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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
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Forgot to tell you the tap is 8 feet long.
George Little
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Ryan Jackson, Salt Lake City
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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
Bob Badger Construction & Maintenance Electrician Massachusetts
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but shall not be required to be larger than the circuit conductors supplying the equipment.
Don(resqcapt19)
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Yes, but the question remains.
Bob Badger Construction & Maintenance Electrician Massachusetts
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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)
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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
Bob Badger Construction & Maintenance Electrician Massachusetts
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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
Bob Badger Construction & Maintenance Electrician Massachusetts
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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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