Maximum size breaker for heat trace cable

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brantdavid

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What is the maximum size breaker that the NEC allows to feed heat trace cable that is constructed with #14 awg buss wire?

I would like to use a 30 amp 2 pole EPD breaker with #10 awg wire connected to the heat trace cables. I have 3 runs of heat trace cable - 100ft, 30ft & 25ft. Voltage is 208V. The cable will be on the roof of a building.

I would normally protect the wiring in accordance with it's ampacity.

Thank You.

Dave Brant
 
I think that you're looking at this wrong. Don't size the cable based on the #14 AWG bus wire. Heat trace cable is designed with a resistance of so many watts per linear foot. I usually see 2W to 5W per linear foot. Check with the cutsheet or manufacturer. The load is likely to be on for more than 3 hours in a row so you can only use 80% of the rated value of the circuit breaker.

Even with that, at 208V, I would probably put all 3 loads on a single 15A/2P breaker. But you need to find out what the actual resistance is of the heat trace cable.
 
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Maximum size breaker for heat trace cable

Bill, Thanks. The cable I have is 15W/ ft. The manufacturer is Chormalox type SRM/E. The cut sheet suggests using a 2 pole 30 amp breaker to feed up to 270 ft of this type of cable. This cable is the self-regulating type that has a start-up current of 2 to 3 time the steady state current.

The manufacturers table shows using up to a 50 amp breaker to feed this type of cable depending on the length.

I am treating the heat trace cable as if it were a branch circuit conductor, which may be incorrect.

Regards,

Dave Brant
 
I'm a little confused. I see heat tape as a purely resistive load with no peak start up current like you find with motors. The cut sheet for that product appears to draw 16W/ft at the lowest temp shown. I can see this as the start up load and then as the tape warms, the load is "dimmed" by the self-regulating controller.

I still think the 15A/2P is good (just barely). But you should follow any manufacturer guidelines.
 
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