IF IC DOCUM

ENTS

HEA

LT HTM 00


Health Technical Memorandum 03Heating and ventilation systems

Health Technical Memorandum 04Water systems

Health Technical Memorandum 05Fire safety

Health Technical Memorandum 06

Electrical servicesHealth Technical Memorandum 07

Environment and sustainability

Health Technical Memorandum 08Specialist services

Some subject areas may be further developed into topicsshown as -01, -02 etc and further referenced into Parts A,

B etc.Example: Health Technical Memorandum 06-02 Part Awill represent:

Electrical Services Electrical safvoltage systems

In a similar way Health Technicawill simply represent:

Environment and Sustainability

All Health Technical Memorandinitial document Health Technic

which embraces the managemenfrom previous documents and exissues.

Some variation in style and structopic and approach of the differegroups.

DH Estates and Facilities Divisio

the contribution made by profesengineering consultants, healthcNHS staff who have contributed

Figure 2 Engineering guidance


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Health Technical Memorandum 06-01 Electricalservices supply and distribution replaces HealthTechnical Memorandum 2007 Electrical servicessupply and distribution and Health TechnicalMemorandum 2011 Emergency electrical services,and absorbs Health Technical Memorandum 2014 Abatement of electrical interference.

This part (Part A) provides guidance for all works on thefixed wiring and integral electrical equipment used forelectrical services within healthcare premises.

This document should be usedesign work ranging from a nmodifying an existing final sueach section will depend on thworks.

It provides guidance to managon how European and British

electrical safety such as the IEBS 7671, the Building RegulaElectricity at Work Regulationtheir duty of care in relation t

Work etc Act 1974.

Executive summary


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Main working group

Owen Cusack Northumbria Healthcare NHS Trust

Peter Desforges Develop

Alan Gascoine Mayday Hospital

Ian Hawthorn Sandwell General Hospital

Chris Holme Department of Health Estates and FacilitiesJim Mellish Skanska UK PLC

John Murray Bender UK

Nigel Porter Welsh Health Estates

Mike Ralph Great Ormond Street Hospital

Steve Wilson Faber Maunsell AECOM

Subject working groups

Switchgear and Protection Schneider Electric

Containment Systems

Dick Shelly Skanska UK PLC

Andrew Galloway Great Ormond Street Hospital

Isolated Power SuppliesJohn Murray Bender UK

Electromagnetic Compatibility

Alwyn Finney ERA Technology

Acknowledgements


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Contents

PrefaceExecutive summary

AcknowledgementsChapter 1 Scope of Health Technical Memorandum 06-01

Abbreviations and definitionsChapter 2 Introduction

OverviewHow to read this Health Technical Memorandum

Chapter 3 Initial considerations Sources of supplyResilienceEssential/non-essential suppliesPrimary sources of supplySecondary main sources of supply generationTariff negotiations and private generationSupply voltagesDesign of installations for growth and change

Assessment of existing electrical systemsGreenfield siteNew-build on existing siteNew equipment on existing site

Load profileDiversity factorsConsideration for EMC requirements

Roles and responsibilitiesAccess for maintenanceCommissioning procedures

Connection to the DNOConnection to the healthcare site networkSupply from the DNO


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Category 2 Building services safety and securityCategory 3 Building services environmental controlCategory 4 Medical support services

Electrical infrastructureResilienceElectrical infrastructure system selection

Chapter 5 Power quality Power factor correction

Located at the intake pointLocated at sub-main distribution boardsLocated on the electrical equipment

HarmonicsLocated at the intake pointLocated at sub-main distribution boardsLocated on the electrical equipment

Voltage surge protectionChapter 6 Distribution strategy

Design for resilienceSupply connectionsRisk of transformer failuresRisk of generator failuresOther reasons for failure of electricity supply

Distribution system high voltageHV network one radial circuit with one substation onlyHV network one radial circuit with three substations

HV network three radial circuits each with one substationHV ring network ring with four substations

Primary and secondary distribution systemsPrimary supply unified infrastructurePrimary and secondary supply unified and segregated infrastrPrimary and secondary supply unified and dual-unified infraDual primary and dual secondary supply unified and dual-unDual primary and dual HV secondary supply dual-unified in

Dual primary and dual LV secondary supply dual-unified infFinal circuits

Fixed equipmentPower outletsLighting circuits

Chapter 7 Primary power distribution centres


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LV switchroomsLocationConstruction

Access and egressLayoutFire precautionsEnvironmental requirementsEquipment and notices required to be provided

Chapter 8 Secondary power centres and plant Secondary power general arrangements

Photovoltaic power secondary power sourceWind turbine power source

General secondary power plant locationEssential power capacityEssential and emergency power provisionStandby generators

Design criteria

Component partsGenerator configuration

Mobile plug-in generator island operationGenerator(s) in island operationGenerator(s) operating in parallel with PES

LV generators feeding HV ring mainGenerator control

Generating set management

Multi-set operationMains returnComputerised load management of generators

Standards and referencesGenerator enginesBatteries and battery chargingFuel and fuel storageExhaust systems

Environmental considerationsChapter 9 Protection and switchgear

High-voltage switchgearWithdrawable unitsSemi-withdrawable unitsFixed-pattern units


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Generator protectionLow-voltage switchboards

Form 2Form 3Form 4Motor control centre (MCC)Final distribution boards and consumer units

Low-voltage protection devicesSwitch

DisconnectorFuseCircuit breaker

Low-voltage busbar sectionsDiscrimination of protective devices

Discrimination with HBC/HBC fusesDiscrimination with MCB/MCCBDiscrimination with MCB/fuse

Discrimination with RCDsAutomatic load management of switchgear (HV, LV)

Chapter 10 Tertiary power supplies Batteries for uninterruptible power supplies

Battery typeBattery lifeBattery arrangementsBattery autonomy

Batteries for inverter unitsBattery typeBattery lifeBattery arrangementsBattery autonomy

Generator batteriesBattery typeBattery life

Battery autonomyChapter 11 Electromagnetic compatibility

StandardsProcurement requirementsEMC phenomena

Standards and levels


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Medical IT

Protected extra low voltage systemsSeparated extra low voltage systems

Chapter 13 Earthing High-voltage earthing methods

High-voltage network cablesHigh-voltage generator earths

Low-voltage main earthing methodsLow-voltage generator earths

Switchroom earthsEarths for radiographic roomsMedical IT or isolated power supply earths

MicroshockCircuit protective conductorsFunctional earthMonitored earthing systemsLightning protection

Lightning protection system componentsIonised fields

Chapter 14 Containment Trenches, service tunnels and ductsLadder rack tray basketryTrunking conduitsPreformed wiring containment

Layout considerations

Fire precautionsRemodelling and extensionsCircuit segregationAccess for maintenanceSuitable locations

Chapter 15 Cable and busbar types High-voltage distributionLow-voltage distribution

Cable identificationBusbar distribution

Control alarm and communication cablesControl communication and non-fire-alarm cablesInformation technology cablesFire alarm cables


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IPS communication

ResilienceThe patient environmentIPS low-power circuits

General low-power circuitsSocket-outlets/connection unitsSockets for special locationsSockets for operating theatre suitesSocket for mobile X-ray units

Spark-proof socketsNumber of outlets per final circuit

Fixed equipmentSupplies to external buildingsTemporary suppliesConnections for mobile trailer unitsGeneral lightingTheatre operating lamps

Examination lamps lightingEmergency escape lightingStandby lightingFire alarm, security circuits and critical alarmsBEMS communication and control wiring systems

Chapter 17 Validation and commissioning Validation of specific plant

Generators and CHP plant

Uninterruptible power suppliesIsolated power supplies

Fixed wiring distribution, switchgear and protectionRecords to be keptAs-installed drawingsBuilding logbook

Appendix 1 Maximum interruption times to the primary supply Appendix 2 Sample test record sheets

Appendix 3 Drawing symbols References

Acts and RegulationsBritish, European and International StandardsDepartment of Health publicationsMiscellaneouspublications


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1.1 Health Technical Memorandum 06-01 Electricalservices supply and distribution replaces HealthTechnical Memorandum 2007 Electrical servicessupply and distribution and Health TechnicalMemorandum 2011 Emergency electricalservices, and absorbs Health TechnicalMemorandum 2014 Abatement of electricalinterference.

