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Old 05-29-2012, 11:40 AM   #1
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Default Brown out overloads

True or untrue- Circuit breakers are more likely to trip during heavy load brownouts.

Or is it just the heat ?

I tend to see many applainces, pool filters , ACs, refrigeration tripping OCPDs on heavy use days when POCOs have a lower voltage in the system.

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Old 05-29-2012, 11:42 AM   #2
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I have always seen it as a heat issue.. same as when the buss is going bad..

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Old 05-29-2012, 01:25 PM   #3
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Well some breakers have UV devices so they will trip on a UV condition to prevent an overcurrent condition.

If voltage drops, the loads will draw more current and OCPD trips are likely to occur.
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Old 05-29-2012, 03:30 PM   #4
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Quote:
Originally Posted by Shockdoc View Post
True or untrue- Circuit breakers are more likely to trip during heavy load brownouts.

Or is it just the heat ?

I tend to see many applainces, pool filters , ACs, refrigeration tripping OCPDs on heavy use days when POCOs have a lower voltage in the system.
If the load has an AC motor in it, AND the load on the motor remains the same when the voltage drops, the motor torque drops by the SQUARE of the voltage change. So for example lets say the "brown out" is a 20% votlage drop, i.e. 240V becomes 192V. The motor torque applied to the load drops to .8 x .8 = 64% of what it was designed for, but since the frequency stays the same, the HP then drops to 64% of rated (HP is an expression of torque and speed). If the motor was running at 80% load and the motor HP then drops to 64% of what it was, you are in overload. The motor will slip more which means it will draw more current to make up for the loss of torque. Then it becomes a race as to what is going to trip faster, the thermal protection device for the motor or the thermal trips in the breaker or other OCPD. Ideally you want the protective device closest to the problem to trip first, but in residential and light commercial applications, a coordination study is rarely done to ensure that and the CB trips. It has to.
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Old 05-29-2012, 08:12 PM   #5
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Jraef that sounded just like an Explanation given by an Emerson drive rep. It was waaaay over my head then ....
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Old 05-29-2012, 09:14 PM   #6
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Jraef that sounded just like an Explanation given by an Emerson drive rep. It was waaaay over my head then ....
Is it still?
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Old 05-29-2012, 09:42 PM   #7
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Quote:
Originally Posted by JRaef
Is it still?
No. I am learning. Specifically he mentioned the race as to what trips first.

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