Circuit breaker tripping point

[J.L. Swift]

How long would a 15amp breaker hold at 24.55 amps ? There is a post on the electricians only group of an electrician holding an amp clamp on a 14 gauge wire to a 15amp amp breaker for at least a minute and it is not tripping. Is the breaker bad ?

 

[kwired]

How long would a 15amp breaker hold at 24.55 amps ? There is a post on the electricians only group of an electrician holding an amp clamp on a 14 gauge wire to a 15amp amp breaker for at least a minute and it is not tripping. Is the breaker bad ?

Don't know what listing standards are, but I think most general purpose thermal magnetic breakers would likely hold at least one minute at this percentage of overload, presuming "cold start" as in they weren't already preheated by other loading or loading periods.

Might even hold at least 15 or even 30 minutes at that current level in some cases and very well could still be within listing standards. If the load would happen to vary that can change things, if 24.55 is the high peak it could be even longer, if it is the low peak it will likely trip even sooner.

 

[jim dungar]

How long would a 15amp breaker hold at 24.55 amps ? There is a post on the electricians only group of an electrician holding an amp clamp on a 14 gauge wire to a 15amp amp breaker for at least a minute and it is not tripping. Is the breaker bad ?

I would not find it unusual to see a breaker carry 200% load for almost a minute. This would be especially true if the ambient temperature around the breaker was less than 80F.

Need to know exact breaker catalog number and breaker ambient temperature to give an exact time. A 15A BQ would hold it for almost 30sec at 104F.

 

[ptonsparky]

I've seen a GE that was repeatedly reset on a fault eventually hold at 60 amps. I didn't wait for it though.

 

[dkidd]

This Square D TCC indicates that it could take from 60 to 300 seconds.

 

[don_resqcapt19]

And that trip curve is based on the temperature of the breaker being 40°C. If the actual breaker temperature is less than that, the curve shifts to the right, and will hold that amount of current even longer.

 

[dkidd]

And that trip curve is based on the temperature of the breaker being 40°C. If the actual breaker temperature is less than that, the curve shifts to the right, and will hold that amount of current even longer.

Yes, but it isn't much of a shift.

 

[powerpete69]

Right. Depends on the breaker curve of that specific breaker. Wide range.

 

[dkidd]

And that trip curve is based on the temperature of the breaker being 40°C. If the actual breaker temperature is less than that, the curve shifts to the right, and will hold that amount of current even longer.

I think you meant left.

 

[jim dungar]

I think you meant left.

I don't know what those temperature ratings are for, on the graph that you posted.

The TCC, that Don posted, is for a Square D breaker. According to their guide for determining current carrying capacity in special applications:
Ambient temperatures 25 to 40C - no derating necessary
Ambient temperature -10 to 24C - breakers will carry more continuous current (for a QO115, this would be about 19A at 0C)
Ambient temperature 41 to 60C - breakers will carry less continuous current and nuisance tripping is likely.
However they do not provide any guidance on how to modify, or redraw, their TCC.