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#88336 05/28/04 09:35 PM
Joined: Jan 2004
Posts: 1,507
G
Member
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).


George Little
2017 / 2014 NEC & Related Books and Study Guides
#88337 05/28/04 09:36 PM
Joined: Jan 2004
Posts: 1,507
G
Member
Forgot to tell you the tap is 8 feet long.


George Little
#88338 05/28/04 09:46 PM
Joined: Aug 2003
Posts: 1,374
R
Moderator
I would say #8


Ryan Jackson,
Salt Lake City
#88339 05/28/04 10:02 PM
Joined: Jan 2003
Posts: 4,391
I
Moderator
George you ask some interesting questions. [Linked Image]

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


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#88340 05/29/04 12:20 AM
Joined: Nov 2000
Posts: 2,148
R
Member
Quote
but shall not be required to be larger than the circuit conductors supplying the equipment.


Don(resqcapt19)
#88341 05/29/04 05:55 AM
Joined: Jan 2003
Posts: 4,391
I
Moderator
Yes, but the question remains. [Linked Image]


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#88342 05/29/04 08:38 AM
Joined: Nov 2000
Posts: 2,148
R
Member
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


Don(resqcapt19)
#88343 05/29/04 09:31 AM
Joined: Jan 2003
Posts: 4,391
I
Moderator
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, [Linked Image] only a little off topic.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#88344 05/29/04 09:37 AM
Joined: Jan 2003
Posts: 4,391
I
Moderator
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. [Linked Image]

JMO, not required, Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#88345 05/29/04 03:51 PM
Joined: May 2004
Posts: 19
D
dfe Offline
Member
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'

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