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Fan on a circuit breaker panel?
Mike Sokol:
I just received this email from one of my RVelectricity readers. I suspect he's getting a lot of heat buildup from the inverter which is causing the breakers to trip. In RVs like this the manufacturers usually cram the inverter and circuit breaker panel into a little box that certainly would trap heat. Have any of you seen any studies on the effects of ambient air temperature on circuit breaker trip thresholds?
Hi Mike,
I'm an electrician and enjoy reading your articles on RV Travel. I have a dilemma with my own RV I wanted to throw at ya.
I have a 2005 Sunseeker Class C. We bought it used in 2009. The electric panel, 12 volt fuse box, and inverter are mounted near the floor, next to the bed, in an area with absolutely no air movement.
Ever since we owned it, the fan on the inverter would cycle on and off very often.
We have trouble with the AC breaker tripping. I know about the lower voltage, etc. But, the breakers get extremely hot. I've replaced the breakers and checked all connections, and even put a new 30 amp cord end on. I also cleaned the coils on the AC.
I decided to try something this past weekend seeing as the temps were in the mid to upper 90's. I have a 12 volt fan that I plugged in and aimed towards the breaker area. Not only did the breakers stay cool, but nothing tripped and the inverter fan was not cycling on and off. The voltage on my kill-a-watt meter was down to 110 at 1 point, plugged into a different circuit.
My question is, is this safe to do? Or am I not allowing the breaker to do it's job by keeping it cool? That's the technical side of the components I don't know much about. I see fans on bigger panels often.
Thank you,
Mike Henrich
Art Welter:
Seems smaller breakers derate with heat more than larger ones.
According to the chart here:
http://bdbreakers.com/breakertypes.php
a 15 amp (Siemens) breaker will trip at 17 amps at 77F, 13 amps at 122F, and only 11 amps at 140 degrees.
The inverter I use in my trailer probably exceeds 140 degrees before the cooling fan comes on.
Using a fan to lower the heat would (or could) keep the breakers operating at their nominal rating. It may also eliminate the annoying cycling of the inverter fan..
Stephen Swaffer:
Since most breakers used in these situations are "thermal-magnetic" heat will definitely affect them. I've diagnosed breakers tripping at a low current becasue the connection was loose and creating extra heat.
Best thing to do is ask the manufacturer:
https://www.schneider-electric.com/resources/sites/SCHNEIDER_ELECTRIC/content/live/FAQS/278000/FA278588/en_US/Determining%20Current%20Carrying%20Capacity%20in%20Special%20Applications%200100DB0101.pdf
Erik Jerde:
It would be useful to know how hot they are getting. A non-contact IR thermometer is great for things like this.
Tim McCulloch:
I have nothing to add accept that in most Class C & B coaches the converter/charger/inverter is usually under the rear bed, adjacent to the galley. Also under the bed tends to be the fresh water tank and some storage. Ventilating the under-bed area with a small 12v fan and installing a grate couldn't hurt.
To me it's amazing how poorly thought out some RV systems are. I've been reading horror stories about workmanship, materials, and general lack of QC for the last 3 days. Fortunately I'm not currently experiencing any "surprise" issues as my 2006 Four Winds 23A has been shaken down by previous owners. Now I deal with wear & tear stuff - awning and chassis mechanical stuff mostly.
Price and class don't seem to be a significant factor, at least for some brands - spending $80k or $400k - all models have similar deficiencies that are left to the dealer (good luck) or purchaser to remedy. RV manufacturers haven't learned from the US auto industry of 30 years ago.
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