What This Requirement Covers
Replacing a consumer unit (fuse board) is notifiable work under Approved Document P. A new consumer unit provides improved protection through RCDs and modern MCBs, replacing older fuse wire or rewirable fuse systems.
Key Requirements
When Replacement Is Needed
- The existing consumer unit uses rewirable fuses or cartridge fuses without RCD protection
- The consumer unit does not have adequate capacity for new circuits (EV charger, heat pump, extension)
- An EICR recommends replacement due to age, condition, or non-compliance
- The existing consumer unit is not a metal (non-combustible) enclosure
Key Requirements
- The new consumer unit must be constructed of non-combustible material (metal enclosure) per Amendment 3 to BS 7671
- All circuits must be provided with RCD protection (30 mA); typically achieved with a split-load board using one or two RCDs, or individual RCBOs
- Circuit labelling must be clear and accurate
- The installation must be tested and an Electrical Installation Certificate (EIC) or Minor Works Certificate issued
- The earthing and bonding must be checked and upgraded if necessary
RCBO vs Split-Load Consumer Units
- Split-load board: Circuits divided between two RCDs; if one RCD trips, half the circuits lose power
- RCBO board: Each circuit has its own RCBO (combined MCB and RCD); if one trips, only that circuit is affected. More expensive but more reliable
- RCBO boards are increasingly specified for new installations due to their selective fault protection
Practical Compliance Tips
- Consumer unit replacement is notifiable; use a competent person scheme registered electrician
- Specify an RCBO board for better fault discrimination (individual circuit protection)
- The electrician should test the entire installation (not just the new consumer unit) and issue an EIC
- Ensure the main bonding connections are checked and upgraded if necessary
- Label all circuits clearly; unclear labelling is a common deficiency found in EICRs
- The replacement typically takes 4-8 hours and costs GBP 500-1,200 depending on the number of circuits
- Keep the EIC with the property documents; it is required for property sales and rental compliance