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Old 03-30-2009, 07:20 PM   #1
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Default Voltage Drop
I could use some recommendations on how to do this project. I need 3, 20amp circuits to a LED sign for a business. It is approximately 1,240 from the Load center. To allow for voltage drop, each circuit would require 2/0 copper for a 20amp 120 volt circuit!!! Any suggestions for doing this a better way? Maybe a transformer? Thanks guys...
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Old 03-30-2009, 07:23 PM   #2
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Originally Posted by Absolutetruthz View Post
I could use some recommendations on how to do this project. I need 3, 20amp circuits to a LED sign for a business. It is approximately 1,240 from the Load center. To allow for voltage drop, each circuit would require 2/0 copper for a 20amp 120 volt circuit!!! Any suggestions for doing this a better way? Maybe a transformer? Thanks guys...
how many amps do the LEDs draw
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Old 03-30-2009, 07:24 PM   #3
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Well i run 480 volts out and step it down with a transformer its alot cheaper thats if you have 480 v .take care
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Old 03-30-2009, 07:25 PM   #4
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The sign seriously draw 20 amps on three circuits? What's the real draw?


Is this a freestanding sign, by chance? You can't run that many circuits to a structure. Gotta run one and put a panel out there. Is this one of those digital message boards, maybe? I've done 4 of them so far. Three double sided, and one single sided.
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Old 03-30-2009, 07:36 PM   #5
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I've done 4 of them so far. Three double sided, and one single sided.
Outstanding! You deserve a medal of some sort.
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Old 03-30-2009, 07:37 PM   #6
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Outstanding! You deserve a medal of some sort.
Yes, I am awesome, but you don't have to remind me.

The one's I've done were Street Smart brand. Mostly 48"x128"
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Old 03-30-2009, 07:47 PM   #7
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The sign seriously draw 20 amps on three circuits? What's the real draw?


Is this a freestanding sign, by chance? You can't run that many circuits to a structure. Gotta run one and put a panel out there. Is this one of those digital message boards, maybe? I've done 4 of them so far. Three double sided, and one single sided.
No, the sign calls for 3-20amp circuits, but it only draws a total of 32 amps. The voltage source I have available is 120/208 3phase. Yes it is one of those digital message boards.
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Old 03-30-2009, 08:56 PM   #8
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The sign seriously draw 20 amps on three circuits? What's the real draw?


Is this a freestanding sign, by chance? You can't run that many circuits to a structure. Gotta run one and put a panel out there. Is this one of those digital message boards, maybe? I've done 4 of them so far. Three double sided, and one single sided.

I know I'm going to regret this, but here goes.....

Why can't I run "that many" circuits toa structure? Is there a code reference?

That being said, putting in a 3 phase panel, with each circuit on a different phase would cut the voltage drop.

And 1200+' run? Wow, thats a lot of pull boxes!
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Old 03-30-2009, 09:58 PM   #9
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A couple of 5 kVA transformers would cost alot less than 1300' of 2/0 x 7 conductors. Boost 120 up to 480, send it to the sign on #12, then bring it back down to 120. Set a fuse block in the sign and feed the three 20 A inputs from there. Feed the first transformer from a 40 A breaker with some #8.
Last edited by InPhase277; 03-30-2009 at 10:35 PM.
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Old 03-30-2009, 10:01 PM   #10
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I know I'm going to regret this, but here goes.....

Why can't I run "that many" circuits toa structure? Is there a code reference?

That being said, putting in a 3 phase panel, with each circuit on a different phase would cut the voltage drop.

And 1200+' run? Wow, thats a lot of pull boxes!
225.30 is probably what Marc is thinking of. But there are a number of special conditions which may allow a sign to squeak by...
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Old 03-30-2009, 10:21 PM   #11
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Definately souds like transformers are the way to go
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Old 03-30-2009, 10:53 PM   #12
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A couple of 5 kVA transformers would cost alot less than 1300' of 2/0 x 7 conductors. Boost 120 up to 480, send it to the sign on #12, then bring it back down to 120. Set a fuse block in the sign and feed the three 20 A inputs from there. Feed the first transformer from a 40 A breaker with some #8.
wont there be a voltage drop between the two transformers, 1240ft apart?
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Old 03-30-2009, 11:02 PM   #13
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wont there be a voltage drop between the two transformers, 1240ft apart?
True, I didn't take that into account when I wrote #12. But at 480, there will be less than 9 A, if the sign draws 32 A. So you may need #6 between them. But you could get away with #8 and still be fine. Still cheaper than 2/0 times seven conductors!
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Old 03-30-2009, 11:15 PM   #14
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To heck with 480 go 600 Vac

120*32=3,840/600=6.2 amps

Solution:
1 conductor(s) per phase utilizing a 10 AWG Copper conductor will limit the voltage drop to 2.69% or less when supplying 6.2 amps for 1240 feet on a 600 volt system.
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Old 03-30-2009, 11:20 PM   #15
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True, I didn't take that into account when I wrote #12. But at 480, there will be less than 9 A, if the sign draws 32 A. So you may need #6 between them. But you could get away with #8 and still be fine. Still cheaper than 2/0 times seven conductors!
thanks for the help, Inphase. Could you lay out the math for me here, I'm not understanding how you came up with 9amps.thanks
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Old 03-30-2009, 11:27 PM   #16
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To heck with 480 go 600 Vac

120*32=3,840/600=6.2 amps

Solution:
1 conductor(s) per phase utilizing a 10 AWG Copper conductor will limit the voltage drop to 2.69% or less when supplying 6.2 amps for 1240 feet on a 600 volt system.
they make transformers that go from 208 to 600Vac?
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Old 03-30-2009, 11:30 PM   #17
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thanks for the help, Inphase. Could you lay out the math for me here, I'm not understanding how you came up with 9amps.thanks
Well, you said the sign pulls 32 A at 120 V. I rounded up to 35 A. 120 x 35 = 4200 VA. 4200/480 = 8.75 A @ 480 V.

And Brian is right. If you can find 600 V transformers, go with them. That will reduce the wire size between them even more.
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Old 03-30-2009, 11:36 PM   #18
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they make transformers that go from 208 to 600Vac?
They make transformers for everything, finding them readily available and at a reasonable price is the key. If you go with 208--->600 at the input, then you will either need a multi tap transformer at the sign end or a 600--->120. You don't want 208 at the sign.
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Old 03-30-2009, 11:36 PM   #19
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they make transformers that go from 208 to 600Vac?

120 to 600 and back down

Sola Hevi Duty up to 10 KVA

http://www.sola-hevi-duty.com/produc...selection.html

Group 2 : 600 Volt Primary, 120/240 Secondary, 60 Hz
kVA
CatalogNumber
Group I
Rolled Steel
CatalogNumber
Group II
Stainless Steel
Height
(inch)Width
(inch)Depth
(inch)Ship Weight
Approx. (lbs)Design
StyleElec
ConnPrimary
AmpsSecondary
AmpsNon-Encapsulated.100 HS10B100N/A64342210.167.833/.417.150 HS10B150 84452210.251.25/.625.250 HS10B25084482210.4172.08/1.04Encapsulated
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Old 04-01-2009, 06:48 AM   #20
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seems to me, the sign needs its own meter and service drop. What is the local utility saying?
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