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# Thread: a trip curve for a plain-vanilla resi

1. ## a trip curve for a plain-vanilla resi

15A breaker to be used with #14 AWG copper; anyone have a link?

Thanks.

2. Originally Posted by Thatguy
15A breaker to be used with #14 AWG copper; anyone have a link?

Thanks.

Just what are you looking for?

A good rule of thumb concerning the trip curve of a breaker is six times the rated current.

Your 15 amp breaker will carry 90 amps for 12 cycles without tripping.

3. Originally Posted by jwelectric
Just what are you looking for?

Reverse engineering the NEC.

A good rule of thumb concerning the trip curve of a breaker is six times the rated current.

Your 15 amp breaker will carry 90 amps for 12 cycles without tripping.
Good. That's exactly what I'm looking for.

So the I-squared-T rating for this breaker is 8100 x 12/60 = 1620 amps-squared-seconds.

For one-half cycle at 60 Hz this should trip at 440A.
With a dead short at the end of 1/4 ohm worth of Romex the rms current for this half cycle would be 120/(1/4) = 480A.
Close enough.

If #14 AWG copper fuses at ~170A (in one second?) then its rating is about 30,000 (A^2)-sec. So the breaker interrupts the current before the wire gets anywhere near the melting point, maybe when the wire reaches 90°C or so. . .?

Thanks.

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