1.2 This part (Part A) provides guidance for allworks on the fixed wiring and integral electricalequipment used for electrical services withinhealthcare premises. The document should be usedfor all forms of electrical design work ranging froma new greenfield site to modifying an existing finalsubcircuit.

1.3 This document provides guidance to managers ofhealthcare premises on how European and BritishStandards relating to electrical safety such as theIEE Wiring Regulations BS 7671, the BuildingRegulations 2000 and the Electricity at WorkRegulations 1989 can be used to fulfil their duty ofcare in relation to the Health and Safety at Worketc Act 1974.

1.4 The policies and principles of all engineeringservices are described in Health TechnicalMemorandum 00 Policies and principles, whichshould be read in conjunction with this document.

Abb i ti d d fi iti

BSRIA: Building Services ResAssociation

CCM: CIBSE commissioning

CCTV: closed-circuit televisio

CDM: Construction Design aRegulations

CE: European ConformityCENELEC: The European CElectrotechnical Standardizati

CHP: combined heat and pow

CIBSE: Chartered Institute oEngineers

CPC: circuit protective conduCT: current transformer

DB: distribution board

DBU: distribution unit

dc: direct current

DNO: distribution network o

DRUPS: diesel rotary uninter

DTC: diagnostic and treatme

EC: European Community

ECG: electrocardiogram

1 Scope of Health Technical Memora06-01


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ESD: electrostatic discharge

ETSI: European Telecommunications Standards Institute

EU: European Union

FL: full load

GRP: Glass-reinforced plastic

GSM: global system for mobile communication

HBC: high breaking capacityHBN: Health Building Note

HDU: high dependency unit

HFN: Health Facilities Note

HGN: Health Guidance Note

HRC: high rupturing capacity

HV: high voltage (11 kV)

HVAC: heating ventilation and air-conditioning

ICU: intensive care unit

IDMT: inverse definite minimum time

IEC: International Electrotechnical Commission

IEE: Institute of Electrical EngineeringIGBT: Insulated-gate bipolar transistor

IM&T: information management and technology

IMD: insulation monitoring device

IP: ingress protection (rating)

IPS: isolated power supplies (also known as medical IT)

ISO: International Standards Organisation

ISS: intake substation

IT: impedance terra earthed (derived from an isolatedpower supply)

MCCB: moulded-case circuit br

MD: maximum demand

Medical IT: medical impedance known as IPS

MEIGaN: Medical Electrical InsNotes

MET: main earth terminal

MRI: magnetic resonance imagi

NEAT: NHS Environmental Ass

NHS: National Health Service

OCB: oil circuit breaker

OJEC/OJEU: Official Journal oCommunity/Union

ONAN: oil natural circulation, a

PEC: protective earth conductor

PEI: primary electrical infrastruc

PELV: protected extra LV

PES: public electrical supply

PET: protective earth terminalPF: power factor

PFC: power factor correction

PFI: Private Finance Initiative

PPE: personal protective equipm

PPS: primary power source

PSCC: prospective short-circuit

PV: photovoltaic cell

PVC: polyvinyl chloride

RCBO: residual current breaker


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1 Scope of Health

SPS: secondary power source

TETRA: trans-European trunked radio access

TFL: time fuses links may also be referred to as tlf time-lag fuses

THD: total harmonic distortion

TN-C: combined neutral and earth throughout theelectrical distribution system

TN-C-S: neutral and earth is combined at point ofsupply and separate throughout the electrical installation

TN-S: separate neutral and earth throughout theelectrical system

TP & N: three-phase and neutral

TPS: tertiary power supply

UMTS: universal mobile telecommunications serviceUPS: uninterruptible power supply

VRLA: valve regulated lead acid (battery)

VT: voltage transformer

XLPE: cross-linked polyethylene

Applied part: part of a medical electrical device which innormal use necessarily comes into physical contact withthe patient for the device to perform its function

or

can be brought into contact with the patient

or

needs to be touched by the patient.

Authorised Person (HV): a person appointed to takeresponsibility for the effective management of the safetyguidance given in Health Technical Memorandum 06-03

correct and in a safe manner. T

direct employee of the healthcEssential: any part of the elecfinal circuits that can be autombetween either the primary or

Medical electrical equipmenintended to diagnose, treat or medical supervision which wil

contact with the patient, transpatient, or detect such energy Note: equipment is not covereMemorandum. The MedicineRegulatory Agency (MHRA) which is responsible for ensurworks and is acceptably safe.

Medical IT (IPS): IT electricrequirements for medical instainclude a monitoring device toof IMD connections, insulatiohigh temperature.

Medical location: location indiagnosic treatment (includinpatient under medical supervi

Group 0Medical location wintended to be used.

Group 1 Medical location welectrical supply is not a rislocation is part of a Group

Group 2Medical location welectrical supply can cause

Note: discontinuity means apower supply (seeMEIGaN).

MEIGaN: Medical Electrical Note published by MHRA.


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Point of use: Electrical distribution points where

electrical equipment may be connected. This may be anaccessory or isolator etc.

Protected extra LV: a SELV system that is earthed at onepoint only. Additional protection against direct contact isachieved by barriers and/or enclosures. Alternatively theinsulation will have a withstand test voltage of 500 Vdc for 60 seconds.

Residual risk: a risk that has not been fully mitigated bythe design process.

Segregated distribution: an electrical distribution thatincludes separated primary and secondary circuits not ofequal size or capacity. The secondary circuits are the onlycircuits that are supported by the standby power system.

Separated extra LV: an LV system (normally not

exceeding 50 V ac or 120 V ripple-free dc) derived from asafety source such as an isolating transformer to BS EN61558-1:1998 and BS EN 61558-2.

Single point of failure: a connection point (other than apoint of use) where any upstream single fault will causethe loss of supply to the downstream parts of thedistribution.

Stakeholder: a person (or organ

interest (not necessary pecuniaryquality and provision at healthcastakeholders will normally be an healthcare organisation.

Tertiary power supply: a third sthe primary and secondary supplof an UPS or battery system.

Unified distribution: primary ((essential) circuits combined as ocommon electrical distribution o

Where the secondary power sour100% capacity of the primary poautomatic devices will be requireessential circuits whenever the prnot available.



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Overview

2.1 Health Technical Memoranda 2007, 2011 and2014 have been superseded and combined into onedocument: Health Technical Memorandum 06-01.

2.2 Health Technical Memorandum 06-01 Part Aaddresses design considerations for the electricalservices supply and distribution within anyhealthcare facility. Part B addresses the operationalmanagement and maintenance of the electricalservices supply and distribution within anyhealthcare facility. Both parts provide bestpractice guidance on the design and operationalmanagement of electrical services within healthcarepremises.

2.3 Throughout this document, the following voltagesare used (see BS 7671:2001 for the defined voltagebands):

Extra low voltage 50 V ac or 120 V ripple-free dc

Separated extra lowvoltage (SELV)

50 V ac or 120 V ripple-free dc

Protected extra low

voltage (PELV)

50 V ac or 120 V ripple-free dc

Low voltage 230 V phase to neutral, phase to earthor line-to-line (medical IT)

400 V phase to phase

High voltage 11,000 V phase to phase

from the various distcircuits and point of

Chapter 3provides guidanceconsidered when planning a of the electrical services.Chapter 4explains how the be assessed to minimise the r

the consequential impact to phealthcare premises. The chaconcept of clinical risk in termof a department within the hchapter also considers the busimilar manner. The chapter may be used in the evaluationstrategy.Chapter 5defines the requirelectrical supply.Chapter 6describes the techprovide an appropriate resiliehealthcare facility (or part wiChapter 7 describes the physswitchrooms, their construct

environmental requirements.Chapter 8continues the desthat may be used for alternatpower supplies.Chapter 9provides the detaiequipment that will be found

2 Introduction


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Chapter 13describes the full earth systems to be used.The chapter has a section for HV, LV, and switchroomearths. In addition, the specific requirements forisolated power supplies, earthing radiographic roomsand circuits with high leakage currents are discussed.The method of providing earth monitoring systems toBS 4444:1989 for mobile trailer units is also consideredin the guidance. The chapter concludes with therequirements for lightning protection systems.Chapters 14and15describe the various cable typesand the respective methods of installing them inhealthcare premises.Chapter 16 describes the various final circuits,including uninterruptible power supplies, isolatedpower supplies, fixed equipment temporary suppliesand alarm circuits.

