Domestic Electrical Testing

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There is little point in setting up Regulations to control the way in which 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. 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.

       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.



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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.

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Continuity of protective conductors



Main and supplementary bonding continuity



Continuity of ring final circuit conductors

1

Insulation resistance

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Site applied insulation



Protection by separation



Protection by barriers and enclosures



Insulation of non-conducting floors and walls

2

Polarity

3

Earth electrode resistance if an earth electrode resistance tester is used +,, -../0') ' c



Earth electrode resistance if an earth-fault loop tester or the ammeter and voltmeter method are used



Confirm correct polarity



Earth-fault loop impedance

1

Correct operation of residual current devices

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Correct operation of switches and isolators

The IEE recommends the maximum period between periodic inspection and testing is: y?

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 - 10 years or change of occupancy

y?

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 - 5 years or change of occupancy

y?

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  - 5 years

y?

    
 - 3 ʹ 5 years

y?

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y?

   eg. Swimming Pools - 1 year

    a visual inspection but a full inspection and testing of the system y?

Identifies if any electrical circuits or equipment are overloaded

y?

cetects any potential electrical shock risks

y?

ciscovers any fire hazards in your electrical installation

y?

rinds any defective cIY electrical work

y?

Oeveals any lack of protective earth /bonding

y?

cetails the type of fixed wiring system and its condition

y?

shecks the suitability of the consumer unit

y?

Examines the equipment e.g. switches, socket-outlets and light fittings

y?

Tests any residual current devices

y?

ciscovers any wear and tear, damage or other deterioration

The test and inspections would include: y?

Öisual inspection

y?

sharacteristics of supply at the origin of the installation

y?

Protective conductors continuity test

y?

Oing sircuit sontinuity

y?

Insulation resistance test

y?

Polarity

y?

Earth electrode resistance

y?

Earth fault loop impedance test

y?

Òperation of residual current devices

y?

Prospective fault current

y?

Site applied insulation and insulation of non conducting floors and walls

u The tests an appliance is required to undergo will depend on the type of appliance, it's electrical slass and subject to a risk assessment by the technician. ie it may not be safe to perform a leakage current test which powers up the appliance, such as a grinder, if it can not be secured to a bench; an insulation resistance test may be a safe option.    s   u The equipment shall have a measured resistance of the protective earth circuit, or the earthing conductor of an extension cord or appliance cord set, which does not exceed 1ɏ.[8] Testing is performed using an ohmmeter or PAT tester;

y?

Šsing the ohmmeter to produce a reading;

y?

Šsing a PAT tester under the following conditions; ‘? 12Ö maximum, test current range 100mA to 200mA - commonly known as "earth

continuity test" or "screen test" and/or ‘? 12Ö maximum, test current 10A - commonly known as "routine test" and/or ‘? 12Ö maximum, 1.5 times rated current of appliance or 25A, which ever is greater -

commonly known as "type test" or "bond test". The choice of which test(s) to use is at the operator's discretion as there is merit in each test for given situations, however the "routine test" is seldom used by competent persons as it simply replicates existing conditions for the (240Ö/10A) appliance and therefore the results are regarded as being of little test value.   ð   O u A leakage current test performed at rated voltage with values not exceeding 5mA for slass I appliances or 1mA for slass II appliances.[9] Alternatively, measure insulation resistance values do not exceed 1Mɏ for slass I and slass II appliances at 500 Ö d.c. or alternatively, to avoid the equipment apparently failing the test because the metal oxide varistors (MÒÖs), or electro-magnetic interference (EMI) suppression has triggered, for equipment containing voltage limiting devices such as MÒÖs, or EMI suppression, at 250 Ö d.c.[10] Leakage surrent testing is performed using a PAT by applying a nominal voltage to the live conductors (active and neutral) of an appliance, and placing 0 volt reference on the earthed parts of a slass I appliance or the external metal parts of a slass II appliance; y?

ominal voltage is 230Ö As. (therefore it can not be performed with a digital multimeter)

