Part P Consumer Unit Replacement 4

Question 1

What is the recommended height for the consumer unit main switch in a domestic installation per accessibility guidance?

Accepted Answer

1.35–1.5 m above finished floor level (to the centre of the main switch operating mechanism)

Answer

Accessibility guidance (BS 8300 and NHBC) recommends the consumer unit main switch be at a height (typically 1.35–1.5 m to the switch centre) where it can be reached by most users, including those with limited mobility.

Question 2

What information must the circuit chart inside the consumer unit show?

Accepted Answer

Each circuit's purpose, cable reference method, protective device type and rating, and RCD assignment

Answer

BS 7671 Regulation 514.9.1 requires a circuit chart (schedule) to be fixed at or adjacent to the consumer unit, showing each circuit's purpose, protective device details, cable size/reference method, and RCD or RCBO assignment.

Question 3

What is the first step when replacing a consumer unit safely?

Accepted Answer

Isolate the supply at the cut-out (service fuse) — which requires the electricity supplier's presence or a service cut-out sealing tool — and prove dead before any work begins

Answer

The supply must be isolated at the cut-out (supply fuse) to make the meter tails and main switch terminals dead before they can be safely disconnected; this requires the electricity supplier to attend or a licensed operative with a sealing tool.

Question 4

What are 'meter tails'?

Accepted Answer

The cables connecting the electricity meter to the consumer unit main switch — typically 25 mm² or 35 mm² insulated single-core cables

Answer

Meter tails are the single-core insulated cables connecting the electricity supplier's meter to the consumer unit main switch; they are live when the supply is connected and typically 25–35 mm² cross-section for a standard 100 A supply.

Question 5

Can the meter tails be extended or modified by an electrician during consumer unit replacement?

Accepted Answer

Meter tails can be extended or modified by a DNO-registered or competent electrician, but the service fuse and supply-side equipment must not be touched without the DNO's involvement

Answer

Meter tails (between meter and consumer unit) are within the scope of the customer's installation and can be modified by a competent electrician; however, the supply-side (service cable, cut-out and meter) must not be interfered with without the DNO's permission.

Part P Electrical Practice Test

Part P Electrical Practice Test

Part P Consumer Unit Replacement 4