This is copied from an article NAPIT did on requirements for replacing consumer units:
Requirements of BS 7671
Replacing a consumer unit is classed as making an alteration and falls into the category of new work. This must be designed, erected and verified in accordance with BS 7671 as required by Regulation 110.1.2 (vi) and the safety of the existing installation must not be impaired, as stated in Regulation 610.4.
Regulation 132.16 states the requirements of additions and alterations. This means existing equipment must be adequate for the alteration. The earthing and bonding must also be adequate for the installation.
The design will also need to consider Regulation 415.1 for additional protection by 30mA RCD and consideration of how to protect against unwanted tripping of the RCD(s) will be needed to comply with the requirements of Section 314, Division of Installation.
Account must also be taken of the manufacturer’s instructions, as required by Regulations 134.1.1 and 510.3.
On completion, identification notices in accordance with Section 514 will need to be fitted and an EIC must be issued in accordance with the requirements of Sections 631 and 632, as stated in Regulation 631.1. Finally, the work must be notified.
Industry best practice
The customer should be encouraged to have an Electrical Installation Condition Report (EICR) carried out before replacing the CU. This will help the contractor to establish that the requirements of Regulation 132.16 have been met to allow the new CU installation to take place. Suitability of the existing earthing and bonding arrangements will be confirmed, as well as the suitability of the DNO’s equipment and meter tails, including polarity of the incoming supply.