Domestic Electrical Testing to BS7671 (17th Editition)

There is little point in setting up Regulations to control the way in which  domestic electrical installations are designed and installed if it is not verified that they have been followed. For example, the protection of installation users against the danger of fatal electric shock due to indirect contact is usually the low impedance of the earth-fault loop; unless this impedance is correctly measured. this safety cannot be confirmed. in this case the test cannot be carried out during installation, because part of the loop is made up of the supply system which is not connected until work is complete. Domestic electrical testing is important.

In the event of an open circuit in a protective conductor, the whole of the earthed system could become live during the earth-fault loop test. The correct sequence of testing would prevent such a danger, but the tester must always be aware of the hazards applying to himself and to others due to his activities. Testing routines must take account of the dangers and be arranged to prevent them. Prominent notices should be displayed to indicate that no attempt should be made to use the installation whilst testing is in progress.

The precautions to be taken by the tester should include the following:

1. - make sure that all safety precautions are observed

2. - have a clear understanding of the installation, how it is designed and how it has been installed

3. - make sure that the instruments to be used for the tests are to the necessary standards (BS 4743 and BS 5458) and have been recently recalibrated to ensure their accuracy

4. - check that the test leads to be used are in good order, with no cracked or broken insulation or connectors, and are fused where necessary to comply with the Health and Safety Executive Guidance Note GS38

5. - be aware of the dangers associated with the use of high voltages for insulation testing. For example, cables or capacitors connected in a circuit which has been insulation tested may have become charged to a high potential and may hold it for a significant time.

8.2.1 - Notices and other identification

The installation tester, as well as the user, must have no difficulty in identifying circuits, fuses, circuit breakers, etc. Re must make sure that the installation is properly equipped with labels and notices, which should include:

I. - Labels for all fuses and circuit breakers to indicate their ratings and the circuits protected

2. - Indication of the purpose of main switches and isolators

3. - A diagram or chart at the mains position showing the number of points and the size and type of cables for each circuit, the method of providing protection from direct contact and details of any circuit in which there is equipment such as passive infra-red detectors or electronic fluorescent starters vulnerable to the high voltage used for insulation testing.

4. - Warning of the presence of voltages exceeding 250 V on an equipment or enclosure where such a voltage would not normally be expected.

5. - Warning that voltage exceeding 250 V is present between separate pieces of equipment which are within arm's reach

6. - A notice situated at the main intake position to draw attention to the need for periodic testing

7. - A warning of the danger of disconnecting earth wires at the point of connection of:

a). - the earthing conductor to the earth electrode

b). - the main earth terminal, where separate from main switchgear

c). - bonding conductors to extraneous conductive parts The notice should read Safety electrical connection - do not remove

8. - A notice to indicate the need for periodic testing of an RCD.

9. - A notice for caravans so as to draw attention to the connection and disconnection procedure as indicated in

10. - Warning of the need for operation of two isolation devices to make a piece of equipment safe to work on where this applies

11. - A schedule at each distribution board listing the items to be disconnected (such as semiconductors) so that they will not be damaged by testing.

12. - A drawing which shows clearly the exact position of all runs of buried cables.

Table 8.5 - Correct sequence for safe domestic electrical testing
BEFORE CONNECTION OF THE SUPPLY
1	Continuity of protective conductors
2	Main and supplementary bonding continuity
3	Continuity of ring final circuit conductors
4	Insulation resistance
5	Site applied insulation
6	Protection by separation
7	Protection by barriers and enclosures
8	Insulation of non-conducting floors and walls
9	Polarity
10	Earth electrode resistance if an earth electrode resistance tester is used
WITH THE SUPPLY CONNECTED
11	Earth electrode resistance if an earth-fault loop tester or the ammeter and voltmeter method are used
12	Confirm correct polarity
13	Earth-fault loop impedance
14	Correct operation of residual current devices
15	Correct operation of switches and isolators

Domestic electrical testing saves lives and property, don't delay get tested to-day.

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