Chapter 17 provides designers and stakeholders withan insight into the validation and commissioning testsrequired before a new installation may be signed offand formally accepted.Appendices andReferencescan be found at the end.

How to read this HealtMemorandum

2.5 This document has been wformat. The design processlikely to follow a similar plconstruction order to that

2.6 It is recommended that dereviewChapter 4 as well asprojects.

2.7 Designers and stakeholderchapter in relation to the nproject.



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3.1 This chapter introduces the design element of thedocument. The intent is to assist designers andstakeholders to develop the design of electricalnetworks for new builds, but equally it appliesto modifications to existing installations. Somesections of this chapter can be addressed prior to orduring the outline design stage, but all sections canbe addressed before the detailed electrical design

stage.

Sources of supply

3.2 All healthcare premises require an electricalconnection to the public electrical supply (PES),which will be provided and operated by thedistribution network operator (DNO). Electrical

supplies to large healthcare premises are mainlyat 11 kV (high voltage), while smaller healthcarepremises may be supplied at 400 V (low voltage).The supply frequency at both voltage levels willbe 50 Hz (see the Electricity Safety, Quality andContinuity Regulations 2002 for further details).

Within this Health Technical Memorandum, theconnection to the PES will be referred to as the

primary source of supply. Any embeddedgenerating plant and/or combined heat and power(CHP) plant can be used as the primary sourceof supply, provided appropriate measures forresilience, maintenance and safety have beenincluded.

b. tertiary source of sup(v) uninterruptible

rotary or silent

(vi) UPS static;

(vii) battery packs.

3.4 Adequate stocks of the f

generators and/or CHPThe fuel for wind turbinphotovoltaic systems (soreadily available at the otherefore these sources oconsidered as essential pbatteries as a power souautonomy dependent on

and battery supplies shoshort-term measure. Thused as the secondary soappropriate measures fomaintenance and safety the embedded sources oit may be less viable to pconnection than it is to

secondary power suppligenerators.

Resilience

3.5 Large healthcare premis

3 Initial considerations


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Essential/non-essential supplies

3.7 When planning for new installations, the optionof segregated non-essential and essential electricalsystems or a unified electrical system (that is,duplex or simplex) should be evaluated.

3.8 The need for more essential supplies increases thedemand on the standby system. Electrical suppliesin the healthcare sector are growing at a rate of

between 3% and 6% year on year. A suitablephilosophy should be agreed with estates staff toreflect this growth before sizing the standby plantand distribution strategy.

3.9 A risk-orientated approach should be adopted,and different categories of the essential and non-essential load identified to assign appropriate

standby provision (historically, it has beencustomary to have a discrete segregated essential/non-essential service combination). For clinicalareas, there should be 100% essential loadprovision. A segregated duplicated essential systemcould be used to overcome the inherent single-faultbreakdown potential. This would also facilitate theoperational opportunity to test and periodically

validate electrical installations.3.10 The provision of two segregated systems, each of

smaller power capacity, should be balanced againsthaving one larger unified power system in termsof economics and reliability in emergencies. Theavailability of the distribution and final subcircuitsfor testing, validation and upgrading of systemsshould also be taken into consideration.

3.11 In systems that employ a segregated duplicatedessential service, thought should given to the spaceneeded for separate feeders, independent risers andstand-alone distribution board (DB) cupboards soas to reinforce the system resilience. This will help

h l l f il ill i

damaging both circuit cab

as much as possible.3.14 In areas where there are m

separate cable trays shouldof duplex essential and non

3.15 Consideration should be gof BS 5588 and fire-protecroutes.

Primary sources of sup

3.16 This section deals with thedistribution and sub-distrielectrical infrastructure (PEpractice configurations forsupplies (seeFigure 1). Th

presented generally in ordeto high. The selection of a will be dependent on the sindividual design in terms supply, type of healthcare fpatient etc. Whichever conshould be based on a risk aappropriate level of resilien

3.17 The configurations presennot be taken as being definrestrictive. They are intendpractice and not intended any design.

Secondary main source generation

3.18 This section deals with secPEI and presents best pracboth HV and LV standby The configurations are preof resilience, from low to h


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Figure 1 Primary electrical infrastructure for healthcare premises

SOURCE OF ELECTRICAL SUPPLY

PRIMARY SOURCEPUBLIC ELECTRICAL SUPPLY

(PES) DISTRIBUTIONNETWORK OPERATOR

(DNO)LV (400 V) HV (11 kV)

OWV

OLTAGENETWORK(S)

HIGH

VOLTAGE

NET

WORK(S)

High Voltage

Substation

Low VoltageDistribution Switch Panel

Low VoltageSub Main (Unified)Distribution Board

Low VoltageSub Main (Segregated)

Distribution Board

Low VoltSub Main (Dua

Distribution

TERTIARY POSUPPLY

UNINTERRUPPOWER SU

ISPOW


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Figure 2 Secondary electrical infrastructures for healthcare premises


SECONDARY SOURHEALTHCARE PREMISES

INTERNAL ELECTRICAL INFRAST

AlternativeEnergyPlant

OWV

OLTAGE

NETWORK(S)

HIGH

VO

LTAGE

NETWORK(S)

High Voltage

Substation


Low VoltageSub Main (Unified)Distribution Board


Distribution Board

Low VoltageSub Main (Dual U

Distribution Bo

TERTIARY POW

SUPPLYUNINTERRUPTIPOWER SUPPL

ISOLPOWER

CombinedHeat and

Power (CHP)P


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responsible for the purchase of electrical energy,

they will also be responsible for the negotiations.However, in the more usual case where theelectrical energy is a pass-through cost, or wherethe building services operator is the healthcareorganisation, the healthcare organisation will beresponsible for the above negotiations.

3.20 The opportunities for alternative energy sourcesshould be explored wherever practical. For example,sources such as CHP or wind power will reduce thenet carbon emissions and potentially provide animproved economic solution. Where alternativeenergy sources are used, the resilience of such plantshould be considered. This may be in the form ofN+1 CHP plant or suitable alternative supplyfrom the DNO.

3.21 Healthcare organisations should use the NHSEnvironmental Assessment Tool (NEAT) bothto help find out how their facilities and servicesimpact on the environment and to estimate thelevel of environmental impact taking place (http://www.dh.gov.uk).

3.22 Where the proposed alterations are formodification and/or adaptations to the internalelectrical infrastructure, tariff negotiations may notbe required. Nevertheless, the use of alternativepower sources should still be considered to offsetthe increased electrical demand.

3.23 Guidance on the environmental benefits ofalternative energy sources can be obtained from:

Building Services Research and Information

Association (BSRIA) (http://www.bsria.co.uk);Chartered Institute of Building Services(CIBSE) (http://www.cibse.org);

Combined Heat and Power Association(CHPA) (http://www chpa co uk);

healthcare facility will h

one of the following vol11 kV Large

floor 11 kV/400 V Medi

typica8500

400 V TP & N Gene

healthclinicbuilddecon

230 V SP & N GP anoff-sit

The types of healthcare

are for illustration and voltage tolerances in thissue of the IEE Regulaand the Electricity SafeRegulations 2002.

3.25 Some larger sites may haintake point) with an in(seeChapters 68). In s

voltage will be either 11connection arrangemenresilience of supply.

3.26 Some healthcare sites, phave expanded over a numultiple intake points (same supply voltage). Tshould be consolidated at a common point. Sucprovide economies with

3.27 The DNO may arrange(under a wayleave agreeelectrical equipment, in

l l l l l d d b d
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cook-chill: the introduction of cook-chill has

meant more meals are cooked electrically andward-based regeneration ovens have beenintroduced;

electronic patient records (EPR) and patiententertainment systems: although these have avery low electrical power requirement, suchsystems require a significant increase incontainment and space.

