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Old 06-21-2010, 09:59 PM   #1
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Default what size wire for a 100 amp subpanel 200' away from the main service?

i have a 200 amp service wondering what size wire i need for a 100 amp subpanel 220' away from the main service? also what size equip. ground. i got with a 5% vd 1/0 cu and 3/0 at 3% drop. i also got 3/0 al at 5% and 300 at 3
%. this seems a little high. i was figuring to use the 5% drop and do a 3/0 al with a number 2al ground. does this sound right??

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Old 06-21-2010, 10:30 PM   #2
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The sub panel is 100 amp but what is the calculated load. If you are looking for the wire size for 100 amps at 240 then 2/0 alum. would work. For copper you need #1.

For the EGC then look at T. 250.122


Last edited by Dennis Alwon; 06-21-2010 at 10:45 PM.
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Old 06-21-2010, 10:43 PM   #3
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^^^^What Dennis said.
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Old 06-21-2010, 10:47 PM   #4
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Remember there is no NEC requirement to wire for VD. It is a good idea and good design but not required.

BTW, I believe the same wire sizes are good for 208, 3 phase also.
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Old 06-21-2010, 10:57 PM   #5
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Its for a garage at my friends house there is no calc. Load as of yet but there will prob be 15-20 lights a compressor, mayb a 220v motor for a lift. And acouple outlets for grinding wheel and stuff like that but nothing major. So 2/0 would be plenty for this?
As for the egc do I have to take into acount the length and bump it up a couple sizes like the feeders?? Or just go with the 100 amp size??
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Old 06-21-2010, 11:05 PM   #6
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Quote:
Originally Posted by zss42002 View Post
Its for a garage at my friends house there is no calc. Load as of yet but there will prob be 15-20 lights a compressor, mayb a 220v motor for a lift. And acouple outlets for grinding wheel and stuff like that but nothing major. So 2/0 would be plenty for this?
As for the egc do I have to take into acount the length and bump it up a couple sizes like the feeders?? Or just go with the 100 amp size??
If you increase the wire size, you must increase the ground size. 250.122(B).
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Old 06-21-2010, 11:07 PM   #7
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If you increase the wire size, you must increase the ground size. 250.122(B).
Good point
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Old 06-21-2010, 11:10 PM   #8
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Ken will calculate the egc for you for a few bucks.
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Old 06-21-2010, 11:14 PM   #9
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I think you would need a #4 copper EGC-- send Ken $10
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Old 06-21-2010, 11:17 PM   #10
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I think you would need a #4 copper EGC-- send Ken $10

Man.... what a scheme.... get everyone on the forum to send me a ten-spot! I'm rich!
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Old 06-22-2010, 02:20 AM   #11
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Man.... what a scheme.... get everyone on the forum to send me a ten-spot! I'm rich!
just as long as dinner is at your house!

~Matt
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Old 06-23-2010, 08:45 PM   #12
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one million mcm
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Old 06-23-2010, 09:10 PM   #13
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just as long as dinner is at your house!

~Matt

Hey, if all 13,329 members sent me a 10-spot, I'd definitely have a shindig at my place.
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Old 06-23-2010, 09:50 PM   #14
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Hey, if all 13,329 members sent me a 10-spot, I'd definitely have a shindig at my place.
lets have a raffle

everyone who wants to put up ten bucks

pick one winner
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Old 06-24-2010, 09:52 AM   #15
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The more load, the more the voltage drop. Mike Holt has a calculator you can download.

http://www.mikeholt.com/technical.ph...calvoltagedrop


#3 THHN\THWN copper is good for 100 amps at 75 degrees.

With a load of 50amps at 240volts at 200' with #3 copper Mike Holts voltage drop tool says you have 2.1% voltage drop.

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