18th Edition Consumer Units: What Electricians Need to Know

The 18th Edition of the Wiring Regulations (BS 7671:2018 + A2:2022) changed what electricians need to specify for consumer units — and two years on, there's still confusion about when arc fault detection (AFDD) is actually required.

Here's what you need to know before you quote your next domestic rewire.

What changed in the 18th Edition?

The headline change was the introduction of AFDD (Arc Fault Detection Devices) as a required protection measure in certain circuits. Regulation 421.1.7 requires AFDD in:

• Final circuits in domestic premises supplying socket outlets rated up to 20A
• Final circuits in bedrooms of certain premises
• Single-family homes where the wiring is concealed in walls at a depth of less than 50mm
• High-risk locations — temporary structures, locations where livestock is kept

The purpose is to detect series arcing faults, which cause around 4,000 house fires per year in the UK but aren't detected by conventional MCBs or RCDs.

Does every rewire need AFDD?

No — and this is where the confusion arises.

The regulations allow a risk assessment approach. Reg 421.1.7 states AFDD is recommended in the above locations but an assessment can conclude it isn't needed if other measures are in place. In practice, many electricians and Part P inspectors are requiring AFDD on all final circuits in domestic rewires to ensure full compliance.

The short answer: if you're doing a full rewire and want a straightforward sign-off, specify AFDD boards. If you're doing a partial rewire or consumer unit change-only, discuss with your inspector first.

Which consumer units do we stock?

At APM, we carry consumer units to cover all domestic scenarios:

FuseBox (our top pick for 18th Edition compliance)

FuseBox makes some of the most competitively priced AFDD-ready boards on the market. Their F100SPD range includes Type 1+2 surge protection as well as dual RCD protection — both now required under the 18th Edition — and AFDD add-ons are available.

FuseBox F100SPD10AFDD — 10-way, dual RCD + SPD + AFDD on all circuits. Current price: £75.80 — significantly below Toolstation (£112.99 for a comparable Axiom board).

FuseBox boards have straightforward labelling, easy busbar connections, and their customer technical support is responsive — relevant when an inspector queues a question.

MK Sentry

The MK Sentry range is a solid mid-market choice. Well-made, readily available, and familiar to most inspectors. We stock 10-way and 12-way dual RCD configurations. AFDD upgrades are available as separate devices.

Wylex

The Wylex NHRS range remains popular for straightforward replacements. If the existing installation uses Wylex MCBs, a like-for-like board swap is often the cleanest option.

Type A vs Type B RCDs — don't get caught out

The 18th Edition also tightened requirements around Type A RCDs for circuits supplying EV chargers, heat pumps, and inverter-driven appliances. Type AC RCDs (which only detect sinusoidal AC fault currents) are no longer sufficient for these circuits.

If your domestic customer has or is planning an EV charger, specify a board with Type A RCDs on the relevant circuits. FuseBox and MK both supply Type A variants.

In-store and online

All the boards mentioned above are in stock at our trade counter in Acton, W3 7TZ. We can also cut cable and supply MCBs, RCBOs, and SPDs separately if you're doing a board upgrade rather than a full rewire.

Order online at apmi.uk or call APM for help choosing the right consumer unit on 020 8702 8080 — if you're not sure which board to specify, our counter staff can talk it through.