We buy heat trace cable.

Two families of heat trace

Self-regulating cable has a conductive polymer core that changes resistance with temperature, drawing more power when cold and less as it warms. It can be cut to length in the field and spliced with the correct kit, which is why it turns up in odd lengths rather than on full reels. Most plant trace in this region is that type. It also means a coil of trace is never quite the length the label claims.

Mineral-insulated cable works on a different principle: a conductor inside magnesium oxide powder inside a metal sheath, built to run hot and last. MI trace is ordered to specific lengths with factory terminations, so a cut length with its termination removed is a different proposition from a reel, and it is graded that way. The sheath is the tell: MI trace looks like small tubing, not like cable.

• Self-regulating polymer trace in cut lengths
• Mineral-insulated trace with a metal sheath
• Cold lead and power connection kits
• Trace on original reels, still banded
• Thermostats and control components from the same store

Why it is reviewed separately

Cable that carries power to a load is judged on conductor and jacket. Heat trace is judged on whether it still heats. The conductive core can be damaged by a pinch, a kink or a bend radius that was ignored during installation, and none of that shows on the outside of the jacket. The readings are the only honest test. A length that reads open at one end is finished, whatever the jacket looks like.

That is why a heat trace lot is not valued on weight. Continuity and resistance readings at the ends tell you whether a length is alive, and the numbers are compared against the wattage printed on the jacket. Where no reading can be taken, the material is treated as uncertain, and uncertain is not the same as finished. Record the reading and the temperature at which it was taken, because both change the number.

Cut lengths and the splice question

Most heat trace arrives in cut lengths, because that is how it is installed. A length cut for a forty foot run is a forty foot length, and there is no way to make it longer again. Reuse is limited to a run of similar size, which narrows the field of buyers without emptying it. The leftover is a fitting problem rather than a cable problem, and the next similar run solves it.

Splices are permitted on self-regulating trace when the correct kit is used, and a properly spliced length is still serviceable. On MI cable the termination is factory work and a field splice is another matter entirely. Both are inspected rather than assumed to be fine, and the cold lead is checked with them. Ask who made the splice and whether the kit came with it.

Keep the end kits, junction boxes and connection components with the cable. Loose trace without its terminations is harder to place.

Freeze events and plant stores

A hard freeze on the Gulf Coast produces a season of heat trace work: new installations, repairs after failures, and material bought in a hurry that was never used. The surplus surfaces in stores the following summer, still in its cartons, behind the items that move. Stores staff usually know exactly which shelf it is on. It was bought for a freeze that did not arrive, which is why it is still boxed.

Send the trace type, the voltage, the wattage per foot if it is printed, the length and whether the ends are terminated. Where a plant store holds a mixture, list it by type and length rather than by part number, which is often the least useful line on the label and the one most often read out over the phone. A store with forty part numbers and no lengths is harder to review than one with four types.

• Trace type and voltage
• Wattage per foot at the reference temperature
• Length, and whether it is continuous
• Terminated ends or bare
• Storage conditions since removal