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If you have searched “split load consumer unit” or “dual RCD consumer unit” and landed here, you are probably getting quotes for a consumer unit replacement Aberdeen and wondering what on earth the difference is. That is a completely reasonable question. For years, these two board types were the industry standard, and plenty of websites still talk about them as though they are current, sensible options.
They are not — at least not for a new installation in 2026.
This guide explains what split load and dual RCD boards actually are, why they became the norm, and why the electrical industry has now moved on. We will walk you through why full RCBO boards are the only type Faithful Spark installs, what BS 7671 Amendment 4 means for homeowners in Scotland, and what to do if another contractor is quoting you for something older.
What Is a Split Load Consumer Unit?
A split load consumer unit divides your home’s electrical circuits into two separate banks inside the same enclosure. One bank sits behind an RCD (Residual Current Device), which provides earth fault and shock protection. The second bank connects directly to the main isolator switch, with no RCD sitting upstream of it.
The idea behind the split load design was sensible enough for its time: put the circuits most likely to need RCD protection (sockets, bathroom circuits, outdoor supplies) on the protected bank, and put lighting circuits on the unprotected bank where an RCD was not considered essential. That way, if a faulty kettle tripped the socket bank’s RCD, the lights stayed on. You were not left fumbling around in total darkness.
The problem is that this design leaves a significant portion of your home’s wiring with no upstream RCD protection at all. If a fault develops on a lighting circuit, all you have is the MCB. An MCB responds to overloads and short circuits. It does not protect against the low level earth leakage currents that cause electrocution. Under modern electrical safety standards, that is simply not acceptable for a new installation.
What Is a Dual RCD Consumer Unit?
A dual RCD consumer unit is a step up from the split load approach. Instead of one bank with an RCD and one without, you get two banks each protected by its own RCD. Every circuit in the property has some form of RCD protection upstream of it.
The practical difference from the homeowner’s perspective: if a fault occurs on any circuit, the RCD for that bank trips. Roughly half the house loses power. The other half stays on. It is better than a split load board — you still have some lighting, some sockets — but you are still losing a large chunk of your home’s circuits every time one thing goes wrong.
Dual RCD boards were a real improvement when they were introduced, and they made sense when RCBOs were expensive and installing one per circuit added significantly to the cost of a job. That cost gap has closed considerably. The argument for the dual RCD approach has weakened with it.
The Full RCBO Board: Why It Is the Only Sensible Choice in 2026
An RCBO — a Residual Current Breaker with Overcurrent protection — combines the functions of an MCB and an RCD into a single device. A full RCBO board has one RCBO per circuit. Every circuit has its own individual overcurrent and earth fault protection, completely independent of every other circuit.
The result is straightforward: if a fault trips a circuit, only that one circuit goes off. The rest of the house carries on as normal. Your lights stay on. Your fridge stays running. Your boiler keeps going. Nothing else is disrupted.
There is no shared RCD that can take out half your home. There is no bank arrangement to think about. Each circuit stands entirely on its own.
At Faithful Spark, every consumer unit upgrade in Aberdeen and Aberdeenshire is a full RCBO board as standard. We do not offer split load or dual RCD configurations for new installations. That is not because we are charging a premium — it is because we do not believe in fitting anything to a customer’s home that we would not fit to our own.
Side by Side: What Actually Happens When a Fault Occurs
The table below is the most useful way to understand the real world difference between these three board types. Imagine a faulty kettle develops an earth fault while plugged into the kitchen. Here is what each board type does:
| Consumer Unit Type | What Goes Off | What Stays On |
|---|---|---|
| Split load (1 RCD on socket bank) | All sockets throughout the property | Lighting circuits and dedicated appliance circuits |
| Dual RCD | All circuits on the affected bank (typically half the property) | All circuits on the unaffected bank |
| Full RCBO board | The kitchen socket circuit only | Every other circuit in the property |
The full RCBO board is not even close in terms of fault tolerance. It is the correct approach for any new installation, and it is what Electrical Safety First consistently promotes as best practice for UK residential electrical installations.
Why Both Legacy Board Types Are Now Considered Outdated
The shift away from split load and dual RCD boards is not about fashion or marketing. It reflects a genuine improvement in how we understand fault discrimination in domestic electrical installations.
