ECN Forum Forums Code Related Discussion NEC & other Code issues Tap rules

Here's the problem: I have a 400 ampere feeder (Fused at 400 amperew) and I'm taping to feed a 40 ampere load using a 60 ampere saftey switch and installing 40 ampere fuses to protect my 40 ampere load conductors. What size wire should I use from the feeder tap to the 60 ampere disconnect? (Using THHN in a damp location).

Forgot to tell you the tap is 8 feet long.

I would say #8

George you ask some interesting questions.

Assuming a lot here, but if all the requirements of 240.21(B)(1) are met I agree with Ryan 8 AWG copper.

Now one for you, or anyone, what size grounding conductor is needed from the point of the tap to the 60 amp disconnect?

Bob

Yes, but the question remains.

The tap conductors are the conductors feeding the equipment and so the EGC is #8. Table 250.122 requires a #3 EGC for a 400 amp OCPD, but #3 is larger than the conductors feeding the equipment and the EGC is not required to be larger than the conductors feeding the equipment.
Don

IMO a lot of people would size the conductor I am asking about based on the 40 amp fuse which would be 10 AWG copper which will be correct on the load side of that 60 amp disconnect.

I wanted to point out that the EGC on the supply side of the 60 amp disconnect will need to be based on the 400 OCP.

That would normally be a 3 AWG but for this application, will only need to be 8 AWG as the supply conductors are only 8 AWG.

I thought Georges example was perfect for pointing all this out, only a little off topic.

Bob

FWIW I would wire this disconnect up with 6 AWG, the length is short the difference in price and difficulty will not be a big deal.

Besides all I do is order the stuff, I do not pay for it.

JMO, not required, Bob

I agree with Iwire
#6 for the full load amps of the 60/as ( in the future you could change the load without rewire the whole mess )
#10 ground
all wire thwn ( damp location )

As long as the total wire lenth of the tap is less then 10'