Heat Tracing Cables - Thermostats

[Charz]

I read a Heat Tracing specification that reads, "The use of thermostats for controlling oversized self regulating circuits shall be avoided." Also the same spec reads "Each circuit shall be furnished with an “in-line thermostat”, to switch the tape off before the design limits are reached".

My questions are,
1. Why does self regulating cables require thermostats?; As it cannot get hot enough to overheat and cause damage to itself.
2. What does “in-line thermostat”, to switch the tape off mean?

 

[ptonsparky]

IMO. They are telling you to size the equipment properly. Don't put in 25 watt per foot when 5 is the proper size.

 

[don_resqcapt19]

1) Even with the self regulating heat trace you use a thermostat to avoid wasting energy. For example if the heat trace is for freeze protection the stat is typically set to keep the trace off until the the temperature is below 36°F or so. This is often an ambient, and not line sensing thermostat.
However is it also saying what post 2 says.
2) Not really sure what they mean by "in-line thermostat", but expect they are talking about a line sensing thermostat where the sensing element is attached to the pipe being traced under the insulation. This saves even more energy as the trace does not turn on until the pipe itself reaches the temperature that the stat is set to turn the trace on.