Aircon Corroded Isolator Tripping Unit

Case Details

What We Checked

• Trip pattern was intermittent and worsened noticeably during humid afternoons.
• Isolator switch casing showed visible external corrosion and discolouration.
• Internal contacts were pitted and coated with chemical residue when opened.
• Wiring run from DB board through conduit tested within normal resistance — no degradation found.

The Diagnosis

Fourteen years of exposure to moisture and airborne chemical fumes had corroded the isolator switch contacts. The pitting created resistance in the power path that increased under compressor load current. When the voltage drop exceeded the breaker's tolerance, it tripped. The wiring behind the isolator was intact — the conduit had protected it from the same exposure.

What Fixed It

We recommended replacing the corroded isolator with an IP-rated unit designed for industrial environments. The standard residential-grade isolator was never suited for a factory estate wall exposed to chemical fumes and moisture. We explained the two options: clean and re-torque the existing contacts as a short-term measure, or swap the entire switch for an industrial-rated enclosure. Given the fourteen years of accumulated corrosion and pitting, cleaning would only buy a few months. The client agreed to the full swap. After installation, we ran the unit under sustained compressor load and measured voltage across the new contacts to confirm zero drop.

The trips stopped completely. The unit ran through a full afternoon under steady load with no breaker faults. No wiring replacement was needed.

Why This Happens

In industrial settings, check the isolator before the wiring.

• Isolator switches sit on the wall near the outdoor unit, fully exposed to moisture, dust, and chemical fumes. Wiring behind them runs inside conduit or trunking, which shields it from the same environment. The isolator is always the most vulnerable point in the power path.
• Corroded contacts add resistance to the power path. Under compressor load current, this resistance causes voltage drops that trip the breaker. The pattern is intermittent and worsens in humid conditions because moisture lowers the surface resistance threshold needed to arc.
• Opening the isolator casing and inspecting the contacts is a two-minute check. It should come before any wiring continuity test or compressor diagnosis in an industrial setting. Ask your technician whether they checked the isolator contacts before quoting cable replacement.
• An IP-rated isolator designed for harsh environments costs a fraction of a cable run replacement. In factory estates with chemical fumes or saltwater exposure, the upgrade pays for itself in avoided downtime within the first year.