Factory office aircon keeps tripping: corroded isolator switch

Panasonic Wall-mounted·14 years old·Industrial·Sungei Kadut, Singapore

The office aircon keeps tripping the breaker, on and off with no clear pattern. A contractor said the wiring from the DB board to the outdoor unit had degraded in the factory environment. They quoted replacing the entire cable run.

On-and-off trips in an industrial setting narrow to a few likely points along the power path. We started at the outdoor unit and worked inward from the isolator. In a factory estate, the most exposed part usually fails first, and the isolator sits on the outer wall with no cover. We opened its casing before checking the compressor or the wiring run.

Fourteen years of moisture and airborne chemical fumes had corroded the isolator contacts. The pitting created a weak connection in the power path. Under compressor load the weak point drew more, and the voltage drop grew until it crossed the breaker's tolerance and tripped. On humid days the corrosion drew current worse, which is why the trips spiked in the afternoon. The wiring behind the isolator was intact. The conduit had shielded it from the same exposure.

We set out two options. The first was to clean and re-torque the existing contacts as a short-term fix. The second was to swap the whole switch for an IP-rated enclosure built for industrial sites. The original residential-grade isolator was never suited to a factory wall exposed to fumes and moisture. With fourteen years of corrosion and pitting, cleaning would have bought only a few months. The full swap was the lasting fix. After fitting it, we ran the unit under sustained compressor load and checked the voltage across the new contacts to confirm no drop.