Fault current-the other side

[ptonsparky]

Promised myself to do the FC calcs.

Small system 480v single phase, 1000 feet of #2 Al (increasing it from #4), we will be lucky to get enough to blow a 30 amp fuse in less than 3 seconds. That is a lot of arc and spark time.

 

[gar]

161102-2210 EDT

#2 copper at 20 C is 0.156 ohms. A loop of 2000 ft is 0.312 ohms. Multiply by 1.68 for aluminum and loop resistamce is 0.52 ohms. At 480 V RMS current is 480/0.52 = 920 A. Somewhat less if the wire is hotter. 900 A on a 30 A breaker would be instantaneous trip, about 8 mS.

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[Cow]

161102-2210 EDT

#2 copper at 20 C is 0.156 ohms. A loop of 2000 ft is 0.312 ohms. Multiply by 1.68 for aluminum and loop resistamce is 0.52 ohms. At 480 V RMS current is 480/0.52 = 920 A. Somewhat less if the wire is hotter. 900 A on a 30 A breaker would be instantaneous trip, about 8 mS.

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He mentioned aluminum gar. But you gave him the formula to follow regardless, I suppose.

 

[ptonsparky]

161102-2210 EDT

#2 copper at 20 C is 0.156 ohms. A loop of 2000 ft is 0.312 ohms. Multiply by 1.68 for aluminum and loop resistamce is 0.52 ohms. At 480 V RMS current is 480/0.52 = 920 A. Somewhat less if the wire is hotter. 900 A on a 30 A breaker would be instantaneous trip, about 8 mS.

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POCO sent me an updated FC of 740. L-L instead of L-N. Results @ 1000' AL is .008 seconds for a 30 amp FRS according to the curve. Not bad GAR, we might get the impression you know what you are doing, eventually. I have those resistances in my VD spreadsheet, all I had to do was think a bit.:dunce: It will be a simple add.

The fun part is adding the ROTO PHASE at this point and going another 900' of 4 AL. Ignoring it, we end up with about 157 Amps. 10 seconds for the 30 Amp Fuse.