Breakers warming quickly

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matt123

Member
So we did a new solar installation and each inverter is putting out 32 amps on #8thhn on a 2 pole 40 amp breaker. There are six of them in the system. After running for about a half hour each of the breakers were recording a temperature of 107-109 degrees. The breakers are all staggered and spread out through the 200 amp breaker panel. Getting too warm too quick? or too warm in general? Thanks for your input.
 

kwired

Electron manager
Location
NE Nebraska
Reason you seldom notice any heating of breakers in a house is not much ever runs continuously. Sometimes you may notice heating of an air conditioner breaker or a heating unit breakers during extreme heat/cold conditions when those items do end up running nearly continuously.

Go to commercial/industrial installations and you will notice heating of continuous loaded breakers more so than in a house.

Your PV system is also putting same load level out for long periods of time and will heat those breakers up some. But as mentioned, they are rated at 40C, which isn't extremely hot, but is pretty warm for people who have a normal body temp of slightly less.
 

beanland

Senior Member
Location
Vancouver, WA
40C

40C

40C is 104F, as hot as a spa, but that is the breaker ambient.

Wire rated for 75C would be at 167F, hot enough to cause skin burn if touched for more than a few seconds, but still within its design rating.

I was around a power transformer operating at 90C, well within its design, but you could not get close because it was like a furnace radiating heat.

The point is that our senses are not a good indicator of what is safe for electrical equipment.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
40C is 104F, as hot as a spa, but that is the breaker ambient.

Wire rated for 75C would be at 167F, hot enough to cause skin burn if touched for more than a few seconds, but still within its design rating.

I was around a power transformer operating at 90C, well within its design, but you could not get close because it was like a furnace radiating heat.

The point is that our senses are not a good indicator of what is safe for electrical equipment.
Well, I believe our sense of smell can be a pretty good indicator. :D
 

matt123

Member
Sense of sight too, if it glows. And sense of hearing if it arcs. :angel:

Went out today and checked it out and the breakers are reading 135 degrees. Seems hot so I called square d and talked to one of their engineers and he said that breaker can go up to 185. Anyone have any inverters running 32 amps at that temp? Seems hot or am I just over thinking it?
 
If you're really curious, do a fall-of-potential test (measure the voltage drop across the breaker)- usually shouldn't be more than a couple of millivolts. Multiply that by the current and you have the power being dissipated by the breaker.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
It does seem hot, but don't jump to conclusions about the breakers themselves. That heat could easily be getting transferred along the bus or conductors from another hot spot, such as the lugs for the panel feeder. To be thorough, shut it all down and check all the nearby terminations. Bring torque tools.

On the other hand, if anything is going to put a compliant installation to the test, solar inverters in the summer will. And that temperature is not something the equipment isn't designed for.
 

kwired

Electron manager
Location
NE Nebraska
So we did a new solar installation and each inverter is putting out 32 amps on #8thhn on a 2 pole 40 amp breaker. There are six of them in the system. After running for about a half hour each of the breakers were recording a temperature of 107-109 degrees. The breakers are all staggered and spread out through the 200 amp breaker panel. Getting too warm too quick? or too warm in general? Thanks for your input.
From what you mentioned I am seeing 6 breakers with a relatively constant load of 32 amps - which would be 192 amps, all connecting to a 200 amp panel. Don't know my codes for PV systems all that well, but seems you may have a little too much PV connected to this panel just with what I mentioned here. I'd expect some heat from that kind of continuous load regardless of whether it was input from PV or just conventional loading of same amps.
 

matt123

Member
From what you mentioned I am seeing 6 breakers with a relatively constant load of 32 amps - which would be 192 amps, all connecting to a 200 amp panel. Don't know my codes for PV systems all that well, but seems you may have a little too much PV connected to this panel just with what I mentioned here. I'd expect some heat from that kind of continuous load regardless of whether it was input from PV or just conventional loading of same amps.

The weird thing is that the bus is not heating up at all. All connections were checked and only hot spot is the breaker casing.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
From what you mentioned I am seeing 6 breakers with a relatively constant load of 32 amps - which would be 192 amps, all connecting to a 200 amp panel.

He's got 32A per breaker, but each one is only connected to two of the buses. It's a group of single phase inverters connected phase to phase to a three phase service.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
The weird thing is that the bus is not heating up at all. All connections were checked and only hot spot is the breaker casing.
Sounds like it's coming from the breaker's internals, then, so it must be called "normal" for its use.
 

kwired

Electron manager
Location
NE Nebraska
Main lug 3 phase panel. Inverters are single phase but the 6 breakers balance out the phases.
Ok that reduces the current in the 200 amp panel - my comment of 192 amps was for a single phase source.

Don't know enough about PV systems, can you tie such units to a three phase system or do you need an inverter(s) with three phase output?
 
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