Solar Panels Tripping Your Electrics? RCD and Breaker Fixes

Your solar system is running fine, then suddenly the lights go out or your kitchen sockets go dead. You head to the consumer unit and find a switch in the tripped position. Before you start flicking it back repeatedly, it is worth understanding what tripped and why — because resetting without investigation can be a genuine safety risk.

RCD, MCB, RCBO: what tripped and what it means

Your consumer unit (fusebox) is likely to contain three types of protective device. Each trips for a different reason.

RCD (Residual Current Device) detects earth leakage current — electricity that is flowing where it should not, such as through a person or through a fault to earth. RCDs protect people. When an RCD trips, the cause is almost always some form of earth fault or unwanted current path, and it should be taken seriously.

MCB (Miniature Circuit Breaker) detects overcurrent — a circuit drawing more electricity than it was designed to carry. MCBs protect wiring. If your solar MCB trips, the circuit may have been short-circuited or overloaded.

RCBO (Residual Current Breaker with Overcurrent protection) combines both functions in a single device. It trips for earth leakage or overcurrent. A well-installed solar system should have its own dedicated RCBO, so that a fault on the solar circuit does not affect the rest of your home.

If you are not sure which device tripped, look at the labels on your consumer unit. The solar circuit should be labelled, though some older installations are not.

Cause 1: Your solar circuit shares an RCD with other circuits

This is the most common cause of solar-related trips affecting other parts of your home. When a solar system is added to an existing consumer unit, it is sometimes connected to a shared RCD that also protects your kitchen sockets, lights, or other circuits. If the solar side develops even a small amount of earth leakage, the shared RCD trips — and everything downstream goes off at once.

The correct approach under BS 7671 (the UK wiring regulations) is for the solar circuit to have its own dedicated RCD or RCBO, completely separate from your household circuits. That way, a solar fault only affects the solar circuit, not your whole ground floor.

If your solar system was installed recently and this keeps happening, it is worth asking your installer to confirm the circuit protection arrangement.

Cause 2: Moisture ingress

Solar systems live outdoors, and moisture can find its way in through DC connectors (the click-together plugs that join panel strings to the inverter cable run), cable penetrations through the roof or wall, or junction boxes. When water reaches a live conductor, it creates a path for current to leak to earth — exactly what the RCD is designed to detect.

This type of trip is more common after heavy rain, during humid weather, or in winter when condensation builds up. If your trips seem to follow wet weather, moisture ingress is a likely culprit.

Diagnosing this properly requires a qualified electrician or installer with the right test equipment. Do not attempt to open DC connectors yourself — DC circuits from solar panels are live whenever there is daylight and cannot be switched off safely without the correct isolators.

Cause 3: Degraded cable insulation

The DC cables running from your roof panels down to the inverter are rated for outdoor UV exposure, but they are not indestructible. Over time, UV damage can crack or harden the outer sheath, especially on cables that were not properly clipped or were left running in direct sun without conduit protection. Rodents will also chew through cables given the opportunity.

Damaged insulation can allow leakage current to earth, causing the RCD to trip. This type of fault tends to get worse over time rather than clearing itself, and affected cables need to be inspected and replaced.

If your system is more than five or six years old and you have never had the DC cabling checked, it may be worth asking an installer to carry out a visual inspection, particularly in the roof space.

Cause 4: Inverter internal earth fault

The inverter itself can develop an internal fault that causes earth leakage current. Most modern inverters run self-diagnostic checks and will display an error code or fault light when this happens — check the display panel or your monitoring app for any fault codes.

An inverter earth fault typically cannot be fixed at home. If the inverter is still within its warranty period (usually five to twelve years depending on the manufacturer), contact your installer or the manufacturer directly to arrange a warranty assessment. Do not attempt to open the inverter casing.

Cause 5: Nuisance tripping on high-generation days

If your trips happen specifically on bright sunny days when your panels are producing well, the cause may be the type of RCD fitted to your consumer unit rather than an actual fault.

Solar inverters produce a small DC component in their output current. Older Type A RCDs are not designed to detect this and can react unpredictably to it, sometimes tripping when no real earth fault exists. This is known as nuisance tripping.

Modern installations should use Type B RCDs or Type A-SI (Superimposed) RCDs, which are designed to handle the DC component produced by solar inverters. If your system was installed on an older consumer unit with standard Type A devices, upgrading to the correct RCD type may resolve the problem entirely. This is a job for a qualified electrician.

Cause 6: Too many circuits on one RCD — cumulative leakage

Even without an actual fault, it is normal for each circuit in your home to have a tiny amount of earth leakage current. Individually, these amounts are well below the RCD trip threshold. But if too many circuits are all connected to the same RCD — which can happen when a solar circuit is added to an already-busy consumer unit — the combined leakage from all those circuits can exceed the trip threshold, even though none of them individually has a fault.

Adding a solar circuit to an existing busy RCD group can push the cumulative leakage just over the edge. The solution, again, is a dedicated RCBO for the solar circuit, separating it from all other household circuits.

What to do when it trips

1. Look before you reset. Check whether any error codes are showing on the inverter display or your monitoring app. Note the time and weather conditions — this information will help diagnose the cause.
2. Reset once. Flip the tripped device back to the on position. If it holds, monitor the system over the next few hours.
3. If it trips again, stop. Do not keep resetting. Contact your solar installer or a qualified electrician. Describe what you observed: which device tripped, what time, what the weather was like, and whether any error codes appeared.
4. If it trips immediately on reset, or if you notice any burning smell, discolouration, or visible damage near the consumer unit or inverter, do not reset it. Call an electrician.

The proper fix

In most cases where a solar system is repeatedly tripping household circuits, the underlying answer is the same: the solar circuit needs its own dedicated RCBO of the correct type (Type B or Type A-SI), with no other circuits sharing it.

This is what should have been done at the time of installation under current wiring regulations. If it was not done, or if the wrong type of device was fitted, an electrician can usually correct it in a single visit.

The cost of fitting a dedicated RCBO is typically in the region of £50 to £150 for the labour and parts, depending on your consumer unit and location. It is a small outlay compared to repeated call-outs or the inconvenience of ongoing trips.

If you are still within the warranty or guarantee period of your solar installation, contact your installer first — this kind of correction should arguably have been part of the original installation.

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