Thatguy

11-19-2008, 12:42 PM

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

Thanks.

:confused:

Thanks.

:confused:

View Full Version : a trip curve for a plain-vanilla resi

Thatguy

11-19-2008, 12:42 PM

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

Thanks.

:confused:

Thanks.

:confused:

jwelectric

11-19-2008, 12:48 PM

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

Thanks.

:confused:

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.

Thanks.

:confused:

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.

Thatguy

11-19-2008, 02:03 PM

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.

:)

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.

:)