3.29 Alterations to existing installations, unless plannedand allowed for during the original construction,can be costly, particularly when structural changesare involved.

3.30 Healthcare premises are frequently remodelledwithin the economic life of an electricalinstallation. Designers and stakeholders shouldidentify means of remodelling the electricaldistribution and determine to what extent anyflexibility for remodelling should be incorporatedwith the initial design.

3.31 Each electrical distribution centre should includean element of equipped and unequipped enclosuresfor retrofitting of switches, protective devices and

so on.3.32 The designers should evaluate, by risk assessment,

the degree of remodelling and natural expansionthat will be incorporated into the initialinstallation. The risk assessment should reflect bothclinical and commercial risks.

3.33 This allowance for growth and remodelling should

be incorporated into the adopted distributionstrategy (see Chapter 6).

Assessment of existing electricalsystems

Greenfield site

3.35 Where the proposed workand not part of an existingassessment of existing electlimited to an understandininfrastructure in the area. Thelp in determining the coreinforcements.

New-build on existing site

3.36 Where the proposed workwithin part of an existing cof existing electrical systemextent of any spare capacityconnection point. The conat the site intake or embed

distribution network. Thisdetermine the practicalitieany reinforcements of switdevices and cables.

New equipment on existing s

3.37 Where the proposed workinstallation of new equipm

of sub-distribution and finrequirements and an undedistribution (including findetermine the most appropand any reinforcements of devices and cables.

Load profile

3.38 Designers and stakeholderelectrical profile of the heastage. This will prove invalviability of any secondary asources (for example CHP


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premises such as GP surgeries. The figures do not

take account of any growth. Power densities at thelower end do not necessarily imply any improvedefficiency over power densities at the higher end.However, power densities outside the range maygive cause for further investigation.

Table 1 Typical range of power densities for ahealthcare facility over a five-year period

Power W/m2 GJ/100 m3

General power 925 3.710.3

IM&T power 36 1.22.5

Medical power 515 2.06.2

Lighting

General 915 3.76.2

Special 0.91.5 0.40.6

Task 1.352 0.50.8

Medical 01 00.4

3.40 Figure 3 shows a typical

hospital. The annual prThe actual shape and kVsite and a function of thprovided.

3.41 The various options of penergy required to satisfevaluated. Where the prshort peak maximum derelation to the average dDNO connection will bexpensive, as the cost ofoptimised at the maximcases, the healthcare orgdeveloping some of the site alternative energy sopower. Where alternativthe resilience of such pla

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time of day

kVA

Figure 3 Typical diurnal electrical profiles for a hospital

Figure 4 Typical annual electrical profiles for a hospital

Electrical services HTM 06 01 Electrical services supply and distribution: Part A Design considerat


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Diversity factors

3.42 The electrical diversity factor is the ratio ofinstantaneous power to the total installed power.Diversity factors can be applied to each element ofthe electrical service (for example the lighting loador low-power load) or to a whole department.

Where the healthcare site is large and has multiplesubstations, the diversity factors can be calculated

for each individual substation. It should be clearthat the diversity factor for a particular service (forexample lighting) may differ during the day andyear, while the diversity of, say, the chiller plantmay have a different cycle. Similarly, the diversityvariation for one department (for example

radiography) may be highe

than in the afternoon, whiemergency department maevenings.

3.43 The above variations in actthe true load profile as iden3.383.41above.

3.44 Designers should assess the

for each service and departjudgement of the site-wideThis figure can then be appower and the allowance fothe electrical capacity of thTable 2 shows some typica

Table 2 Typical electrical diversity factors for healthcare premises

Power density(W/m2)

PF Building diversity

Substationdiversity

Connectload diver

AHU fans 1525 0.95 0.70.90 1.00 0.70.9

Building services pump 13 0.95 0.70.90 1.00 0.70.9

Lifts 58 0.95 1.350.23 0.50 0.30.5

Chiller 2535 0.95 0.90.95 1.00 0.90.9General low power 925 0.95 0.490.60 0.70 0.70.8

Information systems 36 0.95 0.80 0.80 1

Medical equipment 616 0.95 0.350.49 0.70 0.50.7

General lighting 915 1.00 0.49 0.63 0.70 0.70.9

Specialist lighting 0.91.5 1.00 0.350.63 0.70 0.50.9

Task lighting 12 1.00 0.450.54 0.60 0.750

Medical lighting 01 1.00 0.420.54 0.60 0.70.9Notes:

Power density: The power density relates to the relevant internal floor area of the healthcare premises.

Power factor (PF): Power factor is assumed to be the corrected power factor at each substation.

Building diversity The building diversity reflects that not all substations within the healthcare premi


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Consideration for EMC requirements

3.45 Electrical installations must be compliant with therequirements of the Electromagnetic CompatibilityRegulations 2005. The regulations describe theelectrical installation as a manufactured item, andtherefore require the installation to be tested forelectromagnetic radiation and absorption.Procurement contracts for electrical equipment

associated with the distribution of the electricalinstallation should stipulate that the equipmentmust be compliant with the ElectromagneticCompatibility Regulations 2005.

Roles and responsibilities

3.46 The Electromagnetic Compatibility Directive(EMCD) and the Electromagnetic Compatibility

Regulations 2005 describe who is responsible formeeting compliance. There are only two partiesinvolved the manufacturer and the operator.In a healthcare building project:

the designer and installer of an integratedheating, ventilation and air-conditioning(HVAC) or power distribution control systemare the manufacturer;

the manager of the healthcare premises and thebuilding services maintenance organisation arethe operators.

It will not always be pos

equipment that is CE-mwith the EMCD. An inCE-marked and non-CESupply of non-CE-markproviding the installer wthe system can be sure tundue interference to thsensitive to the electrom

the equipment will be u3.47 The designer should ob

the installer demonstratpractice has been applieof any concessions grantcompliant with the instawhich may be used with

3.48 Designers and stakeholdequipment which is supmedical environment wto operate successfully inshould not emit excessivstatement assumes that has an approved policy fmedical equipment whi

designers or stakeholderinstallation.

Figure 5 Roles and responsibilities

Building owner/designer

Ensures system legallycomplies with EMClegislation

Requires documproof of complia



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Access for maintenance

3.49 In order to comply with the Construction, Designand Management Regulations (CDM) 1994,designers need to give due account for access andmaintenance at a very early stage of the design,irrespective of the size, complexity and extent of theproposed installation.

3.50 Electrical services should not compromise the

space and access routes for other services suchas mechanical and public health. Maintenancetasks should be carried out with the minimumdisruption to continuity of supply and business.

3.51 The following documents provide additionalinformation:

Health Technical Memorandum 06-01 Part B

Operational management;Health Technical Memorandum 00 Policiesand principles;

Defence Works Functional Standard DMG 08 Access and accommodation for engineeringservices: space requirements for plant access,operation and maintenance;

manufacturers operational and maintenancemanuals.

Commissioning procedures

3.52 Designers should consider how the installationwill be commissioned and how the required testmeasurements will be made. This will include the

inspection of services that may be hidden at thetime of handover. It will also include theimplications of any phased occupation (seeChapter 17for more information).

3.53 The design team should make an application toh k h DNO h l h

3.55 In cases where the new ins

embedded generator plantPV cells), the DNO will nmethods used to clear any energy sources in order thaonto the DNOs network.

3.56 For greenfield sites, it maycoordinate the activities ofoperator and energy supplcan be completed (see para

3.57 The DNO will reserve thenew installation where thecomply with its criteria.

Connection to the healthcare

3.58 Where the new installation

part of the healthcare sitesapplication to connect willcompletion certificate asBS 7671:2001. The healthentitled to conduct a rangethat the installation is safe any fault currents which mbefore reflecting onto the r

healthcare sites network.