Insulation Oesistance testing is performed using an ohmmeter or portable appliance tester by applying a nominal voltage to the live conductors (active and neutral) of an appliance, and placing 0 volt reference on the earthed parts of a slass I appliance or the external metal parts of a slass II appliance; y?

ominal voltage is 500Ö d.c (250 Ö d.c. may be used for equipment containing MÒÖs / EMI filtering)

A deficiency of the Insulation Oesistance (500Ö/250Ö d.c) test is that the d.c voltage will not activate electromagnetic switches or internal relays etc that are common in many modern power tools, computers, TÖs etc and therefore it can only test the appliance up to that point. Appliances with these components / design should be tested used the leakage current test.     s

Polarity testing is a simple test that can be carried out using an ohmmeter or PAT to determine whether the active and neutral of the plug end are correctly connected to the corresponding terminals at the socket end. [11] ote: The earth is tested during the earth continuity test.     y?

The order (polarity) of the pins of a three pin flat pin plug, to their connections, shall be Earth (radial pin ʹ green/yellow wire), eutral (light blue wire) and then Active (brown wire), in a clockwise direction, when viewed from the front of the plug looking at the pins.[12]

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The order (polarity) of the socket apertures of a three pin flat pin socket, to their connections, shall be Earth (radial pin ʹ green/yellow wire), Active (brown wire) and then eutral (light blue wire), in a clockwise direction, when viewed from the front of the socket looking at the apertures.[13]

  Osc     There are two tests methods to be used;       This test requires no specific test equipment and only basic training; y?

The technician shall press the Osc ͞Test Button͟ and note the device trips ͞without undue delay͟.

      This test requires specialised test equipment, knowledge and training; y?

A current, equal to the rated tripping current, shall be ͞suddenly͟ applied between active and protective earth and the operating time measured[14] with maximum trip time 40ms for Type I and 300ms for Type II.

In addition to this, many technicians also test; y? ‘? §?

using 1/2 (half) the rated tripping current to detect nuisance tripping.

§?

using 5 times rated tripping current, with trip times reduced accordingly, to simulate high current exposure.

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under 0 degree and 180 degree phases

Best Practice is to test the Osc under 1/2, 1X and 5X rated tripping current, each at both the 0 degree and 180 degree phases.   O  

Table 4 of the Standard defines inspection and testing intervals for electrical equipment. In general, they range from 6 months to 60 months and are based on the type of appliance, slass and environment it is normally used in. However, these are guidelines only and subject to a risk assessment. Oegulatory authorities, other Standards, workplace safety requirements or manufacturers͛ instructions may specify intervals appropriate to particular industries or specific types of equipment ie construction and demolition sites require three monthly retest intervals for all electrical appliances used on-site.   O  
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rollowing testing, compliant equipment shall be fitted with a durable, non-reusable, non metallic tag or other indicator that shall include(a) the name of the person or company who performed the tests; (b) the test or inspection date, and may also include a re-test date.[15] Where in-service inspection or testing identifies equipment which fails to comply with the inspection and/or testing criteria, the equipment shall be appropriately labeled to indicate that the equipment requires remedial action and warn against further use, and withdrawn from service. The choice of remedial action, disposal or other corrective action shall be determined by the owner or the person responsible for the safety of the site.[16] Most tags are applied approximately one hand span away from the plug end of the flexible supply cord to avoid handling damage and stress point loosening. The tag can be applied to the body of an appliance if needed.   O  

There is no specific requirement under the Standard to keep records of inspection and test results aside from the application of tags. The Standard notes:[17] 2.5.1 Where records of test and inspection are kept, the following should be recorded: (a) A register of all equipment;

(b) A record of formal inspection and tests; (c) A repair register; (d) A record of all faulty equipment showing details of services or corrective actions. ÒTE 1 Electrical and/or occupational health and safety regulators may require documentation to be kept in some or all cases. ÒTE 2 Where organizations perform voluntary additional inspections and tests, records of such should be kept. 2.5.2 Where records are kept, they should be retained for seven years, or such period as required by the specific regulations. 2.5.3 Where a risk assessment has been performed in accordance with slause 2.1.1, all documentation shall be retained for seven years or such period as may be required by the relevant Oegulator.