Chapter 6:Creating Robust Electrical System

What you will learn:• Key element for building a reliable DC electrical system

• Design strategies for in-room and standby electrical infrastructure

• Best practice for labeling and system monitoring

• End-to-end testing procedures

Recommended Electrical system Features

• The system should be dependable and ensure the continuous running for DC components (servers, networking devices,…etc)

• Electrical system should be studied and planed carefully

• System features that need to be included in the design:

System features to avert unnecessary downtime.

• Isolated Power• Avoiding Single Points of Failure• Maintenance Bypass Options• Remote Infrastructure Management

Recommended Electrical system Features (Cont.)

• Isolated Power– D ifferent power source for DC equipments than other electrical

devices in the building

• Avoiding single point of failure1. provide standby power system2. redundancy for critical devices and functions3. physical separation for key systems4. don’t share circuit breakers5. plan for additional electrical power in the future

Recommended Electrical system Features (Cont.)

• Maintenance Bypass Options• Design the system so that regular maintenance can be

performed without the taking major components offline

• Remote Infrastructure Management• Consider computer based building management

system for mid and large size DCbenefits of such systems would include 1. Early warning of problems 2. Savings in terms of staff and running costs

Chosen system should provide high interoperability, easy to program, graphic interface and produce useful data metrics

In-Room Power

• Electrical infrastructure elements include:1. Power distribution units 2. Circuit breaker panels3. Electrical conduits4. Wiring configurations

• Choose how to terminate, route and label the components

• Pre power cabinet locations with power receptacles

In-Room Power (Cont.)Determining Power Requirements:• Electrical infrastructure should support the room with its full capacity (completely full

with servers)

• The more information about incoming DC equipments the more accurate calculations for electrical needs

• Provide abundant number of circuits

• Basic formula for the maximum power needed:max kva =(volts * amps)/1000

example: for a DC with 50 cabinet locations each with two power strip (120 volts & 20 amps)

In-Room Power (Cont.)Power Distribution:

• Run flexible electrical conduits(whips) from large power distribution units(PDU) directly to each cabinets for small DC

• Use segmented power for large server environment (running electrical conduits from PDUs to circuit panels at the end of each row and then a subset of connections to server cabinet locations). This option would be easier to manage, less expensive more resistant to physical accidents

Power Redundancy:• Require for redundant power supply for each server and network equipment

and plug each one into different receptacle

In-Room Power (Cont.)

Figure 6-3. Direct-Connect Power Figure 6-4. Distributed (segmented)Power

In-Room Power (Cont.)• Wiring, components &termination options:• Be familiar with local power requirements (220/240 volts vs.

100/127 volts) and predominant power requirements for incoming equipments

• Good design practice:1. Use flexible whips (easier to install, less expensive, rearranged

quickly)2. Use heavy gauge of wire (the lower the gauge the thicker the

wire)3. Don’t terminate more than one receptacle on a conduit4. Avoid dirty power

In-Room Power (Cont.)Labeling & Documentation:

• Use thorough and unambiguous signage, labeling and documentations that is understandable by everyone

• Label power receptacles with the circuits they possess and the location in the circuit breaker panel where they originate.

• At that breaker panel, list all of the circuits it contains and which cabinet locations they are located at

• Use color-code to indicate parallel infrastructure

• Create a blue print of the room during construction (as-built) and keep it updated

• Mark electrical equipments that users need to stay away from it with hazard tapes

In-Room Power (Cont.)Convenience Outlets:

• Install convenience electrical outlets in multiple locations to be used instead of cabinet power outlets for rechargeable batteries, power drill, vacuum cleaner, …etc.

• Don’t connect these outlets to the standby power system

Emergency Power Off (EPO)• Required by fire codes in many countries • Intended to prevent fire suppression materials from coming into contact with

live electrical current• EPO types:

1. Push-up button (easy to use, most common EPO controls)2. Pop-up button (second frequently used, require a new piece of glass to restore

power, accidental activation is less likely)3. Control Knob (require the knob to be rotated 90 degrees to activate, better design,

simple to use, accidental activation is less likely)• It is highly recommended to cover EPO controls with a transparent plastic shell,

wired to an audio alarm.

