Bugis shophouse trips after rain: sun-cracked cable sheath on the roof

Mitsubishi Heavy Industries Wall-mounted·9 years old·Shophouse·Rochor, Singapore

The shophouse office aircon tripped the breaker twice after heavy rain. On dry days, it could run through normal office hours. The tenant feared the compressor was shorting because the power cut felt sudden and affected work.

We matched the fault to the weather pattern first. A compressor fault can trip power, but rain-linked trips send the inspection outdoors. In a Rochor shophouse, outdoor units sit on rooftops with awkward access, so we checked the roof route, the isolator itself, and the full length of exposed cable before assuming a switch fault.

Years of direct sun and roof heat had dried and cracked the cable's own outer sheath, at the point where the run crossed an open stretch of roof. The isolator enclosure itself was intact and properly sealed. The fault sat in the cable jacket, not the switch. Once the sheath cracked, rain could track along the exposed run and reach a connection point, tripping the breaker. On dry days that same crack carried no moisture, so the unit ran normally, which explained the pattern the tenant saw.

We advised replacing the damaged section of cable with UV-rated cable suited to open rooftop runs, rather than replacing the isolator, which tested sound. The new section was routed to reduce direct sun exposure where the roof layout allowed. We also told the tenant that resetting the breaker after rain was not a safe workaround while the sheath stayed cracked, since moisture would keep finding the same path until the cable itself was replaced. The quote stayed limited to the cable run.