4.3 Initial Verification: Requirements & Process

What Is Initial Verification?

Initial verification is the process of confirming that a new installation — or new work added to an existing installation — is safe and complies with BS 7671:2018+A4:2026 before it is energised and put into service. It is the first inspection and testing of a new installation and results in the issue of an Electrical Installation Certificate (EIC) (covered in Chapter 3).

Initial verification differs from periodic inspection (covered in Chapter 10), which assesses an installation already in service for continued safety over time.

Regulation 641.1 sets the requirement and its timing: every installation shall, during erection and on completion before being put into service, be inspected and tested to verify, so far as is reasonably practicable, that the requirements of BS 7671 have been met. The phrase during erection is the part candidates miss. Some things can only be verified while the work is open — cables before they are buried in a wall or covered by a screed, conduit and trunking before a ceiling is closed in, joints before they are made inaccessible. An inspector who arrives only on the day of handover cannot verify those items and can only record them as a limitation, which is exactly the outcome the regulation is written to prevent.

The qualifier so far as is reasonably practicable is also deliberate. It acknowledges that some verification is impossible without dismantling the installation, and it is the basis on which sampling and limitations are justified — not a general licence to skip work that is merely inconvenient.

The Two-Phase Process

Initial verification has two distinct phases, carried out in a strict order:

Phase 1: Inspection (Visual)

The visual inspection (covered in Section 4.2) is completed first, before any testing. No test instrument is connected until the visual inspection has confirmed the installation is safe to test. A serious visual defect — a disconnected protective conductor, a damaged cable, a missing barrier — means testing should not proceed until the defect is corrected.

Phase 2: Testing

Testing follows a defined sequence: dead tests first, then live tests. The full test sequence is detailed in Chapter 5, but the principle is critical here:

• Dead tests (continuity of protective conductors, continuity of ring final circuit conductors, insulation resistance, polarity verified dead) are performed before the installation is energised. These confirm the installation is safe to switch on.
• Live tests (prospective fault current, live polarity check, earth fault loop impedance (Zs), RCD operation) are performed after energising, because they require the supply to be connected.

The order is not arbitrary. Dead tests protect both the tester and the equipment: applying voltage to an installation with a short circuit or a disconnected protective conductor could cause damage, fire, or electric shock.

Requirements Before Energising

The installation must meet these conditions before it is connected to the supply:

When a Test Fails

A failure part-way through the sequence is not simply corrected and ticked. Regulation 643.1 requires that where any test indicates a failure to comply, that test and every preceding test whose result may have been influenced by the fault shall be repeated after the fault has been rectified.

The reasoning is that an earlier reading taken through a defect is not a valid reading. If insulation resistance fails because a line conductor is in contact with a protective conductor, the continuity results taken before it were measured through that same unintended path and cannot be trusted. Rectify, then go back and repeat.

This is a favourite examiner question because the intuitive answer — "repeat the test that failed" — is only half of it.

What Verification Confirms

Initial verification confirms five things about the installation, as required by BS 7671 Part 6 and GN3 10th Edition (2026):

1. Equipment complies with relevant standards — products are correctly rated, marked, and undamaged.
2. Correct selection and erection — cable sizes, protective devices, and accessories are appropriate for the design and installed correctly.
3. Protection for safety is provided — electric shock protection (basic and fault), thermal protection, overcurrent protection, and fault protection (ADS) are all in place and effective.
4. No damage during erection — cables, accessories, and enclosures were not damaged during installation.
5. Test values meet BS 7671 requirements — measured values (continuity, insulation resistance, Zs, RCD trip times) satisfy the relevant limits.

The inspector verifies the installation against three aspects of BS 7671:

• Design — correct cable sizes, protective device selection, coordination, voltage drop, disconnection times.
• Erection — workmanship quality, secure connections, correct routing, proper support.
• Protection — against electric shock, thermal effects, overcurrent, and fault conditions.

Who Can Carry Out Initial Verification?

Initial verification must be carried out by a competent person — someone who has sufficient technical knowledge, training, and experience to perform the inspection and testing safely and accurately. The person who signs the Electrical Installation Certificate takes personal responsibility for the safety of the installation and the accuracy of the recorded test results. This is a significant legal and professional responsibility under EAWR 1989.

The inspector must:

• Have a thorough understanding of BS 7671 and GN3.
• Be familiar with the test instruments and their correct use (GS38 compliant).
• Be able to interpret test results and compare them against BS 7671 limits.
• Have the competence to perform safe isolation.

Two-Phase Process Summary