In-Room Power (Cont.)

Figure 6-6. Sample Emergency Power Off Controls

Standby Power• Aimed to keep servers & network devices running when main powers fails• 3 factors for designing standby system

1. Redundancy (the more level of redundancy the more complex and expensive the system would be)

2. Simplicity3. Cost

• Load requirements (start with max. kva load the room can produce and then adjust in 2 ways:

1. Size the standby infrastructure to handle 110 to 120 percent of the projected maximum power needs

2. Build out your standby infrastructure based upon what level of redundancy you want for your server environment

• Design the standby system to handle both network & server rooms if they are close to each other, otherwise, have separate standby infrastructure if the network room is far from the servers room

Standby Power (Cont.)Batteries:• UPS is considered the most common source of standby power

• Use one UPS for each cabinet for small server environment or temporary DC as they are portable and inexpensive

• large floor-standing UPS model installed in the electrical room are used for all other size of DC as they are more robust, have greater capacity

• Run time term is used to identify how long standby infrastructure can support DC electrical load

• Required run time should be built on the assumption that the room is fully loaded

Standby Power (Cont.)Generators:• Size the generator to support at least 10 percent more than DC maximum

power capacity

• Skip installing generators in small server environment with reliable utility power and invest more in installing UPS that has 2 hrs of run time

• It is recommended to have generators that can run for 8 hrs before refueling

• Use enclosed protected area to install generators with short distance from DC

1. Protect against unauthorized employees 2. Protect against noise and vibration

• A good ventilation and enough space around the unite is required

Standby Power (Cont.)Monitoring Lights:

• Install monitoring lights high up on the both side of the wall inside (DC entrance, end of DC major aisles), outside and other strategic locations in the DC to indicate standby system activation

• Use different color demes for UPS and generators (avoid amber or white as they are used for fire alarms)

• Using large rotating beacon-style lights are recommended

• Installing monitoring lights outside the DC with an explanation signage with emergency phone number would help non DC users to report such incident

Standby Power (Cont.)

Figure 6-7 Monitoring Lights for the Standby Power System

Labeling and Documenting

• Make the labeling consistent with the servers room as possible (using the same terms and labeling schemes)

• Maintain a wiring diagram and keep it current

• No common standards for orienting electrical switches, on common and simple practice is to mark on position for all circuits and switches

Installation and Grounding• Installing of grounding system help protecting electrical

infrastructure and people from excess electrical charges (generated by faulty circuits, static dischargers, or lightening strike)

• Grounding system usually involves copper wires connected to the building steel and linked to copper rod deep in the ground (moist soil)

• Install a second grounding system “Single Reference Grid” to provide more protection to servers and network devices from interference, it should be connected to each power distribution unite and air handler

Testing and Verification• The contractor must perform a series of tests before any

servers/devices are installed in the DC to make sure that the infrastructure work as it should be

• Area of testing1. Load bank test (make sure that both UPS and generator can support the level of

power as designed, the goal is to check the max. capacity and runtime of the UPS)2. Injection test (injecting electrical current through circuit breakers to ensure that they

perform correctly during a real life power spike) 3. Circuit & labeling verification (at least for the main breakers and recommended for

all circuits)4. Full power test (cutting DC utility power to verify transferring of electrical load to

standby infrastructure and back again)5. EPO system test (activating EPO controls to ensure that all power sources and outlets

shutdown properly)

Testing and Verification (Cont.)

Table 6-1. Typical Load Bank Test

Testing and Verification (Cont.)

Table 6-2. Typical Full Power Test and EPO Check

Common Problems• Power receptacles or circuit breakers are mislabeled (obtain a

power tester and have two people verify all receptacles in the room)

• Monitoring lights for standby power are wired incorrectly (having monitoring lights configured to engage after 30-second which may result in no one will see UPS monitoring lights activation)

• Circuit breakers are left off (this may confuse people, they may think serious problem exists)