Why Does My Solar System's RCCB Trip When It Rains? Causes and Solutions

What Is an RCCB and Why Does It Trip?

A Residual Current Circuit Breaker (RCCB) — sometimes called an RCD — is a safety device in your electrical switchboard that protects against electric shock and earth leakage faults. It continuously measures the difference between current flowing in and out of a circuit. If that difference exceeds a safe threshold (typically 30 mA for residential systems), it trips and cuts power to that circuit within milliseconds.

In solar systems, the RCCB on the AC output of your inverter is a mandatory safety requirement in Singapore under SS638 / SS551 and EMA regulations.

Why Does Rain Trigger RCCB Trips?

This is one of the most common after-installation questions from Sunollo customers. Rain can cause RCCB trips for several reasons:

1. Earth Leakage Current from DC Cables

Solar DC cables run along your roof and are exposed to weather. When panels and cables get wet, small amounts of current can leak from the DC circuit to earth — especially if cable conduits have imperfect sealing or small abrasions. Even 15–30 mA of leakage can trip a sensitive RCCB.

Is it dangerous? Occasional minor leakage from wet cables is common and the RCCB is doing its job. However, persistent leakage or leakage that increases over time can indicate damaged cable insulation — which should be inspected.

2. Ground Leakage from the Inverter During Rain

Some inverters — particularly transformer-less (TL) models — can develop higher earth leakage when the internal temperature changes rapidly during a rain event. This is a known characteristic and manufacturers account for it, but very sensitive RCCBs can still trip.

3. Condensation Inside Junction Boxes

If roof junction boxes or MC4 connectors are not properly sealed, rain can cause condensation or water ingress, creating a leakage path to earth. This is a more serious cause and requires inspection.

4. Nuisance Tripping from Inverter Capacitance

Transformer-less inverters produce a small but measurable capacitive leakage current as a by-product of their design. When this combines with additional leakage from wet conditions, the total may exceed the RCCB trip threshold. This can sometimes be resolved by installing an RCCB with a higher immunity rating or by checking the inverter's built-in earth leakage protection settings.

Is It Safe to Reset the RCCB After Rain?

In most cases, yes — once the rain stops and the system has had 15–30 minutes to dry, you can reset the RCCB. Here is the correct procedure:

1. Wait until the rain has fully stopped and the intensity on the roof has reduced.
2. Go to your electrical switchboard. Locate the RCCB labelled for your solar system (usually labelled "Solar" or "PV" or by your electrician at installation).
3. Push the RCCB lever fully down first, then push it back up to reset. Some RCCBs have a separate reset button.
4. Your inverter will restart automatically within 1–5 minutes and begin generating once sunlight is sufficient.
5. Check your monitoring app to confirm the system comes back online.

Do not reset if:

• The RCCB trips again immediately after resetting — this indicates an active fault that needs professional inspection.
• You smell burning or see any signs of physical damage near the switchboard or on the roof.
• The trip happens in dry weather with no obvious trigger.

How Often Is "Too Often"?

An occasional trip (once or twice a year during exceptionally heavy rain) is generally acceptable. If your RCCB is tripping:

• Every time it rains — your system needs an inspection. Common causes include poor cable sealing, degraded insulation, or an incorrectly specified RCCB.
• More than 3 times in a month — contact Sunollo for a site visit.
• In dry weather — treat this as an urgent fault and do not reset repeatedly; call Sunollo.

Long-Term Solutions Sunollo Can Implement

• Inspection and re-sealing of all DC cable conduits, junction boxes, and MC4 connectors on the roof
• Upgrading the RCCB to a type specifically rated for solar inverter installations (Type B or Type A with higher immunity)
• Adjusting the inverter's internal earth leakage compensation settings (where supported by the manufacturer)
• Installing a dedicated DC RCCB where applicable, separating DC leakage from the AC circuit RCCB

Contact Sunollo

If you are experiencing repeated RCCB tripping, please contact us at hello@sunollo.com or call us. We will conduct a full leakage current inspection and advise on the best remediation.