This lesson learned supports the safe practice of removing power to a heater circuit whenever the thermal insulation is removed. Ground leakage equipment protection devices limit the energy available under fault conditions. However, the circuits using equipment protection devices are not approved as non-incentive circuits.
The following installation consisted of a constant-wattage tracer protected by a 120 VAC/20 amp circuit breaker. The installation was in a process operating area of an industrial facility.
A mechanic investigating a leak at the pump had removed the thermal insulation to determine the leak source. In the inspection process, the mechanic physically moved the electrical tracer not noticing that a metal hose clamp had been improperly installed over the tracer damaging the tracer sheath. The resulting movement of the tracer caused a fault.
The arc energy was sufficient to ignite the flammable process liquid which leaked from the pump. The quick thinking and action of the mechanic to remove power to the heater circuit and extinguish the fire prevented a potentially serious fire in an electrical hazardous area.