Transformer and Thermostat Operation at - 40Deg C 1

[nightfox1925]

I have a heat trace controller used for heating insulated busbars for an overhead crane installed outdoors.

The minimum ambient temperature during winter time here is -40 Deg C.

The controller box has a Thermostat controller rated for

-34 to +66 Deg. C (Operating)
-40 to 85 Deg C (Shipping)

A 250VA dry type CPT and Square D magnetic contactor are also installed in the same control box (NEMA 4X).

I am intending to install this heater control box outdoors near the busbars to be heated. The control box components will be subjected to -40 deg C.

I would like to get some guidance if this will be acceptable. Furthermore, I am not sure on the "shipping" temp. ranges for the thermostat mean.

I will appreciate any comments. Thank you.

 

[dpc]

It means the device will survive in the box at -40 deg C, but is not meant to be operated at -40 deg C.

 

[waross]

An anecdote that may or may not be important.
We had a temperature alarm that had a limit of about 32F. We wanted to use it outdoors in a colder ambient. We did some testing and found out that the operating limit was the limit of the thermocouple reference junction correction. As the temperature went lower, the alarm point went lower by the same amount. That is at -10F the device alarmed 10F below the set point. We decided that if we were getting close to alarm conditions when the ambient was that low, we didn't mind the alarm coming in a little early. We used the device as is and never had a problem.
We had a similar problem with hoar frost forming on overhead crane bus bars. We installed a power correction capacitor at each end of the bus bars (center fed) and the current to the capacitors was just enough to keep the hoar frost off the bars.

Bill
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"Why not the best?"
Jimmy Carter