on a 150 foot run, the equivalent circuit ac resistance for 20 amps at 120 v is .6 with 12 ga and .36 with 10 ga. I am not able to calculate how much this would affect the opening time of a circuit breaker, and would like to know if any of you EE geniuses want to do the math.
10s and 12s
- Thread starter dezwitinc
- Start date
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- Location
- Illinois
- Occupation
- retired electrician
The trip curve for one major brand of breaker show a trip time from instant to 0.5 seconds for the #12 (200A) and instant to 1 cycle for the #10 (333A).
Don
ptonsparky
Tom
- Occupation
- EC - retired
I do know from personal experience that a long circuit with minimum sized feeders and EG does not necessarily open the fuses quickly enough.
A bolted fault at the far end of the circuit dropped the voltage low enough that the phase monitor, located about mid point, would open the control circuit before the fuses blew. I watched it cycle and had enough time between trips to connect meters. The total impedance of the circuit was to great.
I designed it & I installed it so I had no one else to blame.
Learning experience. Go ahead and borrow it.
A bolted fault at the far end of the circuit dropped the voltage low enough that the phase monitor, located about mid point, would open the control circuit before the fuses blew. I watched it cycle and had enough time between trips to connect meters. The total impedance of the circuit was to great.
I designed it & I installed it so I had no one else to blame.
Learning experience. Go ahead and borrow it.
It sounds like the people who try to protect against voltage drop get a "double whammy" of code restrictions whereas the folks who just let a long circuit run into impedance and voltage drop issues get to slide on by with their so-so circuitry, and that's the way of the code.
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