210.20(A) maximum load is it 80%?

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tom baker

tom baker

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Was asked the following question today and like to pass these on to the forum
210.20(A) states the maximum load on a overcurrent device is 125% of the continuous loads plus 100% of the non continuous loads

Commonly its stated that you can never load a branch circuit to more than 80% of the overcurrent device rating (80% is the inverse of 125%)

Does this mean for non continuous loads the overcurrent device can be loaded to 100%?
 
doesn't a standard breaker only have a 80% duty rating? ..You could get a 100% duty breaker but they're expensive

I thought that was why you only loaded at 80%..
 
SiddMartin said:
doesn't a standard breaker only have a 80% duty rating? ..You could get a 100% duty breaker but they're expensive

I thought that was why you only loaded at 80%..
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Code wise you can load a standard breaker 100% up to 3 hours at a time.

A 100% breaker can be loaded to 100% forever.
 
BackInTheHabit said:
Just wondering your opinion Roger.

What about 210.23(A)(1)

I realize this refers to cord and plug connected equipment, and there probably wouldn't be a continuos load, but could they be referring to the 80% mentioned here?
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IMO this section is a waste of ink, how is it going to be enforced?

Does the CMP think the end user is going to reference the NEC when they plug something in?

Roger
 
roger said:
Does the CMP think the end user is going to reference the NEC when they plug something in?
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Roger, once again you've forgotten that the purpose of the NEC is to cover all the "what if's" that we encounter every day.
 
tom baker said:
...plus 100% of the non continuous loads

Commonly its stated that you can never load a branch circuit to more than 80% of the overcurrent device rating (80% is the inverse of 125%)

Does this mean for non continuous loads the overcurrent device can be loaded to 100%?
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Yep, that's the way I understand it as well, literally.

I was one of those who installed for years with this 80% thought until I came across a 2400W microwave that was tripping a 20A breaker. I told the guy that owned it that it's a defect "throw it away". He would not part from it so I replaced the 20A breaker and the 12's with 10's, I don't even know if the conductors mattered but I did it anyway. Well that's when I dug into the NEC to qualify this 2400W load and found it could 210-19.
 
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If I remember this right the NEC used 80% for branch circuits, overcurrent devices, continuous loads and such. Maybe it was the 90 code that it change and started using 125%? Does anyone remember when this took place? I had this talk many times with some in house guys and they still use the term 80% for everything.
 
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