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Thread: Breakers warming quickly

  1. #1
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    Breakers warming quickly

    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.

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    Quote Originally Posted by matt123 View Post
    Getting too warm too quick? or too warm in general? Thanks for your input.

    That temperature is not warm for a breaker. Molded case breaker are tested at a 40C (104F) ambient.
    Just because you can, doesn't mean you should.

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    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.
    I live for today, I'm just a day behind.

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    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.
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    Quote Originally Posted by beanland View Post
    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.

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    Quote Originally Posted by ggunn View Post
    Well, I believe our sense of smell can be a pretty good indicator.
    Sense of sight too, if it glows. And sense of hearing if it arcs.

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    Quote Originally Posted by GoldDigger View Post
    Sense of sight too, if it glows. And sense of hearing if it arcs.
    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?

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    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.

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    Remember both the bus and output connections need to be low-resistance.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
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    Richmond, VA

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    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.

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