Blue Sea Breakers & Cold Weather


Advanced Member
Sep 30, 2022
I have two Blue Sea circuit breakers on the cable between my truck battery and the camper’s lithium battery. We’ve had three nights this past week where the ambient air temperature was within a degree or two of -40F. I wanted to start the truck and run the engine to charge the truck battery and move the truck to another location. I tried to manually trip the breaker in the engine compartment to prevent any current to the dcdc controller but the breaker was frozen open. Same result when I tried the breaker in the camper. It appears that there was no way to prevent current flow to the dcdc.

I’m not sure what the implications are if there is a short in the cable during extreme weather situations. Or at what temperature the breaker freezes up.

In the future I plan to trip the breaker in advance of extreme cold temps.

Has anyone else noticed this condition with the breakers?
Curious. Any moisture to be accounted for? Like, did you wash the truck/camper before it got cold? Even then, I'm surprised.

As for implications, The Lithium Battery's BMS should protect it from any incoming current on the DCDC.
Negative 40F (= -40C) is the lower limit of the circuit breaker’s operating range according to the Blue Sea specifications. Assuming it’s not full frozen water, it could be a grease that turns to wax that keeps the lever from being thrown. That may or may not interfere with its thermal or magnetic tripping mechanism. You might want to call Blue Sea and ask about it. Theoretically it should work normally right at the limit temperature they stated.
You might test it by placing activated disposable hand warmers in contact with your circuit breaker(s) for a while to see if they start working again. No flame, run for a few hours, heats up to 135F. Charge your batteries after they connect. Camp in a warmer clime. :)

I am in the process of installing lithium in my camper and we are having temps in the teens and twenties with highs below 32. ( yes it’s Texas!) My bats do not have low temp protection as I figured normally 95% of the time it would be fine. My plan is to just disconnect the line from the battery to the ACR. I did try it with my old AGM it seemed to be fine.
I did install a Victron Smart Battery Sense for shutting off solar charging at cold temps and that seemed to work as well.
Disposable handwarmers are an interesting idea PaulT.

It’s been dry here for the last few months. An inch or so of dry snow accompanied the cold front but couldn’t effect the CB in the engine compartment or camper.

Thanks for the info on the CB specs. I suspected that there was an operating temperature range and -40(f/c) that seems to confirm it.

I plan to manually trip both breakers in the future in advance of extreme temperatures, maybe even when temps are anticipated below zero. I’m always concerned, with good reason, about equipment failures in extreme cold. I’d like to make sure there is no current flowing on that cable during those times.

Thanks all for the feedback.
I looked up the specs on the 285 CB and they include the same minimum operating temperature of -40(c/f). Also called Blue Sea and talked to technical support. The tech support engineer confirmed Jon R’s hypothesis that some lubricate had probably hardened due to the cold which prevented the plastic disconnect from functioning properly. He said that the two metallic blades that function as the circuit breaker would continue to function at the minimum operating temperature. I’ll test the manual disconnect on the breakers when it warms up next week, tech support expected no issues.

BTW, Blue Sea tech support was 5 star.

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