Intermittent trips traced to corroded isolator in industrial setting
Aircon case in Sungei Kadut, Singapore: electrical/control traced to outdoor isolator switch contacts corroded from long exposure to moisture and fumes. This caused on-and-off trips after targeted diagnosis checks.
Case details
What client reported
The aircon in the office keeps tripping the breaker. A contractor came and said the wiring from the DB board to the outdoor unit has gone bad. He blamed the factory setting and said the whole cable run needs to be replaced.
What we found
On-and-off trips in a factory setting need a check at the point most exposed to the air. The isolator switch sits outside on the wall, open to fumes and moisture.
- Trip pattern was on and off, and worsened during humid conditions.
- Isolator switch casing showed visible signs of corrosion on the outside.
- Internal contacts were pitted and stained from chemical exposure.
- Wiring run behind the isolator tested within normal resistance range.
The isolator switch contacts had corroded from long exposure to moisture and airborne chemical residue. The corroded contacts created high resistance under compressor load current. This caused the breaker to trip on and off. The wiring itself was intact throughout the run.
What we did
The wiring does not need replacing. The fault is at the isolator switch. Corroded contacts are creating the resistance that causes trips. Swapping the isolator with a rated unit for harsh settings fixes the issue. We retest under full load after fitting.
After the corroded isolator was swapped, the trips stopped fully. The unit ran under steady load with no breaker faults. No wiring work was needed.
Timeline
Day 1
On-and-off breaker trips reported in factory estate office.
Day 3
Opened and checked the isolator switch contacts before testing compressor or replacing the outdoor unit.
Day 3
Corroded isolator swapped and unit retested under load. Trips stopped.
What we learned
Why factory setting trips often start at the isolator.
- Isolator switches in factory zones are exposed to moisture, chemical fumes, and fine dust. These corrode the internal contacts over time. Wiring behind the switch is usually shielded inside trunking or conduit.
- Corroded contacts create resistance under load. This causes on-and-off trips that look like a wiring or compressor fault. The trips stop once the isolator is swapped.
- Opening the isolator casing and checking the contacts is the right first step. Do this before condemning the wiring run or testing compressor health.
Best next step
If your unit is behaving similarly, start with the service path that fits this case before approving broader scope.
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