Fault selectivity is the principle that only the device closest to a fault should operate. In a full RCBO board, that is exactly what happens. In a split load or dual RCD board, a single fault can operate a device that controls far more circuits than the one at fault. That is poor selectivity, and it leads to unnecessary loss of supply to parts of the house that have nothing wrong with them.
Nuisance tripping is also a real problem with dual bank boards. RCDs are sensitive devices. In a house with multiple circuits sharing a single RCD, the cumulative earth leakage from all those circuits adds up. A small amount of leakage on several circuits can combine to trip the RCD even when nothing is actually wrong. Full RCBO boards eliminate this problem entirely because each circuit’s RCBO only responds to leakage on that one circuit.
The surge protection requirement under BS 7671 is another reason a like for like replacement of an older split load or dual RCD board is not straightforward. Amendment 4 has strengthened expectations around surge protection devices (SPDs) for new consumer unit installations. Fitting an SPD alongside a split load board is possible but somewhat pointless when the board itself is already a legacy product. It makes far more sense to install an up to date full RCBO board with a Type 2 SPD as a combined package from the start.
At Faithful Spark, every consumer unit we install includes a Type 2 SPD as standard. The price for a full RCBO consumer unit replacement with SPD starts from £550 + VAT. For a detailed breakdown of what that includes and what affects the final price, see our fuse box replacement cost guide for Scotland.
What About the Cost Difference?
One of the main reasons split load and dual RCD boards remained popular for so long was cost. RCBOs used to be meaningfully more expensive than a standard MCB. Fitting ten RCBOs instead of ten MCBs added a noticeable amount to the material cost of a job.
That price gap has narrowed substantially. Today, the difference between a full RCBO board and a dual RCD board is relatively modest — and in most cases the full RCBO board is the better long term investment for exactly the reasons set out above.
If a contractor is quoting you significantly less for a split load or dual RCD board, ask yourself what you are actually saving. You are getting a board that is already considered a legacy product, with worse fault selectivity, a higher risk of nuisance trips, and a design that does not reflect current best practice under BS 7671 Amendment 4. That is not a saving — it is a compromise you will live with for the next twenty years.
What Does This Mean for EICR Inspections?
An existing split load or dual RCD board will not automatically fail an Electrical Installation Condition Report (EICR) in Aberdeen or Aberdeenshire. The EICR assesses whether an installation meets the standard applicable at the time it was installed, not the standard applicable today. An older board that was correctly installed when it was fitted is not automatically defective.
However, there are important caveats. If your existing board is a very old split load design with no RCD protection on the lighting circuits at all, or if the board is showing signs of age (burn marks, melted insulation, mechanical damage to devices), or if circuits have been added over the years without proper design consideration, an EICR may well recommend an upgrade regardless of the board type.
If you are planning any new circuit additions — an EV charger, a garden power supply, or any other extension to the installation — those circuits must meet current standards, including full RCD protection. In many cases the most practical approach is a full consumer unit replacement at the same time rather than trying to add circuits piecemeal to an older board.
about Faithful Spark Electricians carries out EICR inspections areas we cover and Aberdeenshire and will give you an honest assessment of your existing installation. If your board needs replacing, we will tell you why and quote accordingly — we do not recommend work that is not needed.
Planning an EV Charger or Solar? Your Consumer Unit Matters More Than Ever
If you are considering an EV charger installation in Aberdeen or any other significant new load, your consumer unit is the starting point for the whole conversation. An older split load or dual RCD board may not have the spare capacity, spare ways, or protective device coordination to safely accommodate a 7kW EV charger alongside the existing installation.
Full RCBO boards make this kind of future proofing straightforward. The EV charger gets its own dedicated RCBO. It operates completely independently of every other circuit. If the charger ever develops a fault, it trips its own RCBO and nothing else in the house is affected. That is exactly how it should work.
Adding a new load to a dual RCD board means that new load joins an existing bank, sharing its RCD with multiple other circuits. The potential for nuisance interaction between the EV charger and the rest of that bank is a real consideration that is simply not present in a full RCBO design.
What Certification Does a Consumer Unit Replacement Require in Scotland?
