# Minimum storage and operating temperatures for plc modules



## sparky970 (Mar 19, 2008)

If you have spare chassis and power supply put them in a rack and keep energized.


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## oliquir (Jan 13, 2011)

i have plc outdoor here (can go down to -35C) with no heat in panels and they work for over 10 years now, some of them are shut down for winter and restarted for summer with no problems.most of the parts can be at -40C they are just not tested at this temp since it is not a very common temperature


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## JRaef (Mar 23, 2009)

Electrolytic capacitors can freeze and blow up when re-energized (but few PLC cards will use electrolytic caps any more), and PC Board traces can shrink and crack. But still, you can only do what you can do.

I would just take precautions, via a reverse-acting thermostat, against applying power until the enclosure air temperature increases after a power loss. What I do is use what is called a "freeze-stat" that you can get from refrigeration suppliers, which CLOSES on temperature rise. The intended use is to bring on a compressor when the freezer gets too warm, but you use it to close a Line Contactor that feeds power to everything else in the panel ONLY after the air inside gets to some acceptable level. If there are larger devices such as VFDs or big power supplies that might have electrolytic caps inside, that needs to be 40F (4C) but for just PLCs and such, it could be their lowest rated OPERATING temperature. So from your incoming terminals, you go to the strip heater and the line side of the contactor, then everything else comes off of the load side of that contactor, and the contactor coil goes through the freeze-stat.


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## xpertpc (Oct 11, 2012)

I second the motion on using a freeze-stat to bring the enclosure up to temp before re-energizing the electronics for another reason - condensation.

Most PLC and electronics always specify "Non-Condensing" and with extreme temperature differences you will get condensation.

I witnessed this first hand with a 12,000 volt bank of switch gear one January night at -10F, we lost plant power for about 10 minutes and went outside to check the switch gear which was not tripped.

Once the short at the substation cleared the circuit re-closed, it sounded like someone threw a bunch of ball bearings inside the 6 bank enclosure with a giant spark and a hole the size of a baseball coming out of one side.

Once the gear was locked out and opened we saw that the entire inside of all 6 bays were wet with condensation. 

That may be an extreme example but it is also why I always let electronics that have sat outside to warm up to room temperature before powering up.


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## KennyW (Aug 31, 2013)

Thanks guys these thoughts all resonate with me. I think a freeze stat is probably a good policy and easy to add since it's just a passive device. I think I will do that and just see how it goes. 

The other issue is even if the lifespan of the parts drops from 20 years to 2, they're easy to change and fairly cheap. They have some special features and solve some other problems that lower temp rating io won't do, so I think it'll work out. 

Cheers guys!


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