ECN Forum Forums General Topics of the Trade General Discussion Area How long can a circcuit be?

Ray'
Oops,
That should have read 15kA, not sure how that slipped under the radar.
Just got a new laptop and the keyboard is VERY different to my normal computer keyboard.
Fault currents are very high at work, due to the size of the mains installed and the proximity of transformers.
The PoCo used more tranny's than usual with this area of town, to maintain the voltage at a respectable level, given the loads involved.

Steve,
My numbers say that 8' (4' of NM) of 14 will permit 4777 amps to flow if the system can supply it. Yes that is less than 5000 amps, but the 1/2 cycle damage point for #14 is 2384 amps.
So there is never a need for a small breaker with an AIC greater than 5,000 amps?
Don

[This message has been edited by resqcapt19 (edited 11-03-2006).]

Just for fun, try doing a voltage drop calculation on a 150 foot run of 14 with a 12 amp load.

Well, that depends greatly on the distribution system and the size of the transformer. In this example, yeah, 5KAIC would be all that's required. But we could easily come up with another example (say, a 15A breaker on a 400A panel bus-fed from a 3000A switchboard/1MVA transformer) feeding a receptacle 6" from the panel. In THIS case, there is potential to exceed 5KAIC and damage the cable.

But in a typical residence, shorting out the receptacle? Not likely at all. The engineer really has to calculate all this and specify the KAIC rating of the breakers if it's expected to be an issue.

[This message has been edited by SteveFehr (edited 11-07-2006).]