20A on 20A CKT

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QES

QES

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California
can you load up a 20a ckt with a 20a load.
I know that you can only load the receptacle(20a) with 80%=16A.
But the question is, can you do it even if it is less then 3 hours( non continuous)?
 
Yes you can load the circuit to 20 amps and even though you and I as electricians have to follow 210.21 I don't think many end users would hesitate to load a receptacle to what ever.

I also wonder how many inspectors lurk outside homes waiting to catch somebody violating this article section. :D

Roger
 
I think you can load a 20 amp breaker to 21, or 22, or perhaps even a few more amps, without tripping it any time soon. The maximum load we are permitted to design into the circuit is 20 amps in some cases, and 16 amps in other cases.
 
These are more or less typical preformance. In ambient conditions of 40C, a standard inverse-time (thermal), molded case circuit breaker should carry rated current indefinitely. Up to about 1.15 of rated current a standard breaker may trip as quickly as 60 seconds but it may not trip at all. Neither the former nor latter is too likely but either is possible. Above 1.15 rated current it should trip in some definite time less than 1000 seconds and the ?envelope? narrows progressively as the current increases.
 
Bob,
Above 1.15 rated current it should trip in some definite time less than 1000 seconds and the “envelope” narrows progressively as the current increases.
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I thought that the UL breaker standard permitted up to 60 minutes at 135% of rated current before tripping.
Don
 
don_resqcapt19 said:
Bob,
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I thought that the UL breaker standard permitted up to 60 minutes at 135% of rated current before tripping.
Don
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That may be what the standard is Don but I did a service call last wmonth where the 15 amp breaker would tripped with 18 amps on it. How long it took to trip I can't say. I did turn everything on the circuit and it amped out at 18 amps.
 
It depends on the specific breaker's time-current curves. And remember that these curves have some width. At steady current the breaker will trip some time between the left edge of the curve and the right edge of the curve. The left edge of the curve stops at 100% of the rated ampacity but the right edge can be as high as 130% of rated ampacity. I can see how some breakers may carry the load at 110% for several hours.

I just looked at the 20A, Square-D, QO curve and the left edge approaches 100% around 300 seconds (5 minutes). The right edge of the curve is at about 125% from 300 seconds to well beyond 100,000 seconds (2.78 hours).
 
Dennis,
That may be what the standard is Don but I did a service call last wmonth where the 15 amp breaker would tripped with 18 amps on it. How long it took to trip I can't say. I did turn everything on the circuit and it amped out at 18 amps.
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I am not saying that the breaker is required to carry 135% for one hour, I am only saying that it will pass the requirements of the standard if it does.
Don
 
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