In Scotland, consumer unit replacements are work requiring an Electrical Installation Certificate under the Scottish Building Regulations. Every consumer unit replacement carried out by Faithful Spark comes with a full Electrical Installation Certificate (EIC), issued under BS 7671. This is the document that certifies the work has been designed, installed, and inspected to the current standard.
In Scotland, the relevant framework is the Scottish Building Regulations (Technical Handbooks), with BS 7671 as the technical standard for the electrical installation work itself. Any contractor working in Scotland should be issuing a full EIC on completion — not a self certification notice based on a framework that does not apply in Scotland.
As a NICEIC approved contractor, Faithful Spark is assessed annually against the current edition of BS 7671. Our approval covers all domestic and commercial electrical installation work across Aberdeen and Aberdeenshire.
Frequently Asked Questions
Can I still get a split load or dual RCD board fitted in 2026?
Technically, yes — some contractors will still fit them. We will not. Split load and dual RCD boards are legacy products that do not reflect current best practice under BS 7671 Amendment 4. Fitting one as a new installation in 2026 means fitting something that is already behind the curve before it even goes on the wall. Our position is straightforward: if it is not good enough for our own homes, we are not fitting it in yours.
Will I need to upgrade my existing split load board if I get an EICR?
Not automatically. An EICR assesses your installation against the standard applicable at the time of installation, not today’s standard. An older board that was correctly installed may pass an EICR. However, if you are adding circuits, the new work must meet current standards. And if your board is old enough to show signs of deterioration, an upgrade will almost certainly be recommended on safety grounds rather than regulatory ones.
How much does a full RCBO consumer unit replacement cost with Faithful Spark?
Our consumer unit replacements start from £550 + VAT for a full RCBO board with Type 2 SPD. The final price depends on the number of circuits, access, and any remedial work required on the existing installation. We provide a fixed price at the survey stage — no surprises on the day. See our Scotland fuse box replacement cost guide for a full breakdown of what affects the price.
What is BS 7671 Amendment 4 and does it affect me?
BS 7671 is the IET Wiring Regulations — the technical standard that governs all electrical installation work in the UK. We are now on Amendment 4, which became the mandatory standard in October 2026. Amendment 4 strengthens requirements around RCD protection, surge protection, and fault discrimination. Any new consumer unit installation from October 2026 onwards must meet Amendment 4. If you are planning a consumer unit replacement, make sure your contractor is working to the current amendment — and check they can demonstrate it with the documentation they issue.
Does a new consumer unit add value to my home?
It can, yes — particularly if you are selling and the buyer’s surveyor identifies an outdated or unsafe board. A full RCBO board with SPD is a positive on any survey and removes a potential negotiation point. For a fuller discussion of whether a consumer unit upgrade makes sense for your property, see our guide on whether a consumer unit upgrade in Aberdeen is worth it.
Do I need a new consumer unit before installing an EV charger?
Not always, but often. Whether your existing board can safely accommodate an EV charger depends on its age, condition, spare capacity, and the protective device coordination. We assess this at the survey stage. In many properties, a combined consumer unit replacement and EV charger installation Aberdeenation is the most cost effective approach, both in terms of the work involved and the long term reliability of the installation.
Is a Consumer Unit Upgrade Worth Doing Now?
If your home still has a split load or dual RCD consumer unit, the question is not really whether you should upgrade — it is when. With BS 7671 Amendment 4 now in force, every year that passes is another year of living with a legacy installation that does not reflect current best practice.
Full RCBO boards are not expensive relative to what they deliver. The peace of mind of knowing that a fault on one circuit affects only that circuit — not half your home — is worth a great deal. The additional protection of a Type 2 SPD guarding your appliances, smart home devices, and computers against voltage surges is worth a great deal more again.
For the full picture on whether an upgrade is right for your property, read our consumer unit upgrade guide for Aberdeen and Aberdeenshire. Or if you are ready to get a price, call us on 07304 027013 — we cover Peterhead, Aberdeen, Ellon, Fraserburgh, Inverurie, and the whole of Aberdeenshire.
Call 07304 027013 to Book a Consumer Unit Survey
Faithful Spark Electricians. NICEIC approved. Based in Peterhead, serving Aberdeen and Aberdeenshire. Consumer unit upgrades, EICR inspections, and Electrical Installation Certificates across NE Scotland.
