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Frequently Asked Questions: Inspection and testing

What qualifications do I need to carry out inspection and testing?

The IET Wiring Regulations does not provide requirements for specific qualifications for electricians, and the IET cannot advise the exact qualifications which are required.

Carrying out an inspection of electrical installations is a complex task, the person carrying out the inspection and testing is required to have comprehensive knowledge and experience of different types of electrical installations.

There is an extra level of qualification and competence achieved, beyond the standard four-year vocational route commonly followed by qualified inspectors and testers.

The HSE uses the term ‘competent person’, the term ‘skilled person’ is used throughout BS 7671:2018, Regulation 134.1.1 states that persons carrying out electrical works shall be skilled, which is defined in Part 2 as;

‘a person who possesses, as appropriate to the nature of the electrical work to be undertaken, adequate education, training and practical skills, and who is able to perceive risks and avoid hazards which electricity can create.’

They are different terms, but they all mean the same thing, the person carrying out the inspection and testing is required to have the correct qualifications, experience and knowledge.

IET Guidance Note 3 provides guidance on inspection and testing.

What is the recommended frequency between inspection and testing?

For new electrical installations, the initial frequencies for inspection and testing will be recommended by the electrical designer. Subsequent intervals will be recommended by the competent person carrying out the inspection and testing.

The interval shall be determined dependant on the type of installation and equipment, its use and operation, the frequency and quality of maintenance and the external influences, to which it may be subjected.

IET Guidance Note 3, Section 3.7, Table 3.2 provides some useful information regarding recommended initial frequencies of inspection of electrical installations. It’s important to note that these are recommendations and not legal requirements, they are intended for the initial.

What test voltage do I use for performing an insulation resistance test?

Where Surge Protective Devices (SPDs) or other equipment are likely to influence the verification test or be damaged, such equipment shall be disconnected before carrying out the insulation resistance test.

Where it is not reasonably practicable to disconnect such equipment (e.g. fixed socket-outlet incorporating an SPD), the test voltage for the particular circuit may be reduced to 250 V DC, but the insulation resistance shall have a value of at least 1 MΩ.

For a circuit with a nominal voltage up to and including 500 V, with the exception of SELV and PELV systems, it requires a test voltage of 500 V DC. Table 64 of BS 7671:2018 provides test voltages and minimum values of insulation resistance.

Do I need to record the resistance value of protective bonding conductors?

In previous editions of BS 7671, a check to verify continuity was only required and a tick inserted in the box. Regulation 643.2.1 of BS 7671:2018 requires continuity of protective bonding conductors to be verified by measurement of resistance.

The table below indicates typical resistances of protective bonding conductors for varying lengths.



Length (M)























What code should I give to observations discovered during inspection and testing?

Any observations noticed by the inspector during the inspection and testing is required to be recorded on an Electrical Installation Condition Report (EICR) and a classification code attributed according to the degree of urgency.

C1 – Danger present. Risk of injury. Immediate remedial action required.

C2 – Potentially dangerous – urgent remedial action required.

C3 – Improvement recommended.

FI – Further investigation required without delay

Carrying out an inspection of electrical installations is a complex task, the person carrying out the inspection and testing is required to have comprehensive knowledge and experience of different types of electrical installations. The inspector will make an engineering judgement to determine the correct classification code.

Guidance on classification codes, can be found in Best Practice Guide (BPG) 4 on the Electrical Safety First website, some trade associations also produce publications providing guidance on coding of observations made during EICR inspections.

What if I discover a defect with the distributor’s equipment whilst carrying out inspection and testing?

The equipment at the intake position is owned by the distributor and the meter and tails belong to the supplier. However, as part of the inspection process, BS 7671:2018 requires the inspector to carry out a visual inspection of the external condition of the distributor’s equipment, to ensure it is safe for continued use.

Examples of distributors equipment requiring inspection:

  • Service cable
  • Service head
  • Earthing arrangement
  • Meter tails
  • Metering equipment
  • Isolator (where present).

The equipment should be inspected for signs of damage or evidence of overheating if a defect is observed the person ordering the report, should be informed immediately and in writing. It is the responsibility of the person ordering the report, to inform the Distribution Network Operator (DNO).

What if I discover an item which is immediately dangerous during an inspection?

If an item is discovered which is immediately dangerous, a classification code C1 should be issued. The person ordering the report is to be advised immediately and followed up in writing (before the report is issued), that immediate action is required (or preferably, has been taken) to remove the danger. In some cases, this could mean isolating the affected circuit.

The inspector must discharge their duty under the Health and Safety at Work Act 1974 and the Electricity at Work Regulations 1989.

Which earth fault loop impedance values should I record on the Electrical Installation Condition report (EICR)?

BS 7671:2018, Tables 41.2, 41.3, and 41.4 indicate the maximum earth fault loop impedance values, it’s important to note that these are the maximum values which should not be exceeded when the cable is at it’s assumed conductor operating temperature (70c).

When carrying out an earth fault loop impedance test at ambient temperature, it is necessary to adjust the value to take into account increased resistance of the conductors due to a rise in temperature caused by load current.

The IET On Site Guide provides tables indicating maximum values corrected to 80 per cent to be used as a quick reference, but for any circuits which are close to or exceed this value, a detailed calculation can be carried out using the maximum values and correction factors in Appendix 3 of BS 7671:2018.

Where the maximum permitted earth fault loop impedance values, stated on the schedule of test results, are taken from a source other than the tabulated values given in Chapter 41 of BS 7671:2018, the source of the data should be identified in the appropriate section of the schedule.