Plug-in solar is legal to use in Great Britain, and a compliant kit is designed not to interfere with your RCDs. But the safety charity Electrical Safety First has published advice that goes further than the rules require, and it is worth reading before you order a kit.
What Electrical Safety First says
Its guidance, from technical director Luke Osborne, is that plug-in solar panels “may damage older devices in people’s homes which protect people from electric shock, known as RCDs”. Its recommendation, quoted in full:
“Given unresolved concerns about the potential impact of plug-in solar panels on certain RCDs, we recommend households have at least a Type A bidirectional RCD protecting circuits intended for use with plug-in solar panels. Until these concerns are addressed, homes with Type AC RCDs should not use plug-in solar systems without first upgrading to a minimum Type A bidirectional RCD on those circuits.”
It adds that a plug-in system “should not be connected via extension leads, cable reels, multiway adaptors, travel adaptors or plug-in RCD adaptors”, because those accessories can overheat or become overloaded, and that households should have their electrical installation assessed by a competent electrician registered with a competent person scheme before buying or using a kit.
What “bidirectional” means
Most protective devices are designed on the assumption that power arrives at the line terminals and leaves at the load terminals. Plug-in solar breaks that assumption: the kit pushes power back into the socket circuit. The IET’s Wiring Matters explains the distinction plainly — “a protective device that does not have markings to indicate line and load terminals is a bidirectional device, where power flow in either direction will not cause damage” — and warns that “unidirectional protective devices should not be used for such power sources as the power flow could be in either direction”. Applying a supply to the load side of a unidirectional device can damage its electronics and, in the worst case, disable the residual current protection without any outward sign.
This is a separate question from the RCD type (AC, A, F or B), which is about the shape of the leakage current a device can detect. Our guide to RCDs, DC leakage and plug-in solar covers both, and now includes a section on bidirectional devices.
How to check, and what it can cost
Ideal Home’s renovation and home energy editor, Sarah Handley, described the check on 27 September 2026. Her consumer unit had no label saying whether it was bidirectional, so she photographed the brand names and codes on the RCD and the circuit breakers and looked them up. The result was the word “unidirectional”, and a quoted fix of around £900 to £1,200 to replace the consumer unit — more than the kit itself.
- Open the consumer unit cover and read the labels. Note the manufacturer and the model code on the RCD or RCBOs, and the type letters (AC, A, F or B) if they are printed.
- Look the model up in the manufacturer’s own datasheet. Terminal markings for line and load, or a datasheet that names a supply side, indicate a unidirectional device.
- Have it confirmed. A registered electrician can tell you in minutes what you have and what, if anything, needs changing. Do not rely on a web search alone, and do not start removing covers.
What it means for UK buyers
- This is advice, not law. Nothing in the plug-in solar regulations requires a Type A bidirectional RCD in your home. The government’s product specification puts the duty on the kit: its smooth DC leakage must not exceed 5 mA and it must be designed not to affect upstream RCDs. Electrical Safety First’s position is that this is not yet enough for older installations.
- Check before you buy, not after. A consumer unit upgrade can cost more than the kit, and finding that out afterwards is the expensive order to do it in.
- Never use an extension lead or adaptor to connect a kit, whatever your consumer unit looks like.
- If your installation is old — rewireable fuses, no RCD, no labels, or an unknown age — treat an inspection as part of the cost of the system. See whether you need an electrician.