3.59 The site engineer should reconnect a new installation does not comply with the Health Technical Memorasafety guidance. The site enthe right not to connect a

the installation compromistrategy of any other part o

3.60 At a very early stage of theprocurement planning), ththe power requirement andrequest for a suitable suppl

Electrical services HTM 06 01 Electrical services supply and distribution: Part A Design considerat


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4.1 This chapter deals with the assessment of risk andthe need to ensure that the design of the primaryelectrical infrastructure (PEI) adequately protectsthe end-user, and in particular patients, fromelectrical failures. It promotes multidisciplinarydesign-team and stakeholder involvementthroughout the design process to ensure anappropriate distribution strategy (seeChapter 6),

incorporating resilience, redundancy andduplication as necessary. This should identify anyresidual risks from the design. The identificationof the residual risks will enable the healthcareorganisation to manage their collective ownershipof risk management and hence make appropriatenon-electrical and/or fixed wiring operational andemergency contingency plans in accordance with

DH Emeregency Planning Guidance.

Introduction

4.2 A failure can occur at any point or at any timein any electrical system, regardless of the designstandards employed. The design and installation ofPEI systems inherently allows failure (by operation

of a protective device) to minimise the risk ofdanger and/or risk of injury. This is true of internalPEI systems as well as the wider PES networkdelivered by the DNO. The effects of accidentaldamage and the need for maintenance and trainingshould not be overlooked. It is essential that an

4.5 The design process shoupoints of failure are minappropriate level of resilRisk management carefuto a design strategy withrelationships, where cosbusiness continuity and

4.6 Failures of the PEI systeconsidered as a consequof the incoming DNO smain switchboard etc. Ithat the emergency powor tertiary power supplyfailure of the PEI itself ipoints of failure should during the design procesystem design may be dfailure.

Note

An inappropriate level of resfailure may compromise pati

Ownership and desig

4.7 The duties of the stakehdesign, or assessment aninfrastructure should enpracticable) that all risk

4 Understanding risk and ownership



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power source (SPS) to cover an outage of the

electrical system. The management of such residualrisks may therefore be to reorganise any postponedelective consultations.

Risk profile

4.8 This Health Technical Memorandum divides riskinto two core elements: clinical risk (subdividedinto patient and non-patient areas) and non-clinicalbusiness continuity risks (subdivided into medicalservices and engineering services). Designers andstakeholders should consult with medical andtechnical staff to evaluate the overall risk andthe measures proposed to address the perceivedoutcomes. Most critical within this assessment isthe mobility and degree of healthcare supportprovided to the patient, including medicalprocedures, critical care and continuity oftreatment.

4.10 Small healthcare premises such as GP practices andhealth clinics/centres may have areas that fall intoCategory 1 and possibly Category 2. Communityhospitals may have departments in Categories 1, 2and 3, but unlikely in Category 4 or 5. Large acute

healthcare premises and above may well havedepartments in all categories. There is no rule thatdefinitively places healthcare premises in any onecategory, or defines one category for a particularhealthcare site.

4.11 Each healthcare facility will have a mixture ofcategories (clinical risks and non-clinical businesscontinuity risks) in varying ratios. The assessedhigher clinical or non-clinical and businesscontinuity risk for any particular area willdetermine the adopted electrical infrastructurestrategy for that area. Designers and stakeholdersshould evaluate the economics of providingd ff d b ( Ch 6)

4.13 The consequence of a pow

categorised against some bgroups and patient care plascale from ambulant throuConsequence is also relatedterms of contingency arranpreparedness and business have a financial implicatiooperational consequence o

in terms of the operation ainfrastructure from the pophysical construction and managerial and technical soperate the electrical infras

4.14 The level of consequence obe evaluated as increasing wcategory, for instance, and per category will equally bduration and extent of the

4.15 IEE Guidance Note 7 (alsoaddresses special locationsIEE guide deals with speciand classifies the dependendepartments have on a sus

The guide relates in part toelectrical supplies and theirequirements. These classiftime performance (secondssupply following an interrucontrolled or otherwise.

4.16 Within a GP practice or hbe assessed as acceptable to

failure in a system, given thto be more mobile than paareas, and staff will be ableaffected area in the event oother end of the scale, for

th f

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point of treatment or care. For the purpose of this

guidance, the patient levels described are notintended to be exhaustive, but rather an aid toconsider the issues.

Category 1 Support service circulation

4.19 These areas do not directly relate to the patientenvironment of any group under Chapter 10in IEE Guidance Note 7. The areas includecirculation spaces, waiting areas, offices and non-patient care areas such as laboratories or financedepartments. Consequently, engineering servicesdo not have an immediate effect on the clinicaltreatment or safety of patients (notwithstandingthe requirements of the escape lighting and so onthat may be provided from a local tertiary power

source).

Category 2 Ambulant care anddiagnostics

4.20 These areas do not directly relate to the patientenvironment of any group under Chapter 10 in

IEE Guidance Note 7. The areas may includepatients in consultation (excluding examination)or general out-patient areas. Loss of supply maygive rise to disruption, inconvenience and areduced environmental quality but would notdirectly compromise patient clinical treatmentand safety. The loss of electrical power to otherengineering services (for example ventilation or

medical gases) equally will not cause concern forthe safety of the patient or staff. There may be a

Category 3 Emergediagnostics

4.21 These areas relate to thof group 0 under ChapNote 7. The areas willwards and some maternot generally connecteequipment. However, medical test equipmen

and connected externafor a short or intermittpatient monitors or ultClinical treatment andcompromised by an inpower. However, the inpower should be limitefor other engineering s

support of the clinical medical gases, hot andcommunication etc (nrequirements of the esbe provided from a loc

business continuity risconnected to the SPS fgreater than three hourequirements of the esbe provided from a loc



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Category 4 Patients in special medical

locations

4.22 These areas will relate to the patientenvironment of group 1 under Chapter 10 inIEE Guidance Note 7. The areas may includeLDRP (labour, delivery, recovery, post-partum)areas (maternity), endoscopy rooms, accident

and emergency general/minors, haemodialysisareas, ECG areas, nuclear medicine, radiographydiagnostic, magnetic resonance imaging (MRI),endoscopic examination rooms, urologytreatment areas, or therapy rooms andultrasound. Patients may have electro-medicalequipment, medical monitoring or medical testequipment connected externally to their bodyfor a prolonged period. Clinical treatment andpatient safety may be compromised (but notendangered) by any interruption of electricalsupply. Electrical protective devices shouldinclude an RCD, but may not require an IPScircuit. Supplementary equipotential bondingwill be required in the patient environment. Anyinterruption of the electrical supply to medicalequipment should be limited to within15 seconds. Consideration may be given toproviding an alternative electrical supply (tertiarypower supplies) within 0.5 seconds, subjectto the range of patient treatment. Otherengineering services used in support of clinicaltreatment should be connected to the SPSwithin 15 seconds of any interruption ofthe electrical supply (notwithstanding therequirements of the escape lighting and so onthat may be provided from a local tertiary powersource).

Category 5 Life support or complex

for a prolonged period. C

patient safety may be cominterruption of electrical natural electrical resistancreduced when electro-meparts are placed in the boequipotential bonding (wenvironment) should be psafety. Best practice provi

but not be limited to, IPSprovision of an alternativ(tertiary power supplies) of any interruption of therequired by the medical eengineering services usedof the patient clinical treaconnected to the seconda

within 15 seconds of anyelectrical supply (notwithrequirements of the escapbe provided from a local

4.24 Tertiary power supplies suparagraphs 16.316.19) oequipment, may be consi

limit the interruption of than 0.5 seconds. StandbChapter 8) may be considlimiting the interruption between 0.5 seconds and Category 4 or Category 5at risk from both a generalocal final subcircuit fault

enhanced levels of resilienpatient therapies may be provided by interleaved cor pendant. Such arrangeability to perform maintedisruption.

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where the loss of electrical power could affect

essential diagnosis of a patient or the ability tooperate a clinic. Essential items of building servicesand plant may also necessitate the closure ofdepartments in the event of a power failure wherethese services are not adequately protected by aresilient electrical system.

4.27 Consideration of the categories in Figure 7 shouldestablish a minimum acceptable risk option at the

point of treatment or care. For the purpose of thisguidance, the non-clinical and business continuitydescribed is not intended to be exhaustive, but anaid to consider the issues.

