Electrical Supply Earth Continuity Series A

7/29/2019 Electrical Supply Earth Continuity Series A

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Electrical Supply & Earth

Continuity

REVISION PRESENTATION

Series A


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Mandatory Requirements!

Electricity at work Regulations1989 covers the follow areas:

The selection

Use

Positioning

Installation & Connection


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Consumer Units

These are installed directly afterthe electricity suppliers meter.

They hold a variety of different sizefuses or circuit breakers.

Providing protection for all electrical

circuits within the dwelling.


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Illustration of an electrical supplyentering a dwelling & connecting to a

consumer unit


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Main Supply Cable

The incoming main supply cable meter& main fuse are the responsibility of

the electricity supplier.

If damaged the electricity supplier

should be contacted to repair the cable/ fuse / meter.


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Individual Circuits

Ring Mains = 30 amp

lighting = 5 amp

cooker = 30 amp

water heater = 15 amp

Electric showers, Immersion Heaters, & Cookershave there own independent circuit separatelywired back to the consumer unit from theappliance.

If circuit breakers are used sometimes they canbe rated slightly higher then the fuse wire used onfuses e.g a heating circuit would use a 6 ampcircuit breaker & a power circuit feeding socket

outlets would use a 32 amp circuit breaker.


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Illustration of an Immersion Heaterradial circuit


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Voltages

Domestic dwelling voltage = 240 volts.

Industrial process require a highervoltage to operate large plant = 415volts this is often referred to as a three

phase supply.


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Equipotential bonding

An earth system that bonds all the main services suchas oil, gas, water.

They should be bonded at the point they enter the

building & wired back to the main earth block at theconsumer unit.

The cable should be a minimum cross sectional area of10mm squared.

It is a requirement of the wiring regulations that allexposed metal work within a building is bondedtogether.


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An illustration of Equipotential bonding.


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Earth connections

When connecting Equipotential bonding or supplementarybonding wires an earth clip is generally used, BS 951.

These clips should have a label attached readingsafety

electrical connection do not remove. Supplementary bonding picks up on the one metal areas the

Equipotential bonding has touched & cross bonds all otherexposed metal pipes & fixtures in the dwelling.

This is done in 6mm cross sectional area yellow & green earth

cable. Where a metal pipe is broken by a plastic fitting it is

important to cross bond the plastic to maintain earthcontinuity.


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Earth connections cont..

Earth wire can be identified by its colour green &yellow strips, on flex but on house wiring, twin &earth cables the bare earth wire should be sleeved

/ covered when the final connections are madewith green & yellow insulation material.

The top pin on a three pin plug is the largest thisis the pin the earth is connected to.

Generally when wiring a plug the earth is fixed insuch a way that should the flex be pulled hard theearth would be the last conductor to bebroken.


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Temporary Continuity EarthBonding

Removed these should be used by theinstaller when disconnecting a section ofpipe-work to protect yourself & the customeragainst electric shock.

These bonding leads resemble a car jumplead with crocodile clips on each end &

approx. 1.5 metres long They must have a minimal cross sectional

area of 10mm squared.


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Colour coding for domesticelectrical wires

Flexible cables: live = Brown, Neutral = Blue,Earth = Yellow & Green.

General semi rigid cables house hold wiring currentlystands with:

Live = Red

Neutral = Black

Earth = bare copper wire which is normallysleeved by the electrician.

However regulations have just been amended soshortly we will see semi rigid cables with thesame wiring colours as flexible cables.


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Double Pole switches

These are used generally on boilers,immersion heaters.

They break not only the liveconductor like a normal switch but

the neutral conductor as well,preventing the risk of electric shockthrough reverse polarity.


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RCBs Residual CurrentCircuit Breaker

These are generally supplied with expensiveshower pumps or whirlpool baths & baths

with electric seats to lift individuals in & outof the bath.

They protect the motors & pumps fromburning out by sensing any difference in

current flow between the live & neutralconductors.

Should a difference be detected the breaker

trips & protects the appliance.


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Socket Outlets

Double or single some have switchs somedont.

They are rated to supply a maximum of13 amps.

New double & single 13 amp socket outletsare only cable ofaccepting flat pin 13

amp plugs. Plug in testers known as Martindale testers

are used to check for the correct wiringof socket outlets.


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Switches in Bath / Showerrooms

No 13 amp sockets or rocker typeswitchs are allowed in either of these

rooms.Any light switch or electric shower

isolator or room heaters must be via a

ceiling mounted pull cord.


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Installation Practices

Electrical 13 amp socket outlets & light switches canbe surface mounted or let into the wall either waythey need back boxes.

Metal back boxes that are let into the wall need tohave rubber grommets fitted to the knock outholes to protect the cable as it passes through themetal box.

Where cables are buried in walls they need to beprotected by metal or plastic conduit or channel.

Where cables pass through holes in drilled joists theyshould be a minimum of 50mm down from the

top to prevent them being nailed.


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Protecting Cables


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Cable Care

Care needs to be taken with electriccables avoid:

Kinks, Knots or coils

Running cables under loft insulation

The cables in all these situations couldbecome overheated causing MCBs totrip, fuses to blow or possibly even a fireoutbreak if the fuse or MCB is not

activated.


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Connecting Appliances toExisting Supplies.

Normally this is straight forward simply checkthe fuse rating of the appliance & connect the

appliance via a plug to the nearest socketoutlet on the ring main.

However if a socket outlet is not near wherethe appliance needs to be a spur needs to be

cut into the ring main via ajunction box orby connecting into the back of an existingsocket outlet.


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Illustration of a spur being taken froma ring main circuit.


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Electrical Guidance

Electrical guidance can be found inBritish Standards.

BS 7671 generally covers all aspects ofthe statutory regulations in force.

The procedures for tests carried

out on electrical installations canalso be found in BS 7671


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Testing Electrical Circuits

All new electrical circuits should be tested beforeconnecting to a mains supply.

This is generally carried by doing a polarity test

using a multi-meter on a low ohm setting. By carrying out this test we can establish

whether all the conductors to a socket outlethave be connected to correct terminals

By placing the multi-meter probes on the live,neutral & earth connections of the fuse spur outlet &the appliance, checking one at a time, then checkingthe reading of the meter is less then 1ohm we no we

are safe to turn on the appliance, once we havechecked for earth continuity.


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Testing Electrical CircuitsCont..

Earth Continuity this is a test to ensure that anymetal workwithin an installation is not a safetyhazard.

A multi-meter is used on a low setting say 200 ohmsone probe should be positioned on a known earth& the other probe on the exposed metal work i.ebath, sink, boiler casing, again the reading should

be less than 1 ohm. The Earth connections should be checked visually

to ensure that the whole wire is located underneaththe terminal fixing screw.


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Test Equipment carrying out an EarthContinuity Test


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Safe isolation Procedures

Check the supply is live.

Turn off the supply at the consumer unit.

Retain the fuse or lock the MCB. Place a warning notice on the consumer unit.

Check the supply is dead.

Recheck your test equipment is working. Carry out the service /replacement.


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Essential Equipment


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Permanently Decommissioningan Electrical Supply

When we are permanently decommissioningappliances such as electric showers we should alwaysisolate at the consumer unit to avoid getting a

potential shock, which could occur when unwiring thecable from the ceiling pull cord isolator.

When decommissioning electrical appliances that

effect hot water being used in a dwelling it isimportant to liaise with other users of electricitybefore shutting off the supply.

Electrical Supply Earth Continuity Series A

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