# Wire Size for Volatge Drop



## Speedy Petey (Jan 10, 2007)

This is a very common thing to do, to run a single phase feeder off a three phase panel.


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## brybedo (Nov 16, 2007)

Thanks for the reply Petey... BUT, do I have to treat it as a SINGLE PHASE application since I'm only sending an A & B Leg (No C) to my sSub Panel and adjust my wire size to a Single Phase Application? Remember, my distance is 750 feet. Voltage Drop calculators are telling me I need to size my wire to 300KCMIL for 3 Phase and 400KCMIL when I treat it as a single Phase....?


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## JohnJ0906 (Jan 22, 2007)

brybedo said:


> Thanks for the reply Petey... BUT, do I have to treat it as a SINGLE PHASE application since I'm only sending an A & B Leg (No C) to my sSub Panel and adjust my wire size to a Single Phase Application? Remember, my distance is 750 feet. Voltage Drop calculators are telling me I need to size my wire to 300KCMIL for 3 Phase and 400KCMIL when I treat it as a single Phase....?


You will have to upsize for sure at that distance.

I would calculate at single phase.


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## Speedy Petey (Jan 10, 2007)

Two phases of a three-phase service is single phase no matter how you look at it.


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## JohnJ0906 (Jan 22, 2007)

Speedy Petey said:


> Two phases of a three-phase service is single phase no matter how you look at it.


Over at Mike Holt's, some poor guy asked why we call 2 legs of a 3 phase system "single phase"

The engineers got hold of it, and the thread is now over 600 posts...


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## brybedo (Nov 16, 2007)

Thats the way I see it... try telling that to your expert physicist customer. Any body else care to back me up? please???


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## brybedo (Nov 16, 2007)

Where's that post?!!!!?? I need it!


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## JohnJ0906 (Jan 22, 2007)

brybedo said:


> Where's that post?!!!!?? I need it!




http://forums.mikeholt.com/showthread.php?t=96673

620 posts and counting.

God, I love engineers... :laughing:


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## Speedy Petey (Jan 10, 2007)

JohnJ0906 said:


> 620 posts and counting.


To quote Bob Badger from post #2:


iwire said:


> Your best bet is to just accept it.
> 
> This question is bound to generate a ton of responses. :grin:


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## JohnJ0906 (Jan 22, 2007)

Speedy Petey said:


> To quote Bob Badger from post #2:


And he hit it right on the head, didn't he? :laughing:


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## Magic Electric (Nov 24, 2008)

In the uk you will see on test certs . schedule of results that when you do a ir test it asks for the result between phase and phase and not phase and n

are they wrong too....lol


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## Magic Electric (Nov 24, 2008)

as for the cable calculation. i would do it as single phase and make sure not to that the volt drop stays within 4% of the supply voltage. if it is not then you will need to up the cable size


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## Stan Mason (Oct 30, 2008)

this is what I use it's pretty cool http://www.ifigure.com/engineer/electric/electric.htm


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## nolabama (Oct 3, 2007)

why is the high leg C phase? see 408.3 (E) doesnt sound like you fit the execption


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## Stan Mason (Oct 30, 2008)

nolabama said:


> why is the high leg C phase? see 408.3 (E) doesnt sound like you fit the execption


I have never seen it as C phace it's always the B phase


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## micromind (Aug 11, 2007)

Years ago it was very common to have the high leg phase C. 

It was also common to have an existing single phase installation, and add another panel for 3 phase needs. You'd change the meter base, sometimes just the meter mounting block, run another wire from the new panel up the mast, and the POCO would hang another pot on the pole. 

Since the existing single phase panel was usually black and red (A and B), the high leg was made to be blue (C). Also, on a feed-through meter, the high leg is phase C. 

Rob


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## mister cheeks (Feb 8, 2009)

brybedo said:


> My existing service is a 200 Amp 3 Phase 120/240-Delta configuration with C being the High Leg or "stinger" . I've got to get 100 Amps to a barn 750' away. I only need 120/240V single phase to this barn. Can I drop my C Leg and still use 3/0 wire or do I need to upsize my wire even larger to accomodate for voltage drop and the lack of that C Leg. Any help would be greatly appreciated.
> 
> Bryan


 
i cant believe u guys still use 120/240 delta.why dont you guys use 120/208 y.That c phase ,what we call a bastard leg just means a hole lot of trouble.Thats not the proper way to do things,there taking the c phase off the middle of the windings to create 208 to ground,off that phase.wow very scary practice.very old school.


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## Speedy Petey (Jan 10, 2007)

Most times we don't have a choice. It's what is there.


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## Chris Kennedy (Nov 19, 2007)

nolabama said:


> why is the high leg C phase? see 408.3 (E) doesnt sound like you fit the execption


High leg would be at C at meter base. POCO meters are set up this way. High leg at B main disco as per 408.3(E).


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