Category 1 Business support services

4.28 The business support areas are departments such

as finance, stores, laundries and workshop areas.In general, an interruption of the electrical supplymay not compromise the treatment or welfare ofpatients. It may be appropriate to provide a single-conversion UPS (see paragraphs 16.316.19) toallow certain systems such as computer applicationsto shut down safely. Electrical load managementsystems may prove useful where the interruption to

the electrical supply (for these areas) is for morethan four hours (seeparagraphs 8.178.19;notwithstanding non-patient safety measures withthe provision of a tertiary power source).

Category 2 Building services safety and security

4.29 The requirements for these facilities are covered byvarious British and European legislative documents,

for example BS 5839-1:2002. Typically, batterypacks or single-conversion UPS systems willsupport such requirements. An interruption of theelectrical supply could compromise the safety andwelfare of patients. These facilities may be included

on the SPS, where the s

loads would only represof the SPS. An understamaintenance and the capacks employed on thes(notwithstanding the relighting etc that may betertiary power source).

Category 3 Building servcontrol

4.30 The building services ensystems will include HVservices, energy centres management systems. Inthe electrical supply couto the treatment or welf

conversion UPS should certain systems such as cbe shut down safely. Elesystems should be consiinterruption to the electwater systems) gives an internal space temperatu(seeparagraphs 8.178.

requirements of the escaprovided from a local te

Category 4 Medical supp

4.31 The medical support areas disinfection units, laband physiotherapy. An isupply may represent a treatment or welfare of pconversion UPS (seepashould be provided to alcomputer applications t



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Electrical load management systems may prove

useful where the interruption to the electricalsupply (for these areas) is for long periods, saymore than two hours (seeparagraphs 8.178.20;notwithstanding the requirements of the escapelighting etc that may be provided from a localtertiary power source).

Electrical infrastructure

4.32 This Health Technical Memorandum divideselectrical infrastructure into two core sections:primary and secondary (see Chapter 6):

the two types of distribution may share thesame cables, which defines a unified electricalinfrastructure;

where there are two sets of cables common tothe primary and secondary distribution, thenetwork is said to be a dual-unified distribution;

where the primary and secondary distributionhas entirely separate cables, the distributionstrategy is said to be a segregated distribution.

The most resilient distribution strategy will haveboth dual-unified distribution and primary and

secondary power sources.4.33 Business continuity risk assessments evaluated by

cause-and-effect models may be used to analysethe impact of electrical failures on departmentswhich are reliant on the services provided. Withinthe integrated departmental model, considerationshould be given to the cause and effect of electrical

failures which escalate exponentially with time.

4.34 Cause-and-effect risk mod

the global electrical infrastpoint-of-use equipment. Tconsider single electrical famultiple electrical faults ansimultaneous multiple fauland 9).

4.35 A distribution strategy shodrives the risk of failure of

the point of use) to a low oA lower distribution strateredundancy of primary ansupply plant which still alevel indicated above shoconsideration may be givenhigher risk factor than the for a particular clinical area

Resilience

4.36 Overall, the PEI can be cosections:

supply;

distribution;

point of use.4.37 The essential elements of a

are:

redundancy;

moving the first singleto the point of use as p

Figure 8 Electrical failure risks evaluation to clinical categories

RISK OF ELECTRICAL FAILURE BY INFRASTRUCTURE

Distribution strategy (refer to Chapter 6)

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appropriate access for practical maintenance and

testing procedures.4.38 The resilience required to maintain essential supply

in the event of not only primary failures but alsosecondary failures should be considered. A suitableassessment of the likelihood of concurrent failuresoccurring within a foreseeable period should bemade, and therefore the operation and inter-relationship of the system and its component parts

should be fully understood. With regard to theconsequence and risk, any reasonably foreseeablesecondary failures should be appropriatelyprotected against. An example here may be astandby generator failing to start (second-line fault)on a supply blackout (first-line fault).

4.39 Incoming electrical supplies may be constrained by

what the DNO is able to provide, or what has beenassessed as cost-effective for the type of healthcarefacility. The distribution strategy should maintainthe minimum acceptable resilience level throughoutthe internal electrical system.

4.40 An iterative design process will help stakeholders toassess the distribution strategy. The process may beused to determine the location of the first single

point of failure in addition to the method used tomitigate the risks on the distribution downstreamof that point. The provision of tertiary supplies(UPS) on final distribution boards or the ability tomanually reconfigure the distribution may besuitable risk mitigation.

4.41 The effects of electrical power failures due tofaults at any level within the infrastructure can bedesigned out by the robustness of the network

resilience. The distribut

adequate resilience and testing and maintenancewithout placing patientsunnecessary risk. Such sredundancy in certain eexample generators, UPof resilience for maintenpractice.

Electrical infrastructu

4.42 A number of different eform the primary and sesystem (seeFigure 9). Sobe optional dependent oChapter 6) and requiredassessed risk from powerconfigurations of the eleelements will have risk-massociated with the possoccurring. Similarly, eacelements, and the links them will present additioverall risk of a power famitigated by the correctconfigurations and intersystem and component appropriate infrastructucategorised in terms of tresidual risks. Evaluatinmake selection of the apapparent at the point ofinfrastructure.



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Figure 9 Electrical infrastructure generic flow diagram


PRIMARY SOURCEPUBLIC ELECTRICAL SUPPLY

(PES) DISTRIBUTIONNETWORK OPERATOR (DNO)

LV (400 V) HV (11 kV)

LOWV

OLTA

GENETWORK(S)

HIGH

VOLTAGE

N

ETWORK(S)

High Voltage

Substation


Low VoltageSub Main (Unified) Distribution

Board


Distribution Board

Low VoltaSub Main (Dual

Distribution B

TERTIARY POSUPPLY

UNINTERRUPT

POWER SUP

ISOPOW

SECONDARY SOUHEALTHCARE PREMI

INTERNAL ELECTRICAL INFRA

AlternativeEnergy

Plant

CombinedHeat and

Power (CHP)


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5.1 The quality of the electrical supply is theresponsibility of the DNO, which will comply withthe requirements of the Electrical Safety, Qualityand Continuity Regulations. However, the use ofthe electrical energy within healthcare premises canaffect the quality of the internal distribution interms of power factor and harmonics.

5.2 Healthcare premises have numerous switch modepower supplies and inherently high inductiveelectrical loads and unless corrected, the powerfactor will be poor, requiring large transformers,cables and high-energy cost. Improving a typicalpoor power factor from say 0.75 lagging to anappropriate power factor of say 0.95 lagging willreduce the kVA demand by 20% and will bereflected as a utility cost savings. The actual

inductive load will vary throughout the day andyear. The inductive load will also vary across thesite according to the location of mechanical plant,lifts and to some extent the clinical departments.

5.3 The normal supply frequency is 50 Hz with atolerance of 1%. The nature of the electricalequipment used throughout the site can inject

secondary frequencies that cause significantdisturbances to the internal distribution and thesupply. The majority of secondary frequencies,known as harmonics, are generated from switch-mode power supplies found in a wide range ofelectrical and electronic equipment

electrical system will be correction equipment shdisconnected if the primand if used in conjunctigenerator plant (or CHPthe generator (or CHP precommendations. Whecorrection equipment is

appropriate cable sizes fshould be used.

Located at sub-main distri

5.6 Power factor correction main distribution boardoutgoing circuits will beof power factor correctio

main distribution boardloads can be corrected wwill save on the capital c

Where the power factorlocated at the intake andboards, the appropriate higher currents should bof the sub-main distribu

equipment may need ov

Located on the electrical e

5.7 Where individual pieceshigh inductive reactance

5 Power quality



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freestanding unit. Where a cubicle of the

switchboard is used to house the power factorcorrection equipment, consideration should begiven to the effect this will have on future flexibilityand remodelling of the power factor correctionequipment and/or the switchboard circuits.

5.10 Power factor correction equipment requires naturalventilation to remove the small amount of heat itgenerates. Further information on the amount of

natural ventilation should be available from themanufacturer.

