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Old 06-12-2010, 02:34 PM   #1
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sub panel in work shop.


Hello, I know this question has been asked before, so here it goes. I want to put a 240v 70amp service in my back yard work shop. From my understanding and what I have read I want to run 6awg thhn/thwn from a 70 amp breaker in my main panel through conduit in my attic and walls to an a/c disconnect style box out side. were I would run through conduit 18 inches under ground to my sub panel. Now, were I am getting confused is since the two structures do not share and common ground (no plumbing or anything) can install a grounding rod at my shed and bridge the neutral and ground bars just like my main panel? There will not be a neutral or ground ran from the main panel. As for the installation how should I secure the conduit in my attic and at what spacing? Also, since both lines leaving the panel will be hot is it acceptable for them both to be black like the service line to the main panel? Thank you for taking time to answer my questions.


Last edited by hzhardy; 06-12-2010 at 02:37 PM. Reason: misspelling and grammar
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Old 06-12-2010, 02:42 PM   #2
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sub panel in work shop.


How far to the workshop ?

No AC disconnect required on the outside of the house
Run 4 wires THWN in conduit, 1" works
You are required to run 4 wires under NEC 2008:
Ground is a very good idea as if you have any other connection between the 2 now or in the future its required
Grounding rods at the detached workshop
Grounds & neutrals are kept seperate
Neutral not bonded to the case

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Old 06-12-2010, 03:52 PM   #3
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sub panel in work shop.


Quote:
There will not be a neutral or ground ran from the main panel.
you do not want any 120 volt power?

by "service" I take that as a service panel. I can't remember the code section but pretty sure you have to take a grounded conductor with the hots.

and yes, you must take a ground wire with you.

drive 2 ground rods at least 6 feet from each other (at least the length of the rod apart is better).

conduit generally must be secured at least every 10 feet and within 3 feet of a box. If running on the trusses, I would use 1 hole straps and some wood screws.
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Old 06-13-2010, 06:32 AM   #4
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sub panel in work shop.


Ok, thanks that clears it up for me. I will drop the service down to 60A run 6-3nm to a AC quick disconnect for extra safety (I do alot of welding and would feel more comfortable knowing I would only need to go a few paces to the house to secure the power in case of fire). then from the box I will run 6awg thwn through conduit under ground. The distance from my main panel is about 75ft. Will the distance result in a substantial drop?
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Old 06-13-2010, 09:20 AM   #5
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sub panel in work shop.


#6 wire at 75' is fine
Voltage drop = ~1.8% ~4.3v @240v
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