London Consumer Unit Upgrade — 18th Edition, RCD, AFDD, Part P

Upgrading a consumer unit (fuseboard) is one of the most routine London electrical jobs — and the most commonly misunderstood. Under BS 7671 18th Edition Amendment 3, a consumer unit must be metal-cased (post-2016 rule — plastic boards in domestic settings are non-compliant for new installations), must provide 30 mA RCD protection on every socket circuit and every lighting circuit serving accessible locations, and must meet short-circuit fault ratings compatible with the incoming supply.

AFDD (Arc Fault Detection Device) protection is a strong recommendation on all circuits feeding socket outlets and is mandatory on new builds and HMOs in many London boroughs. BSI and the IET have been pushing toward full AFDD adoption in 18th Edition Amendment 4 drafts.

Part P applies — consumer unit replacement is unambiguously notifiable. Certification via a competent-person scheme (NICEIC, NAPIT, Stroma, ELECSA) is the standard route. The job itself takes 4-8 hours for a 10-14-way board in a typical Victorian terrace.

AskBaily routes London consumer unit upgrades to Part P competent-person-scheme electricians who specify the correct short-circuit-rated board, RCBO per circuit, and AFDD where required.

Consumer unit compliance checklist

• Metal case. Post-2016 requirement. Plastic boards non-compliant for new installs.
• RCD protection. 30 mA on every socket circuit and accessible lighting circuit.
• RCBO. Per-circuit protection preferred over split-load RCD boards to avoid cascade tripping.
• AFDD. Mandatory on HMOs and new builds in some boroughs. Strongly recommended everywhere.
• Short-circuit rating. Board must match incoming supply fault level.
• Part P. Competent-person scheme certification. NICEIC, NAPIT, Stroma, or ELECSA.

Frequently asked questions

Is my old plastic consumer unit still legal? Pre-existing plastic boards installed before the 2016 rule are not retroactively illegal — but they cannot be like-for-like replaced. Any replacement must be metal-cased to BS 7671 18th Edition.

What is an RCBO and why should I specify it? RCBO combines an MCB (overcurrent protection) with an RCD (residual-current protection) in a single per-circuit device. A trip on one circuit does not cascade to adjacent circuits — unlike split-load RCD boards where one fault kills multiple circuits.

How much does a London consumer unit upgrade cost? £500-£1,500 for a typical 10-14-way board in a 3-bed terrace. £1,500-£3,000 for larger boards with AFDD, surge protection, and multi-zone RCBO.

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