Harmonics

5.11 The normal supply frequency is 50 Hz with atolerance of 1%. The nature of the electricalequipment used throughout the site can create

secondary frequencies that cause significantdisturbances to the internal distribution and thesupply. The majority of the secondary frequencies,known as harmonics, are generated from shortsurge currents and transient currents arising fromnon-linear electrical loads such as switch-modepower supplies and rotating machinery, variablespeed drives and so on found in a wide range of

electrical and electronic equipment.5.12 Surge transient currents are also caused by lightning

strikes. Further details on the lightning strikes andsurge arrestors can be found in paragraphs 13.3913.49.

5.13 Even-order harmonic frequencies are self-negatingand do not cause a real disturbance to the electrical

distribution. Odd-order harmonics with zerorotation effect, known as Triplen harmonicfrequencies (3rd-, 9th- and 15th-order), and odd-order harmonics (5th, 7th and 11th) can causesignificant disturbances leading to high currentsand voltages, and overheating of cables and

which then should be sized

heat. Consideration shouldof clean-earth conductors fitems such as IM&T comprooms. A single-phase thirbalanced three-phase circuat 70% of the fundamentathe neutral conductor. If threach the distribution tran

reflected into the primary circulate. The unchecked hprimary winding of a distrbe dissipated as unwanted

5.15 The network analysis of hapropagated within the elecmade and communicated tstandby generator. The gen

to reflect the anticipated hHarmonic currents not allgenerator design may caustorque loads and consequegenerator while running. Ofilters or isolating passive hused while the generator is5.18).

5.16 The electrical load of a typwith many modern medicaservices may have non-lineharmonic disturbances) at Unless the harmonics are cdownstream from the tranwinding, the transformer mby the factor-K method which may typically be 70nameplate kVA rating to adamage.

5.17 Alternative methods may it l d t i


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located here, as large harmonic currents may

require neutrals oversized by as much as 300%.5.19 Note for the purpose of this section of the

guidelines, the intake point means the HV/LVsubstation, LV switchboard. Alternatively, wherethe site has an internal HV network, the intakepoint means each such substation LV distributionboard.

Located at sub-main distribution boards

5.20 Harmonic filters may be installed at the sub-maindistribution board, in which case only the outgoingcircuits will be corrected. The advantage ofharmonic filters installed at sub-main distributionboards is that several sources of harmonic inductiveloads can be corrected with one common unit. Thiswill minimise the harmonic disturbance reflectedon the sub-main and main distribution cables andsave on the capital cost and space required.

Located on the electrical e

5.21 Where an individual piea high transient current mode power supply, it isharmonic filters direct tarrangement has the advharmonic disturbances ocables.

Voltage surge protec5.22 Consideration should b

of voltage surge protectiwhere equipment whichvoltage surges is connecinstallation from the int



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6.1 For the purpose of this Health TechnicalMemorandum, it is assumed that the highestdistributed voltage in any healthcare facility will be11 kV. DNO connections to healthcare facilitiesmay be at elevated voltages such as 33 kV, but it isconsidered that such voltages are not distributedwithin the healthcare site. Where healthcarefacilities do have a DNO connection at voltages

above 11 kV, the strategy for such connections(and if appropriate, distribution) should follow thedistribution philosophy described in this chapter.This Health Technical Memorandum onlyconsiders any electrical energy used at low voltageas a three-phase or single-phase connection. ThisHealth Technical Memorandum does recognise thatsome electrical energy used in healthcare premises

will be at SELV or PELV, but is only concernedwith the fixed wiring at low voltage. In a similarway, electrical energy used at high voltage, for somelarge vapour compression chillers for example, isacknowledged, but again this Health TechnicalMemorandum only addresses the fixed wiring atHV.

6.2 When designing the strategy for the electrical

network(s), it is essential to take a holisticapproach. The electrical system may includeHV and LV distribution networks, or just LVdistribution networks, depending on the size of thesite.

switchboards. While this cresilience provided by genedescribe the starting or concan be found inChapter 8

6.5 The resilience can be enhadistribution board with thsupplies such as UPS (seep

Alternatively, the resilience

battery packs fitted to medintravenous (IV) pumps. Falternative supplies can be This section deals with thethe fixed wiring network toresilience.

6.6 To achieve this resilience, a

designers should contributdebate (seeChapter 4).

6.7 The available electrical supverified with the DNO. Mbetween 500 kVA and 800(0.4 kV) connection. Supp750 kVA and 12 MVA shovoltage (11 kV). Where a h

assumed maximum deman12 MVA, the DNO conneor above. Clearly, where than AMD no more than 50electrical infrastructure wil

h AMD ll

6 Distribution strategy


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calculating the resilience of a system it is important

to consider elements that are mutually inclusiveand not mutually exclusive. For example, thestandby generator complement (with a commonpoint of coupling) would be a mutually inclusivesystem. The standby generator complement andprimary electrical infrastructure at a common pointof coupling are mutually exclusive. Best-practiceelectrical distribution strategy solutions provide

resilience to the first-fault conditions at a commonpoint of coupling. Distribution strategies thatprovide resilience above the first-fault condition(at a common point of coupling) are unlikely tobe economically viable. Distribution strategies thatprovide N+1 resilience at several different points ofcommon coupling are more robust andeconomically viable.

Supply connections

6.9 In electrical supplies to large healthcare premises(in electrical terms this means greater than2 MVA), a general arrangement with a dual-PESconnection should be adopted, arranged with eitheran auto-changeover or a manual-selection switch.Dual supplies with diverse routes may be

considered an economic strategy to maximise theresilience and minimise the actual single point offailure. They should originate, if possible, fromseparate DNO substations, ideally fed fromseparate parts of the National Grid, withindependent cable routes to the healthcare sitessubstations. However, the origin and nature of thePES supply routes will largely be beyond the

control of the designer or stakeholders.6.10 Two separate HV supply feeders (or LV if

appropriate) may provide an additional safeguard(for the healthcare site) against a PES connectionfailure. Whether this is practicable largely depends

99.999% (or 0.001% u

mean 5.25 minutes unaHowever, the issue is thfaulty transformer, whicDistribution strategies twith a common primarysecondary linked by a nwould provide a transfoN+1. While both transf

would share the instantaOpportunities for transfmaintenance are improvcontinuity of supply foloutage. Such arrangemeintake substation (ISS) iconnected in parallel orno load are not recomm

Risk of generator failures

6.12 Generators have many mlubrication, cooling andgenerator controls are elelectromechanical devicoutput in response to thgenerators should be ma

readiness state in order tfunction of standby supmay be of the order of 9unreliable), which equaunavailability per year. Tfailures are a result of thoccur during the first fiv

6.13 Distribution strategies tgenerators (each rated apoint of coupling with twould provide generatoThree standby generatorated at 50% of the con



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the guidance within this Health Technical

Memorandum (Parts A and B) and the guidancegiven in Health Technical Memorandum 06-02 Electrical safety systems:

cable faults within the private network;

inappropriate grading of protection devices;

poorly designed network with common pointsof failure;

reliance on one form of standby protection;

accidental isolation.

Distribution system high voltage

6.15 Healthcare premises with an AMD greater than800 kVA will require an internal HV network.There are two basic forms, radial networks (forAMDs up to say 3.5 MVA) and ring networks (forAMDs above 3.5 MVA).

6.16 The following simplified schematics are provided toshow the main HV supply arrangements. They arearranged generally in order of resilience from low tohigh, but their selection as a design solution will bedependent on the supply arrangement available

from the DNO, the type of healthcare facility, andthe level of assessed risk with regard to end-users.Where typical HV distribution arrangements areshown connected to the LV distribution, these areincluded only to assist in the understanding of theLV arrangements. LV distribution arrangements areconsidered more fully inparagraphs 6.316.59.This section does not describe the control of any

standby generator system (seeChapter 8 fordetails).

HV network one radial circuit with onesubstation only

6.17 A single HV supply from t

the healthcare sites HV-swsubstation. This would typ1500 kVA.

6.18 This type of distribution sta small to medium-sized aconly a primary source of sua single point of failure righdistribution switchboard(s

stakeholders should considby the additional resiliencedependent on the clinical r

6.19 The resilience of the HV sbe enhanced by including supply at the intake, as a seor an LV standby generatoClearly, generators at the Ladd resilience to the internmultiple LV standby generprovide any economic ben

HV network one radial circsubstations

6.20 InFigure 11, a single HV

feeds onto the healthcare spart of the substation. Froa single HV radial circuit cHV substations. Each of thtypically be up to say 1500AMD for the healthcare si800 kVA and 3.5 MVA.

