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#12897 08/20/02 10:22 PM
Joined: Apr 2002
Posts: 914
E
Member
Help! I'm working on a bid and my "handy" electric calculator is giving me conflicting answers on wire size for a long run. The run is almost 400 feet(up and down included) from the main panel to the sub panel. 100 amps 120/208 3 phase. Using copper THHN and 3% VD, what size wire?
While we're at it, how much would you bid? Most of the run is 25ft in the air and you need to add 3 30 amp 3 phase outlets to plug in equipment near the new sub. The panels are seimens bolt in and the conduit needs to bew EMT, you provde the lift. Thanks!

Joined: Apr 2002
Posts: 21
J
jo Offline
Member
10,700 #2 wire 2"emt

Joined: Jul 2002
Posts: 74
S
Member
With a full load and 3.1% you need to run a 2/0. 3/0 gets you douwn to a 2.5% v/d..
To early in the morning to help with the quote..
SC John.

Joined: Dec 2000
Posts: 4,288
Member
Ditto SCJohn,
2.55% VD with 3/0
2" EMT

Joined: Apr 2002
Posts: 21
J
jo Offline
Member
Sorry
3/0 is correct

Joined: Jan 2002
Posts: 163
D
Member
Feedback please - these VD calculations to determine the need for 3/0 conductor is based on a 100A draw - in truth this panel will not be pulling 100A...prob. won't even be pulling 90A....if you use 90A in your calculation your conductor size drops to 2/0. Not only does this lower the matl. cost it sure makes pulling into that 2" conduit a lot easier. My opinion is this: if you're going to be pulling more than 80A from a 100A panel, you should be upsizing it to begin with.

Joined: May 2001
Posts: 717
G
Member
Your calculation is based on Article 220. That is where your amps for your VD calc should come from.

Joined: Apr 2002
Posts: 914
E
Member
Thanks to everyone! My ElectriCalc was telling me 3/0 CU, but I didn't want to believe it. I mean 4/0 AL is good for 200. The actual run is more like 370ft and I can live with just over 3%VD, so I did the quote with 2/0, although my gut tells me that they will never pull more than 50 or 60 amps in which case #1CU would be fine. I gave the bid the way I would want it, if I lose it to someone using #1 or #2, then so be it. Thanks Guys

Joined: Dec 2000
Posts: 4,288
Member
George is right. Use 220, not your gut feeling (I thought you said 100 amp load). [Linked Image]

Joined: Apr 2002
Posts: 914
E
Member
electure, I ignored my gut feeling and went with the max, but I doubt my competion did, that's what I was saying. Acutally when you add the 3 pieces of equipment, the total max amps is 58 (22,22&14) and will all run at the same time. But this is for a 100 amp sub panel and someone in the future could add more equipment or even another sub panel off of this one. Therefore I wanted to make sure the wire could handle max load without substanial VD.


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