a trip curve for a plain-vanilla resi

Discussion in 'Electrical Forum discussion & Blog' started by Thatguy, Nov 19, 2008.

  1. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    15A breaker to be used with #14 AWG copper; anyone have a link?

    Thanks.
    :confused:
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina

    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. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    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.
    :)
    Last edited: Nov 19, 2008
Similar Threads: trip curve
Forum Title Date
Electrical Forum discussion & Blog Circuit Breaker trips same time every day Aug 25, 2013
Electrical Forum discussion & Blog Breaker tripping Jul 12, 2013
Electrical Forum discussion & Blog Trying to debug GFCI tripping May 21, 2013
Electrical Forum discussion & Blog Loud boom and tripped breakers May 28, 2012
Electrical Forum discussion & Blog triplex breaker 20/20/20 single 2 pole 20a, dual COMMON TRIP 1 pole 20a? Feb 27, 2012

Share This Page