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Old 10-25-2011, 05:47 PM   #1
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I would like to put a 100 amp subpanel in the barn what size wire should I use and should use the same type of wire in the house as I do outside /overhead? Thanks

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Old 10-25-2011, 08:42 PM   #2
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When you run a wire a long distance, you get "voltage drop". If you use a larger gauge wire, the voltage drop is less. This also depends on the load (watts or amperage) of what you will be running.

For example the voltage at the house might be 120 volts, but with a long distance, small gauge wire, and heavy load, the voltage at the end might be only 80 volts!

This is the same problem as trying to run an air compressor on a 100 ft. small gauge extension cord. It just hums and does not run.

Google "voltage drop calculator" to see what different size wires will do.

Also check with your local electrical inspector's office as to other requirements. (Where you get electrical permit to do this...)

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Old 10-25-2011, 08:47 PM   #3
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The distance is a major factor in determining wire size in addition to the amperage of the panel. Give us a bit more information.
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Old 10-25-2011, 08:47 PM   #4
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If you go aerial you will need quadflex, not triplex cable. New panel installs require a 4 wire feeder.

You would also need 4 conductors in an underground feeder.
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Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
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Old 10-25-2011, 09:02 PM   #5
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The distance is a major factor in determining wire size in addition to the amperage of the panel.
Common sense-yes. NEC-no.
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Old 10-25-2011, 09:24 PM   #6
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I would like to put a 100 amp subpanel in the barn what size wire should I use and should use the same type of wire in the house as I do outside /overhead? Thanks
Depends on how many amps you plan on using, and what brand they are. Are you expecting to only use those amps during the day time, or night time? Does your power company manufacture those amps by coal, natural gas, or nuclear. Are you only expecting to use those amps for allowing you to use a light to see by, or to actually benefit you in some other form or matter.

Those questions to those amps need to really be answered. And keep in mind, purchasing your panel from either Lowe's, Home Depot or elsewhere will also determine how good those amps will be, when they pass through the panel on their way to meet other amps in the space of the structure that you wish to use them in.
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Old 10-25-2011, 09:57 PM   #7
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Depends on how many amps you plan on using, and what brand they are. Are you expecting to only use those amps during the day time, or night time? Does your power company manufacture those amps by coal, natural gas, or nuclear. Are you only expecting to use those amps for allowing you to use a light to see by, or to actually benefit you in some other form or matter.

Those questions to those amps need to really be answered. And keep in mind, purchasing your panel from either Lowe's, Home Depot or elsewhere will also determine how good those amps will be, when they pass through the panel on their way to meet other amps in the space of the structure that you wish to use them in.
Er....Greg, WTH are you talking about?
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Old 10-25-2011, 10:05 PM   #8
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Common sense-yes. NEC-no.
I thought common sense was encouraged here........
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Old 10-25-2011, 10:16 PM   #9
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Thought that I would have some fun with it. They did ask what size of wire for the subpanel, but never specified use, so thought that I would see if I could get their attention. Someone has to.
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Old 10-25-2011, 10:23 PM   #10
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I thought common sense was encouraged here........
Yes, it is and I support it, but voltage drop is actually specifically addressed as code in only two articles. 647 and 695.

I can only address questions as what to code requires, I can recommend better ideas and solutions-but code is law- unfortunately common sense is not.
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Old 10-25-2011, 10:25 PM   #11
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Thought that I would have some fun with it. They did ask what size of wire for the subpanel, but never specified use, so thought that I would see if I could get their attention. Someone has to.
Okay, cool.
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Old 10-26-2011, 05:54 AM   #12
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I am not sure what I'll be running no big plans as of now, some lighting and heat lamps and in the future an air compressor. The amount of line approx from panel to the outside of house 75 feet, from house to barn 65 feet, from outside of barn to subpanel 40 feet. I live in pa.
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Old 10-26-2011, 08:21 AM   #13
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It is hard to guess what someone needs without knowing what the load is going to be. Do you want a full bore 100 amp feed and panel? Is 90 or 80 enough?
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Old 10-26-2011, 09:14 AM   #14
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No I don't necessarily need a full 100 just figured I would go high while I am at it.
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Old 10-26-2011, 10:56 AM   #15
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You will need to know the total length of the wire. Say running from a panel in your house... Up from panel, across to where it will exit house, to barn, then across to where the subpanel will be, then down.

What is that length?

Then think of everything you would ever have on all at the same time?

(Think heating or air conditioning? Air compressor? Welder? Other power tools? Refrigerator or freezer? Recreational Vehicle?)

What might you possibly use your barn for in the future?

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