I’ve got a split load board — what are my actual options?

You’ve been told your split load board is a problem — or you’ve had an EICR that flagged unprotected circuits, and now you’re wondering what to do about it. The honest answer is: you have three options. Not one. And the right one depends on your specific situation, not on whichever is most convenient for the electrician quoting you. Here’s what each option involves, what it costs, and how to decide.

What a split load board actually means

A split load consumer unit has two sides: one protected by an RCD (all circuits on that half trip if a fault is detected), and one side with no RCD protection — just individual MCBs. The unprotected side typically covers circuits added or wired before the 17th Edition wiring regulations made full RCD protection standard practice. Lighting circuits are the most commonly unprotected.

If you want the full background on what RCD protection does and why unprotected circuits carry a higher risk, our guide to RCD protection covers it in detail. For now, the key point is simply this: a split load board isn’t automatically dangerous, but it does mean some of your circuits operate without a meaningful safety net if something goes wrong.

Option 1: Do nothing (for now)

This is the option most people assume they can’t choose — but it’s sometimes the right one. If the following conditions are all true, doing nothing is not irresponsible:

• The installation has been recently inspected and the wiring on unprotected circuits is in good condition
• The unprotected circuits don’t serve bathrooms, kitchens, or other high-risk areas
• You understand the specific risks involved and are making an informed choice, not an uninformed one
• You’re not a landlord (where legal and insurance obligations apply differently)

What matters is that you’re making an informed decision rather than a pressured one. An electrician who gives you the full picture and lets you decide is doing their job properly. One who presents “do nothing” as impossible is not.

Option 2: Partial upgrade — add RCBOs to unprotected circuits

This is the option most people aren’t told about. Instead of replacing the whole consumer unit, individual MCBs on the unprotected side can be swapped for RCBOs — combined MCB and RCD devices that protect each circuit individually, without requiring a new board.

What a partial upgrade involves

• Each unprotected circuit gets its own RCBO replacing the existing MCB
• The board itself stays — no new enclosure, no full rewire of the distribution board
• Typically 2–5 hours of labour depending on the number of circuits
• No Building Regulations Part P notification required if the board itself isn’t being replaced (specific scenarios can vary — confirm with your electrician)
• Cost: roughly £80–£150 per circuit (parts and labour combined), so three unprotected circuits might cost £250–£400 in total

Pros and cons

Pros: Significantly lower cost than full replacement. Less disruption — no full board removal or rewiring of all circuits. Achieves genuine RCD protection on previously unprotected circuits. Per-circuit RCBO protection also means a fault on one circuit won’t knock out the whole board.

Cons: If the board itself is old, cramped, or the existing busbars are worn, individual RCBO swaps may not be physically practical. Worth noting: the 2015 amendment to BS 7671 requires metal enclosures for any new consumer unit installation — a partial upgrade of an existing board doesn’t trigger this requirement, but the plastic enclosure will remain in place.

Option 3: Full consumer unit replacement

Sometimes the right answer is a full board replacement. Not as a default, and not because an unprotected circuit on its own demands it — but because the board itself has reached the end of its useful life, or because the economics of individual RCBO swaps no longer stack up.

When full replacement makes sense

• The existing board is old, cramped, or physically deteriorating
• There are too many circuits to make individual RCBO swaps cost-effective — typically more than six to eight unprotected circuits
• A full rewire is being carried out at the same time anyway
• The plastic enclosure needs to be replaced with a compliant metal-clad unit
• You want RCBO protection on every circuit — not just the previously unprotected ones — which eliminates nuisance tripping across the whole installation

What full replacement involves

• Full isolation, removal of the old unit, installation of a new metal-clad consumer unit
• All circuits reconnected and correctly labelled
• Full testing and Schedule of Test Results
• Electrical Installation Certificate issued
• Building Regulations Part P notification — only NAPIT or NICEIC registered electricians can self-certify; an unregistered electrician would need to notify the local authority separately, which adds delay and cost
• Typically a half-day to full-day job
• Cost: typically £600–£1,100 for a standard domestic property

Making the decision — three questions to ask

Before agreeing to any work on a split load board, ask these three questions. Any competent electrician should answer all of them clearly and without hesitation.

1. How many of my circuits are currently unprotected, and which ones? You should get a specific circuit-by-circuit answer — not a vague reference to “some circuits.”
2. Is a partial RCBO upgrade possible on my board, or is there a specific reason it isn’t suitable? If the answer is simply “we always replace the whole board,” push back on that. There should be a specific technical reason if a partial upgrade isn’t being offered.
3. If you’re recommending full replacement — is that because the board itself is the problem, or just because unprotected circuits need addressing? These are two different justifications, and only one of them necessarily points to a full replacement.

For more on how to tell when a full consumer unit replacement is genuinely warranted — and when it might be a scare tactic — read our consumer unit upgrade guide.