S coiling 500 in a cable tray to lower resistance

[Eddy Current]

Has anybody ever heard of doing this. Somebody i work with said that the guys he helped pull wire with to a switch gear coiled the wire up to lower resistance. I think somebody is putting somebody on.

 

[jusme123]

.....and how does this lower resistance? You do not coil 500's

 

[kwired]

longer the conductor the more its resistance. This can possibly be helpful for lowering the available fault current though. If you are close on max rating of a breaker just 10 feet of conductor can sometimes make a big difference. S bending 500's to get 10 more feet of length takes a little room to do so.

 

[Eddy Current]

longer the conductor the more its resistance. This can possibly be helpful for lowering the available fault current though. If you are close on max rating of a breaker just 10 feet of conductor can sometimes make a big difference. S bending 500's to get 10 more feet of length takes a little room to do so.

I think thats what he said they S coiled was about 10 feet. Ive never heard of anybody doing this.

 

[Jraef]

I think thats what he said they S coiled was about 10 feet. Ive never heard of anybody doing this.

It's done, but not often. It only helps if, as kwired said, you are right on the ragged edge of a breaker's interrupt capacity (AIC rating) and need to INCREASE the resistance in order to lower that Available Fault Current at the breaker terminals. But not only does it take a lot of room to S coil 500's (4-5X the cable OD for THHN per bend), don't forget that you have to strap / brace it as well. You can't just lay it in the S curve in a tray somewhere. If there was a fault, that cable would start whipping around destroying things. Not to mention the extra cost of 60 extra feet of 500kCMIL THHN!