The use of a ground-fault equipment protection device would detected the fault current in the early stages and tripped the circuit when there is problem with the system. It provides evidence that ground-fault problems are not limited to self-limiting cables.

The following lesson learned indicated a mineral insulated tracer protected by a 120 Vac/30 amp circuit breaker. The circuit was installed on a storage tank adjacent to the process operating area of a refinery.

A routine check of the heating controls found that the circuit ammeter was reading zero and the branch circuit breaker was in the tripped position. The breaker was reset and re-energized only to trip again.

When the thermal insulation was removed, it was found that 25 feet of the Mineral Insulated cable had vaporized from the end-seal. At that point the fault current was sufficient to trip the branch circuit breaker. Although the tracer failure occurred at a time when there were no flammable gasses or vapors present, this incident was potentially very serious due to the highly flammable nature of the tanked material.