6.21 This type of distribution st

appropriate for a healthcardetached buildings. The arsubstation do not exceed aof Category 2. As there is oof supply, this system creat


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generators could be local to each substation or in acommon central facility, depending on the spreadof the site. Clearly, the generator at LV switchpanelswould add resilience to the internal distribution.Having multiple LV generators at a commoncentral facility may provide economic benefit to thehealthcare facility during maintenance periods.

HV network three radial substation

6.23 In Figure 12, a single Hfeeds onto the healthcarpart of the substation. Fthree HV radial circuitsare connected. Each of t

typically be up to 1500 for the healthcare site w

Substation 3Substation 2Substation 1

The healthcare site

DNO connection

Figure 11 HV network one radial circuit, three substations

Substation ISS

DNO or site connection

Figure 12 HV network three radial circuits each with one substation



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and 3.5 MVA. This distribution network is

an enhancement of that inFigure 11above, asfailure of any part of the internal HV electricalinfrastructure will affect a smaller area. The dual100%-rated transformers (not operated in parallel)of substation 2 will provide improved transformerand switchgear maintenance opportunities for thatarea.

6.24 This type of distribution strategy may be

appropriate for a healthcare premises with manydetached buildings. The areas served by any onesubstation do not exceed a clinical risk assessmentof Category 3. As there is only a primary sourceof supply, this system creates a single point offailure right through to the LV distributionswitchboard(s).

6.25 The resilience of the HV supply ofFigure 12maybe enhanced by including a secondary source ofsupply at the intake as a second DNO connection.Standby LV generator(s) connected at the LVswitchpanels will enhance the infrastructureresilience and facilitate improved transformermaintenance opportunities. Standby generatorscould be local to each substation or in a commoncentral facility, depending on the spread of the site.Clearly, the standby generator at LV switchpanelswould add resilience to the internal distribution.Having multiple LV generators at a commoncentral facility may provide economic benefit to thehealthcare facility during maintenance periods.

HV ring network ring with four substations

6.26 InFigure 13, a single HV supply from the DNOfeeds onto the healthcare sites HV-switchboardpart of the substation. From the intake substationone HV ring-circuit connects to all other internalHV substations (which may be more than the fourshown here) Each of the substations would

intake substation should co

and all field substations shswitch type. SeeChapter 9HV protection and switch

6.28 This type of distribution stappropriate for a large acutother support facilities on served by the ISS substatioinclude clinical risk assessm

Category 5. The areas servsubstation 4 may include cof Category 3. As there is oof supply, this system creatfailure right through to theswitchboard(s).

6.29 The resilience of the HV sbe enhanced by including supply at the intake, as a se

Additional transformers at100% rated and not connestandby LV generator(s) coat the LV switchpanels, mainfrastructure resilience. Tsubstation may provide restransformer failure and/or generators could be local tcommon central facility, dof the site. Clearly, the genwould add resilience to theHaving multiple LV standcommon central facility mbenefit to the healthcare famaintenance periods.

6.30 The resilience of the HV renhanced if the ring normring control. Electrical fauto a discrete section of the

b t ti l b t t


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BS 7671:2001. Within special areas, medicalrisk Categories 4 and 5 and wet areas such aspost-mortem rooms, the wiring system would

6.33 The method of fire protfor essential distributionopportunities for flexibl

Figure 13 HV ring network ring with four substations

Substation ISS

SubstatSubstation 3Substation 2

The healthcare site

PES

DNO connection



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Primary supply unified infrastructure

Figure 14 Primary supply unified distributionsystem

6.35 This is the simplest form of LV infrastructure witha primary supply only, direct either from the DNOor from a single HV transformer arrangement,feeding a unified LV distribution network. The

transformer switchgear and main cables should berated to take the AMD and an allowance forgrowth (seeparagraphs 3.283.33).

6.36 The first single point of failure will be theconnection point (to the DNO healthcare sitestransformer). A LV infrastructure of this kind isappropriate for clinical risk Categories 1 or 2 (seeparagraphs 4.124.24). This infrastructure does

not provide for inconvenience-free maintenanceopportunities. Therefore, the infrastructure lendsitself to healthcare premises that do not operate24 hours a day/7 days a week (24/7) facilities, andhence give rise to operational windows in business

6.39 This simple arrangement m

for GP practices, health ceaccommodation, dependenof risk posed by a failure.

Primary and secondary supplsegregated infrastructure

6.40 This form of LV infrastrucsupply, connected directly

or the healthcare sites trandistributed secondary suppinternal LV switchboard. Tswitchgear and main cabletake the AMD and an alloparagraphs 3.283.33). Hogenerator is rated only for part of the healthcare sites

6.41 The first single point of faiconnection point (to the Dtransformer) for the unifieHowever, the segregated essingle point of failure mucuse. This infrastructure doinconvenience-free mainteall areas. Therefore, the inf

healthcare premises that haand part non-24/7 facilitieinfrastructure resilience anstandby generator units toimprove the maintenance obusiness continuity. Alternmanagement system couplinterconnect the essential a

(via cables or a manual bussimilar increased resilience

6.42 An assessment of the potenremodelling the healthcaremade to understand how t

Substation ISS

Risk

category 1

Risk

category 1

Risk

category 2


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6.44 The first single point of failure will be at the main

LV switchboard for the unified circuits, and at thepoint of use for the dual-unified circuits. A LVinfrastructure of this kind is appropriate for clinicalrisk categories 2, 3 or 4, where the dual-unifiedcircuits are used in Category 3 or 4 risk areas (seeparagraphs 4.124.24). This infrastructure may

provide for inconvenien

opportunities in the CaHowever, the same oppthe Category 1 and Catthe infrastructure resiliestandby generator subjeThere is no resilience wi

Substation ISS

Risk category 3 or 4

Riskcategory 2

Riskcategory 1

G

Figure 15 Primary and secondary supply unified and segregated infrastructure

G

From healthcare sites networkor DNO connection

Figure 16 Primary and secondary supply unified and dual-unified infrastructur



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and/or switchgear for the Category 1 and Category

2 risk areas. The unified circuit infrastructure lendsitself to that part of the healthcare premises that donot operate 24/7, and the dual-unified circuitinfrastructure (Category 4) lends itself to thosewhich do operate 24/7.

6.45 Enhancing the infrastructure resilience maybe achieved by adding a tertiary power source.A single-conversion UPS may be connected to

dedicated final circuits of the unified distribution.Enhancing the dual-unified infrastructure resilienceand adding additional standby generator units mayimprove the maintenance opportunities andbusiness continuity for the Category 3 or 4 riskareas.

6.46 An assessment of the potential for expansion and/orremodelling the healthcare premises should bemade, to understand how the LV distribution couldaccommodate such adaptations. This arrangementmay be appropriate for a general acute or largeacute hospital with additional support services,dependent on the assessed level of risk posed by afailure.

Dual primary and dual secondary supply unified

and dual-unified infrastructure

6.47 The LV infrastructure shown in Figure 17 has adual-primary supply, connected directly to eitherthe DNO or the healthcare sites transformer, anda dual-distributed secondary power supply alsoconnected at the intake LV switchboard. Thetransformer, standby generator, switchgear and

main cables should all be rated to take the AMDand an allowance for growth.

6.48 The first single point of failure will be at the mainLV switchboard for the unified circuits, or at thepoint of use for the dual-unified circuits. A LV

single-conversion UPS (see

may be connected to dedicunified distribution. Enhainfrastructure resilience anstandby generator units mamaintenance opportunitiefor the Category 3 or 4 risk

6.50 An assessment should be mfor expansion and/or remo

premises and how the LV dand17could accommodatarrangement may be approor large acute hospitals witservices, dependent on theposed by failures.

6.51 Figure 17 shows a potentiaa CHP plant. The schematmany potential electrical cplant. Designers and stakeideal CHP connection basblack start t

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