Replacing Domestic Electrical Accessories

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The replacement of domestic electrical accessories such as light switches, plug sockets, light fittings and other items of electrical equipment are considered by the BS 7671 to be minor works providing they do not alter the circuit arrangements. When these items are replaced you will be given a ‘Minor Electrical Installation Works Certificate’. This electrical certificate is your proof that the electrician did conduct the necessary electrical safety tests on the circuit he was working on.

You should be aware however that if the electrician finds an unsafe situation, he will suggest that you order additional works to bring the installation up to standard before the work initially requested can be undertaken. Also note that circuits in the property that are not included in the work will not be tested and will not be covered by the certificate being issued.

The tests conducted as part of a minor electrical works are discussed below.

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Damaged surface mounted socket Removing loose plastic after isolation

Damaged surface mounted socket

Removing loose plastic after isolation

Exposing the cables Ready to replace pattress box

Exposing the cables

Ready to replace pattress box

Inspection of electrical installations

Before any works to replace an accessory can begin the electrician will inspect the electrical installation to check its general condition, to note any departures from BS 7671 and to identify the equipment at the origin of the installation and the earthing arrangements. With regard to earthing, the electrician will be looking to identify whether the installation has a TN-C, TN-C-S or a TT arrangement. As earth loop impedances differ and TT installations require protection by a 100mA RCD in addition to the 30mA RCDs protecting the circuits.

The inspection will also identify the size of the earthing cable and the protective bonding. The size of these cables varies depending on the incoming supply, but with a 100A distributors fuse the sizing will be as follows 25mm meter tails, 16mm earthing conductor, 10mm protective bonding conductors.

Cables through pattress box Replacement double socket fixed

Cables through pattress box

Replacement double socket fixed

Socket in place ready for testing Initial confirmation of connections

Socket in place ready for testing

Initial confirmation of connections

Electrical safety tests as part of a minor works

The circuit resistance will be checked with either an R1 + R2 test or an R2 test. This can be used to calculate the Zs, the earth fault loop impedance. This test is important as it confirms the continuity of the circuit protective conductor back to consumer unit.

The condition of the cable will be tested using an insulation resistance test where 500 volts DC will be applied to the cables that carry a 230 volt supply and the resistance recorded in MΩ. Other tests include the Zs taken by measurement, checking polarity to ensue that switches and cut-outs are situated in the line conductors. RCDs will be checked to insure that tripping times are within prescribed maximum limits

 

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