Self Regulating Heat Tracing Cable

Ask a supplier:Heat Tracing Products / Industrial Heating CablesHeat Tracing

"Self-regulating" might be a clue here.

...for the purposes of its being lower than the autoignition temperature of the flammable substance in the <...hazardous area...>.

The heat tapes I have worked with that had temperature controls had the sensing device at one end. If part of the tape is under insulation and another part not, or the tape was allowed to touch itself or worse yet, cross over. It was sure to develop a hot spot and burn out.

This problem is made worse by the heat tracing expanding when energized so if it had been installed absolutely tight when cold, it will stretch out when warm and that slack can allow the tape to slide and touch or cross over if it is wound around the pipe or vessel.

By definition, heat tracing tape will cover at least some distance, often a considerable distance, since hot spots can develop anywhere along the trace, are you going to put in thermostats every few feet or few inches?

I suggest that you carefully describe your desired installation with your heat tracing materials vendor, listen closely to their suggestions and follow their guidelines for use of their products in your application.

TT3

Self-regulating heat tape can parallel or cross over itself without developing hot spots.

My memory was of a heat tape back 15 to 20 years ago, that was self regulating. It was based on a positive temperature coefficient resistance of some sort of solid state material. You could cut it off of a roll (any length), and crimp on the power connection. The installer would also crimp on an insulating end. It had a real problem that the unsealed wires at either end, if it got wet, the cable started shorting and arching, and a fire of the plastic insulation occurred. As it consumed it self, it burned like fireworks fuses. It was used extensively in mobile homes here in the Midwest as the underside of these trailers was not heated. At any rate there were many unexplained fires, as these structures would normally 100% loss by un-determinable cause of ignition source.

The person who can do this is the technical sales contact at the vendors of hazardous area self-limiting trace heating tape. Make the phone call.

After using such traces for a number of years and discovering some will get hot enough to burn polypropylene around them, although they claim to limit to 250 degrees, I finally found the temperature/wattage curves and even at 250 degrees F they have a significant wattage output. Apparently the "self limiting" is assuming an open air exposure on a roof at around 32 degrees ambient. Under those conditions, the wattage output would not be enough to heat any higher in temperature. We have driven a 250 degree "self limiting" to 305 degrees in tests in ambient temperatures of 75 degrees F, and poor air circulation.

If you need to limit to a lower temperature, yes, you need a thermostat. Why not just use the "non-limiting' type and a good temperature control unit? Precision Digital, Red Lion, and many others make very reliable relatively low cost temperature controllers that are quite programmable.

Many self regulated heat lines will draw power even when there is no demand. These are honeycombed networks of conduction wires that will draw 1 watt per foot with no demand and 5 watts per foot when the demand is peaked. The advantage of these contracting networks is that they will create more connections (cold contracts the honeycomb) only in the area needed and not throughout the full length of cable. If you do not need the heat cable in summer time just shut it off. Otherwise it is self regulating along its entire length and no external thermostat is required.

Electrical heat tracing cables are normally not allowed in hazardous locations. Unless there is something unique or special with the system you are asking about electrical wouldn't be allowed.

Steam tracing is normally used in hazardous locations. Copper or some other tubing is placed against the piping, vessel or other unit and steam fed through the tubing. Usually insulation is used to cover the unit and the steam tracing to make it more effective and efficient. Traps and thermal controls are also incorporated to regulate the temperature of the tracing.

I can't remember any installation in my numerous years (retired now) in a hazardous location where electric tracing was used (too risky and expensive)!

Also, heat tracing tapes can not be crossed over itself as others have stated. This is the first thing to fail if done so. Electric Heat tracing 101.

Good Luck, Old Salt

Evidently you didn't take Electric Heat Tracing 201, which came along after self-regulating heat tapes were invented, and made part of 101 obsolete.

Following Electric Heat Tracing 101 kept us out of trouble if it was followed. Most electric heat tracing tapes including self-regulating explicitly state "do not cross". Also, I have seen numerous ones that were crossed and failed at the crossing point. Failures in a hazardous location tend to be extensive failures with collateral damages and frozen materials that must be thawed or cleaned up. Following the "do not cross" practice is much cheaper and safer than a hazardous area fix and clean up. It also does not expose personnel in the area to a potential accident.

Why take the risk?

Old Salt

Have been installing heat trace in hazardous rated areas, both CL I & II, for 25+ yrs. Never had an installation that wouldn't require a thermostat or controller of some sort. Is this for freeze or process protection? What type piping? Regardless, contact your local Raychem/Chemelex or Thermon rep. Most hazardous rated, self-regulated, tracing, start at 65 C. Redundant and or some sort of indication of thermostat failure may also be needed. Ran across an installation where process heat tracing was used for freeze protection on an eye wash station. Thermostat failed, eye wash became a geyser, during a routine safety check of the station's operation. The self-regulating tracing, was rated at over 160 C. Be careful, if you don't know, contact those who specialize in these installations. They will be more than glad to assist you.

It is a bit more complex than the ambient temperature that drives the thermostat.

Self Regulating Heaters are safe for usage in hazardous areas: check the approval for the zone classification to know whether it would fit your zone. (contact the Authorothy having Jurisdiction to take decisions)

Cables exist with unconditional rating T2 till T6: just the cable will never go over the classification borders, overpowered, on a spool, nicely insulated.

So to answer the original question: NO

For energy consumption it is alway's wise to use line sensing: keep the pipe exactly at the temperature you require and not more.

A cut-off heater does not exist, they all have a negative temperature-power relation that will reduce the power as the heater gets hotter.