I am building a new shop that will have it's own 200A service. New pole meter and disconnect at street. My total feeder length will be about 475 feet first 260 overhead the last 215 buried in conduit. what size cable do I need overhead and what size UG? I have got no solid answers from power company, electrical supplier, or local electricians. Everyone says depends or use whatever you want.
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Cable sizing
- Thread starter gbrett
- Start date
Doesn't the power company handle the overhead line?
wyliesdiesels
Well-known member
Doesn't the power company handle the overhead line?
His meter is at the street so the wire he is speaking of is on the load side of the meter and the PoCo doesnt own that...
I am building a new shop that will have it's own 200A service. New pole meter and disconnect at street. My total feeder length will be about 475 feet first 260 overhead the last 215 buried in conduit. what size cable do I need overhead and what size UG? I have got no solid answers from power company, electrical supplier, or local electricians. Everyone says depends or use whatever you want.
I'd strongly recommend that you move the transformer closer to your building. 475 feet is a very long way and subject to a lot of voltage drop. Normally you'd use 250 mcm aluminum for 200 amps to a building, you'd need twice that size (500 mcm) to keep your voltage drop below the standard 3%.
I'd have the utility lines run the 260 feet overhead to the last pole, then have the line go down the pole and get buried to come up to a pad transformer a handful of yards from your building. Then I'd run the service from the transformer underground to the building, have the meter and disconnect on the outside of the building, and then have the service enter the building behind the disconnect.
wyliesdiesels
Well-known member
I'd strongly recommend that you move the transformer closer to your building. 475 feet is a very long way and subject to a lot of voltage drop. Normally you'd use 250 mcm aluminum for 200 amps to a building, you'd need twice that size (500 mcm) to keep your voltage drop below the standard 3%.
I'd have the utility lines run the 260 feet overhead to the last pole, then have the line go down the pole and get buried to come up to a pad transformer a handful of yards from your building. Then I'd run the service from the transformer underground to the building, have the meter and disconnect on the outside of the building, and then have the service enter the building behind the disconnect.
Good idea and i wouldve suggested the same but i doubt the OP has that option or its too costly...
I'd strongly recommend that you move the transformer closer to your building. 475 feet is a very long way and subject to a lot of voltage drop. Normally you'd use 250 mcm aluminum for 200 amps to a building, you'd need twice that size (500 mcm) to keep your voltage drop below the standard 3%.
I'd have the utility lines run the 260 feet overhead to the last pole, then have the line go down the pole and get buried to come up to a pad transformer a handful of yards from your building. Then I'd run the service from the transformer underground to the building, have the meter and disconnect on the outside of the building, and then have the service enter the building behind the disconnect.
Would love to but they said set a pole at street within 90 feet of their transformer pole and after that it's my problem. they did the same thing last time I built a shop but that time was over 600 feet and all underground. Don't recall what size wire I ran that time but the power company specified it for me and gave it to me. I was under the impression the overhead would allow me to use a smaller wire as ampacity ratings are higher in open air. Voltage runs high here so I may be able to get away with a bit more voltage drop probably will have about 128 volts at meter on each leg.
Your never going to use 200A, makes no sense to size by a fantasy load it is better to size by the actual load.
I agree I will likely never use that much 1 man shop I think I am more worried about voltage drop than amps. beyond lighting and general plugs I have 5hp air compressor 2 post lift and 5 welders. Although none of those should be running at the same time. I will likely move the feed for up to 10hp irrigation pump to the new shops service and off of the house feed. When the pump runs it is 24/7 for 5 or 6 days so it would run with the shop equipment. I think worst case would be pump @60A welder @50A and air compressor @30A plus lights and plugs running at once. those are breaker sizes not actual loads.
To keep your voltage drop to 3% or less as recommended (but not required) by the NEC, using aluminum wire:
3/0: 60 amp maximum current draw
4/0: 75 A
250 mcm: 89 A
300 mcm: 107 A
350 mcm: 125 A
400 mcm: 143 A
500 mcm: 178 A
250 mcm wire is the smallest allowed for a 200 amp service entering in conduit for an outbuilding unless the meter disconnect or main breaker is smaller than 200 A. You would need a 150 for the 3/0 or 4/0. You can use smaller wires in free air than in conduit per code, but your issue is the wire with enough amperage capacity already has a lot of voltage drop. Making them smaller would only make the problem worse.
The irrigation pump will use a constant 40-45 A when it runs unless the motor is grossly oversized for the pump. An air compressor on a 30 A circuit will draw 25 A or less and is an intermittent load, and the welder is a very intermittent load, and many are reported to draw only 20-30 A.
I would strongly reconsider putting the irrigation pump on the outbuilding service as it draws a lot of power. If that is gone, you should be fine running 250 mcm wire as that lets you draw 89 amps and not have too much voltage drop. 90 A is a very often used outbuilding service size here. If you want to run the pump off this panel, I would run 350 mcm wire to give some extra capacity.
3/0: 60 amp maximum current draw
4/0: 75 A
250 mcm: 89 A
300 mcm: 107 A
350 mcm: 125 A
400 mcm: 143 A
500 mcm: 178 A
250 mcm wire is the smallest allowed for a 200 amp service entering in conduit for an outbuilding unless the meter disconnect or main breaker is smaller than 200 A. You would need a 150 for the 3/0 or 4/0. You can use smaller wires in free air than in conduit per code, but your issue is the wire with enough amperage capacity already has a lot of voltage drop. Making them smaller would only make the problem worse.
The irrigation pump will use a constant 40-45 A when it runs unless the motor is grossly oversized for the pump. An air compressor on a 30 A circuit will draw 25 A or less and is an intermittent load, and the welder is a very intermittent load, and many are reported to draw only 20-30 A.
I would strongly reconsider putting the irrigation pump on the outbuilding service as it draws a lot of power. If that is gone, you should be fine running 250 mcm wire as that lets you draw 89 amps and not have too much voltage drop. 90 A is a very often used outbuilding service size here. If you want to run the pump off this panel, I would run 350 mcm wire to give some extra capacity.
wyliesdiesels
Well-known member
I agree I will likely never use that much 1 man shop I think I am more worried about voltage drop than amps. beyond lighting and general plugs I have 5hp air compressor 2 post lift and 5 welders. Although none of those should be running at the same time. I will likely move the feed for up to 10hp irrigation pump to the new shops service and off of the house feed. When the pump runs it is 24/7 for 5 or 6 days so it would run with the shop equipment. I think worst case would be pump @60A welder @50A and air compressor @30A plus lights and plugs running at once. those are breaker sizes not actual loads.
well that certainly changes things quite a bit. A 10HP motor is quite a load for a single phase service especially over almost 500' of wire. a motor that size is drawing 40 something amps by itself...
your other option is to go with a pair of 480-240/120v transformers. Reverse feed one at the meter, then you can use reduced size wire for the feeder from the meter to the shop. you may be able to find a used pair for around $1000.... the wire for this could run you more than $3K so transformers would save a bit....
What the hell are you irrigating that uses a 10hp pump?
Hay field. That's not really a big pump as far as irrigation pumps go I have a 60HP pump at the main farm. It is 480 3 phase though.