sub panel from house 200 amp breaker box


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Old 01-17-14, 03:18 PM
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sub panel from house 200 amp breaker box

I have a detached shed 180 feet from actual main breaker box. want to use a 100 amp breaker and if a #6 can be used.

If I go with #8 can a 60 Amp breaker be used?
 
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Old 01-17-14, 03:22 PM
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#8 is only good for 40 amps but at 180 feet if your load is great enough you may need to go to #6 on a 40 amp breaker.
 
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Old 01-17-14, 03:25 PM
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Welcome to the forums!

What will the connected load in the shed be?
 
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Old 01-17-14, 03:53 PM
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I hate to bring the subject of voltage drop up again, but it really hasn't been resolved. Is 5% a general rule of thumb, or does NEC explicity set restrictions on the amount of allowable drop? 180 feet is a pretty good run. #8 copper will give the OP a DC drop of 16.8V (14%) at full load!
 
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Old 01-17-14, 05:55 PM
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Is 5% a general rule of thumb, or does NEC explicity set restrictions on the amount of allowable drop?
Voltage drop is not specified by the NEC, but 3% maximum for a feeder is suggested; 5% maximum for both feeder and branch circuit is recommended.

Don't Let Voltage Drop Get Your System Down | Code Basics content from Electrical Construction & Maintenance (EC&M) Magazine

As far as I know, this is not something that is revised by each code panel every three years.
 
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Old 01-18-14, 05:43 AM
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Voltage drop is not specified by the NEC, but 3% maximum for a feeder is suggested; 5% maximum for both feeder and branch circuit is recommended.
That being said, it's probably fine to use the expected maximum current draw when calculating voltage drop, as opposed to the subpanel rating. However, it would be wise to use the panel rating to ensure voltage drop is a non-issue. Better to run a slightly larger gauge to be sure.
 
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Old 01-18-14, 07:12 AM
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Better to run a slightly larger gauge to be sure.
Spoken like a true engineer!
 
 

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