Domestic electrical testing

Written by Admin. Posted in Electrical testing

Domestic Electrical Testing to BS7671 (17th Edition & the new amendments Jan 2012)


Domestic fixed wiring testing
Landlord electrical testing
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Domestic electrical testing

domestic electrical testing,fixed-wire

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. Domestic electrical testing ensures this impedance is correctly measured and then safety can 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.

Although the UK has a fairly good record of electrical safety, there are still over 30 deaths and nearly 4000 injuries from electrical accidents and the 8000 fires that occur in the home each year. Most of the accidents in the home involve faults in, or misuse of, domestic appliances, flexes, plugs or connectors. A large number are related to electrical maintenance or DIY activities. The major dangers to health from electrical accidents are from shock, burns, electrical explosion or arcing, fire, and mechanical movements initiated by electricity.

Domestic electrical testing saves life and property.

Please remember if you do not have the results of previous test and/or wiring diagrams then a great deal of time is required to determine the detail of each circuit!

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.Domestic electrical testing for safety.

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

domestic electrical testing for safety1. - 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.

Domestic electrical testing of sockets


8.3.1 - Why is correct sequence important?

Domestic Electrical Testing can be hazardous, both to the tester and to others who are within the area of the installation during the test. The danger is compounded if tests are not carried out in the correct sequence.

For example, it is of great importance that the continuity, and hence the effectiveness, of protective conductors is confirmed before the insulation resistance test is carried out. The high voltage used for insulation testing could appear on all extraneous metalwork associated with the installation in the event of an open-circuit protective conductor if insulation resistance is very low.

Again, an earth-fault loop impedance test cannot be conducted before an installation is connected to the supply, and the danger associated with such a connection before verifying polarity, protective system effectiveness and insulation resistance will be obvious.

Any test which fails to produce an acceptable result must be repeated after remedial action has been taken. Any other tests, whose results may have been influenced by the fault concerned must also be repeated.

8.3.2 - Correct testing sequence

Some tests will be carried out before the supply is connected, whilst others cannot be performed until the installation is energised. {Table 8.5} shows the correct sequence of testing to reduce the possibility of accidents to the minimum.

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 is used

WITH THE SUPPLY CONNECTED

  1. Earth electrode resistance if an earth-fault loop tester or the ammeter and voltmeter method are used
  2. Confirm correct polarity
  3. Earth-fault loop impedance
  4. Correct operation of residual current devices
  5. Correct operation of switches and isolators

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

Domestic electrical testing and inspection

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