Heat Trace End of Life

[George Stolz]

How often would you say you've seen heat trace fail at the end of its life showing overcurrent versus undercurrent (or an open)?

A friend and I are mulling over possible solutions for an embedded heat trace cable that is kicking the breaker. The hope is that all is not lost and that the cable can be salvaged, and that there is some aspect of the problem that we are not seeing.

This is 277v heat trace that at some point in the past few years has been set to activate whenever the moisture sensor is triggered, regardless of outside temperature. To add insult to injury, GFPE was not functional during this period. My thought is that even though generally heat trace is self-regulating despite the settings at the controller, being energized during any summer rain has broken down the insulation of the tape and it is not salvageable.

The run does not megger, it's resistance to the circuit EGC is in the 100 ohm range.

As a follow-up question, I have been forced to ask myself what GFPE is supposed to accomplish in this scenario (since the knee-jerk reaction is to point a finger at the lack thereof). Suppose it were enabled when problems first arose, is the thought that it would deenergize the cable when things were just slightly askew in the hope that a single point could be repaired, or is it simply for protection against possible ignition due to failing cable grounding itself out as it went bad?

 

[George Stolz]

Oh - one other thing that is giving us pause is that there are other runs on this MWBC, introducing the possibility that somehow a neutral opened somewhere and somehow we are getting a higher voltage on the cable in question. I don't know of a point where the neutral could be opened and increase the current flow, every scenario I can think of reduces it. The run I am concerned about is naturally the longest of the set.

 

[StarCat]

Inspection points

Inspection points

Often times heat cable is poorly installed. The termination at the far end is a major offender for ground faults to metal pipe. The old school way is to terminate that end with double heat shrink and to use a thermostat on the pipe to shut the circuit off if it goes above a certain temp. Nowadays they have these gell filled end caps for large dollars.
I have seen so many installs where the cable is just left bare at the end.
The cable I have run can get water or whatever is in the pipe pretty hot if its static and not thermostatically controlled.
The thermostat on the pipe is a FAILSAFE control.
Sounds like you control system may have been given to some overheating over time.
So I check both ends of the run first. If the ends are good, and power is good then you are stuck with opening the entire run and replacing it.

 

[don_resqcapt19]

The GFP protection requirement is not to protect the heat trace, it is to prevent fires. Often the heat trace fault would not cause enough current to flow to trip a standard breaker, but it would produce enough heat to cause a fire. I think some of the original proposals for the heat trace GFP protection were based on a number of house trailer fires that originated in the heat trace below the trailer.

How old is the heat trace? I think that expected life is 12 to 15 years for most trace other than than the MI type.