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[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.

[mike henrich]

I'm the guy who sent the email to Mike.    First off,   thank you Mike and thanks everyone for the quick responses.

I wanted to take my IF thermometer with but forgot.  So I may run the AC at home tomorrow and see what the temp is and also take an amp reading.  I can tell you that I cannot hold my finger on the breaker for long.    I can't believe the fan cooled it so much,  but it did.

The answers on here settled my mind on what I was thinking was an OK fix.

Thanks again.  I'll post the readings when I get them.

[Tim McCulloch]

I'm the guy who sent the email to Mike.    First off,   thank you Mike and thanks everyone for the quick responses.

I wanted to take my IF thermometer with but forgot.  So I may run the AC at home tomorrow and see what the temp is and also take an amp reading.  I can tell you that I cannot hold my finger on the breaker for long.    I can't believe the fan cooled it so much,  but it did.

The answers on here settled my mind on what I was thinking was an OK fix.

Thanks again.  I'll post the readings when I get them.

Thermal imaging is your friend. 

I've been reading the IRV2.com forums for the last few days, down the rabbit hole after finding (mostly) what I was looking for.  Aside from being in a part of the coach with little air circulation I'd suspect a loose or corroded connection (likely at the breaker).  Since you've replaced 1 or more of them and as you're an electrician I'd expect you've already checked for that...

Something to check for that might have escaped first notice:  what size is the load wiring?  One RV owner found #14 wire on the *supply side* of his coach so I suspect anything is possible.

My final thought is "what changed"?  Unless this has been a problem since you bought the unit in 2009, something had to happen.  The question is what.

[Mike Sokol]

In case any of you own RVs and are curious about I write for that industry, here's what I've been up to lately: www.rvelectricity.com

[Jonathan Johnson]

So, can we assume that a power distro on a sound system that's sitting out in the sun on a hot day could be subject to thermal tripping caused by environmental heating?

And it may not be a bad thing. After all, the same sun that heats up the breakers also heats up the wires; when the wires are hot, the current carrying capacity may be reduced since it may limit how much additional heating may be allowed when caused by current.

In the case where the wiring is environmentally heated the same as the breakers (unlike the RV, where only the breaker panel is being heated by the inverter), could cooling the breakers without also cooling the wiring result in a hazardous condition?

(Mike, I'm trying to bring this back around to the forum focus, since it definitely could be an issue for sound providers.)

[Mike Sokol]

So, can we assume that a power distro on a sound system that's sitting out in the sun on a hot day could be subject to thermal tripping caused by environmental heating?

And it may not be a bad thing. After all, the same sun that heats up the breakers also heats up the wires; when the wires are hot, the current carrying capacity may be reduced since it may limit how much additional heating may be allowed when caused by current.

In the case where the wiring is environmentally heated the same as the breakers (unlike the RV, where only the breaker panel is being heated by the inverter), could cooling the breakers without also cooling the wiring result in a hazardous condition?

(Mike, I'm trying to bring this back around to the forum focus, since it definitely could be an issue for sound providers.)

Yes, and that's of the reasons I posted this here in the first place. Many times I've done gigs out in the sun where the console and everything else gets too hot to touch. Of course, I try my best to tent everything properly, but sometimes it's just not possible.

And I've had power distros and temporary circuit breaker panels out in the sun as well. I did have one outside gig many moons ago where the service panel was sitting in the direct sun and tripped a few breakers we couldn't imagine were overloaded, and one of the guys put a box fan on it which solved the tripping problem, or so we believed. This was probably 30 years ago so I wasn't paying as much attention to power distribution as I do now.

And certainly I've had 2/0 and 4/0 cables laying in the direct sun for days on end. But lucky for us (maybe) when the sun was shining we didn't use stage lighting and visa versa.

Oh, last year a preacher was on an outside stage without a roof and his iPad overheated in the sun, cutting his sermon short by at least 30 minutes. Act of God? Maybe.... But I sure was happy to move the service along and get out of there.

Any other experiences with tripping circuit breakers that were sitting in the sun or installed in an unventilated room?

[Tim Weaver]

fwiw, in my last touring gig we had a 96 Prevost that had the circuit breaker panel in the back of the pantry. The Inverter was somewhere in that same set of cabinets. It would definitely get hot and trip during the summer. We had to leave the pantry door open during the day to keep stuff working.

Any time of the year, the heat buildup inside the pantry was pretty big. It would be 90-100 degrees in there when you opened the door.

[ProSoundWeb Community]