Tapping off the main

[Ellement]

I'm under the impression that it's OK to tap off a 200 amp or 400 amp trough to feed a 30,40 or 60 amp switch, thus using #10, #8 and #6 accordingly. Is this correct? If so why is there no concern for the high available current that has the potential to cross the wire before the switch,usually within 12" to 36" of the trough?

I have seen a lot of installations recently with a similar arrangment in 100Amp panels, Ex.: Heat pumps and AC units being tapped off of the main buss terminals after the 100amp breaker to be fed to a sub panel (service switch) below the panel. But the tap off the 100amp main is done with a #10, #8 or a #6 accordingly. This can't be OK?
Please let me know your opinion and any code ref. you may have. Thanks
.

[electric-ed]

Yes, tapping as you have described it is OK if Rule 14-100 is followed. I can remember when fused switches fed from a splitter trough was a common type of distribution in small commercial installations.

Rule 14-100 has seven paragraphs, but (b) and (c) are the ones that cover most cases similar to what you described.

Why is it OK? I think it's a matter of being practical. You can't easily get 4/0 wire into the terminals of a 60 amp switch, if you know what I mean.
Generally, 14-100 requires the "over-protected" conductors to be short in length, well protected from damage, and terminate in the correctly rated overcurrent protection.

Ed

<font color="#a62a2a" size="1">[ October 09, 2003 04:24 PM: Message edited by: electric-ed ]</font>