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#88336 - 05/28/04 06:35 PM Tap rules
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
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).
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#88337 - 05/28/04 06:36 PM Re: Tap rules
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
Forgot to tell you the tap is 8 feet long.
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#88338 - 05/28/04 06:46 PM Re: Tap rules
Ryan_J Offline
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Registered: 08/19/03
Posts: 1355
Loc: West Jordan, Utah, USA
I would say #8
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#88339 - 05/28/04 07:02 PM Re: Tap rules
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
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
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Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#88340 - 05/28/04 09:20 PM Re: Tap rules
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
 Quote:
but shall not be required to be larger than the circuit conductors supplying the equipment.
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#88341 - 05/29/04 02:55 AM Re: Tap rules
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Yes, but the question remains.
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Massachusetts

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#88342 - 05/29/04 05:38 AM Re: Tap rules
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
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
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#88343 - 05/29/04 06:31 AM Re: Tap rules
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
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
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#88344 - 05/29/04 06:37 AM Re: Tap rules
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
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
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Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#88345 - 05/29/04 12:51 PM Re: Tap rules
dfe Offline
Member

Registered: 05/25/04
Posts: 18
Loc: n.h. calif. usa
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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