Gauge wire needed for 50 Amp Load

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Old 03-27-04, 10:54 PM
RamTruckMan
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Lightbulb Gauge wire needed for 50 Amp Load

I want to run electric to my steel building located 600 feet from the house. I want to run a welder. The welder has 50 amp plug.
What qauge aluminum wire do a need for a 50 amp maximum load at 600 feet.
 
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Old 03-28-04, 10:37 AM
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The size of wire needed will depend upon the maximum load, which you have not specified. You are going to have to look at the welder manual and figure out what the maximum load is.

Because welders have duty cycle limitations, the maximum load is allowed to be greater than the normal maximum ampacity of the connectors used to feed the welder. So the fact that the welder has a 50A plug really isn't enough to go on.

If we _presume_ a 50A maximum load, and we presume a 240V supply, then for a 600 foot run you will need 1/0 aluminium conductors. Additionally, because you are increasing the size of your circuit conductors for voltage drop, you will also need to increase the size of your equipment grounding conductor. The normal #8 Al equipment ground will need to be upsized to a #4 Al.

-Jon
 
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Old 03-28-04, 11:26 AM
RamTruckMan
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Wire Size

Thanks for the quick reply. Couldn't I resolve the grounding issue by putting a ground at the breakbox at the building?
 
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Old 03-28-04, 12:30 PM
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That depends on many factors.

1) Do you intend to install a subpanel at the other building? If so, that I would recommend making the wire larger so that you can run other things along with the welder. You will need to figure out the _total_ load in order to determine what sort of wire you need. If you plan on running _separate_

2) Are there any additional metallic paths between the buildings. By metallic paths I mean anything from a telephone wire to a metal water pipe to a fence to metal conduit for carrying the wires to the outbuilding.

If there are _no_ metallic ground paths between the buildings, then you can do the subpanel in the outbuilding like a main panel, meaning that you bring in the two hots and the neutral, but don't bring in an equipment ground, and you ground the neutral in the panel. In this case you have to follow all of the grounding rules for a service entrance.

If there are any metallic paths between the buildings, then you have to wire the subpanel like a normal subpanel, with a separate equipment ground and neutral conductor coming in, and separate ground and neutral bus bars.

-Jon
 
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Old 03-28-04, 06:49 PM
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Grounding electrode required either way

Just so it is clear whether you run an equipment grounding conductor with the feed to the building or not you will still have to install a grounding electrode system at your out building.

If the structural steel is effectively grounded you can make your grounding electrode conductor termination to it. It is likely to be effectively grounded if the framing anchor bolts were set into concrete that is reinforced with rebar. The code requires you to make the connection even if the frame is not effectively grounded in order to prevent the frame from ever remaining energized should a fault occur between the wiring and the frame. If the frame of the building is not effectively grounded the you should take steps to ground it if lightning is at all common in your area.

If the floor or the footer is reinforced with rebar and you have a place to attach a grounding electrode conductor to it you should. That is called a concrete encased electrode and it usually offers a very low ground impedance.

The minimum grounding electrode system for the outbuilding is two driven rods or a single rod with a measured impedance of twenty five ohms or less. Even with two rods the impedance of that system will be high. If the soil is too rocky for driven rods you are permitted to bury the rods in a trench that is two and one half feet deep. Even when laid flat they must be kept six feet apart.

If your feed will be buried than you have an opportunity to improve the grounding of both buildings. The minimum depth of a direct buried circuit of that ampacity is two feet. If you make the trench at least two and one half feet deep; three feet is better; and run a bare number two copper conductor as your equipment grounding conductor you will have the same effect as having installed a ground ring at both buildings. This will insure that you have a relatively low grounding impedance for both buildings. A ground ring is defined as a "ring encircling the building or structure, in direct contact with the earth, consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 2 AWG." Many inspectors will not recognize it as an electrode if it is laid in the feeder trench rather than circling the building. That is easily remedied by driving the two rods as window dressing. There is an advantage to having the number two copper encircle the building. It allows you to tap off the ring with conductors to ground the metal framing uprights to the ring if they are not already effectively grounded by their anchor bolts. A ring around the building is less wire and more trenching than laying 600 feet of number two in the feeder trench that you have to dig anyway.
--
Tom Horne
 
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