Factory office keeps tripping: corroded isolator switch

The breaker kept tripping on and off in a factory estate office. Degraded wiring was the suspicion, which meant a full cable run replacement. But the wiring sits inside conduit and protected, while the outdoor isolator switch sits exposed, and that detail changed everything.

By Team Snowflake | Updated 28 Jul 2026

Case summary

Panasonic Wall-mounted14 years oldIndustrialSungei Kadut, Singapore

Concern: The operator faced replacing the entire cable run from the DB board out to the outdoor unit, a major job.
Found: Corrosion at the isolator's cable-gland entry point, where moisture had wicked in along the cable sheath, causing on-and-off trips.
Key check: Opened the isolator and checked the cable-gland entry point before testing the compressor or replacing the outdoor unit.
Result: The trips stopped completely. The unit ran through a full afternoon under steady load with no breaker faults. The conduit wiring stayed in place, so the costly cable replacement was never needed.

What we were told

The office aircon keeps tripping the breaker, on and off with no clear pattern. A quote to rip out and replace the whole power cable run has already come in. That is a big job for a tripping breaker.

What we checked

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.

The trips came and went, and worsened on humid afternoons.
The isolator casing showed external corrosion and discolouration.
Opened up, the corrosion was concentrated at the cable-gland entry point, not on the switch contacts themselves.
The wiring run from the DB board through conduit tested normal, with no degradation, which ruled the cable out entirely.

What we found

Years of moisture and airborne chemical fumes had let corrosion build at the isolator's cable-gland entry, where the power cable enters the box. Moisture had wicked in along the cable sheath at that entry point, not through the switch contacts themselves. That weakened connection heated up under compressor load, and once it heated enough, the breaker tripped. On humid days the corrosion let more moisture through, 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.

What fixed it

We set out two options. The first was to reseal the existing cable-gland entry as a short-term fix. The second was to replace the cable gland with a fully sealed industrial-rated entry point, along with a fresh weatherproof isolator box. The original residential-grade isolator was never suited to a factory wall exposed to fumes and moisture. With fourteen years of corrosion at that entry, resealing alone would have bought only a few months. The full replacement was the lasting fix. After fitting it, we ran the unit under sustained compressor load and confirmed the connection stayed cool and stable throughout.

Outcome

The trips stopped completely. The unit ran through a full afternoon under steady load with no breaker faults. The conduit wiring stayed in place, so the costly cable replacement was never needed.

What this case teaches us

An exposed switch fails before protected wiring does

Trips that worsen in humid weather point to a weak connection where the cable enters the isolator, not the wiring deep inside the unit.
The outdoor isolator sits on the wall with no cover. In a factory estate, fumes and moisture corrode its entry points long before conduit-protected cable fails.
A full cable run replacement is a major job. Ask which parts are exposed and which are protected before agreeing to it.

Questions this case answers

Aircon tripping the breaker on and off in a factory unit: why?

Start at the most exposed point on the power path. At this Sungei Kadut office the outdoor isolator sat on the wall with no cover, and its cable-gland entry had corroded after years of moisture and airborne chemical fumes. That weakened connection heated up under compressor load until the breaker cut out.

Trips get worse on humid afternoons. Does that mean anything?

It narrows the search considerably. Moisture had wicked in along the cable sheath at the gland entry, so damper air let more through and the trips spiked. The run from the DB board through conduit tested normal, which is what conduit is for. Exposed hardware degrades long before cable shielded from the same air.

Is a residential isolator suitable on a factory wall?

Not for that exposure. The original here was residential-grade, sitting on an outer wall facing fumes and moisture for fourteen years. Resealing the existing gland was offered as a short-term option, but with corrosion that far along it would only have bought a little time. A sealed industrial-rated entry and weatherproof box was the lasting fix.

How do I know it is the switch and not the wiring?

Ask which parts are exposed and which are protected. Opening the casing here put the corrosion at the cable-gland entry rather than on the switch contacts themselves. After the replacement, the unit ran under sustained compressor load with the connection staying cool and stable, and the conduit wiring never came out.

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