Bringing 240v 60amp Power to a remote back yard Workshop

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  #1  
Old 05-31-13, 01:08 PM
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Question Bringing 240v 60amp Power to a remote back yard Workshop

Hello again. You all helped me here before: http://www.doityourself.com/forum/el...ack-porch.html

I have reviewed my own thread there, in hopes to help my brother-in-law/friend bring 240v 60amp power to his newly erected back yard shed/workshop of 12' x 16'. His current requirements are small:
4 qty 120v outlets
2 overhead lights
1 dedicated outlet perhaps for a window unit a/c

I have talked to him and stated what I've learned, in that doing this stuff you want to build it with expansion in mind, IE: running outside back yard equipment off the shed power, surge of running power tools like saws, compressors etc.. or who knows later on, back yard lighting.. building a time machine.. etc.. lol.

If he remains with only the need for 120v, then I guess we could go with a 30A subpanel with lesser gauge wiring??? I recommended 60a 240v though because you can do whatever you need with that volume of power once its properly run to the workshop.

The workshop is approximately 60-70ft from the main principal in the house and its power will stem from there.

I have recommended for the 60a 240v subpanel to have 6/3g NM or Romex inside the house/workshop and 6/3g THWN or THHN/THWN type cable outside stemming from junction box in attic all the way down through 1" PVC schedule 40 conduit to the workshop grounding outside in a new grounding rod at the workshop and NOT grounding to the house main principal ground circuit and all of it buried 18" deep (12" for 120v).

I would figure to run THWN or THHN/THWN cable entirely all the way from the main principal of the house through to the subpanel inside the workshop, but the only limitation there is cost right???

Have I missed anything? Does there need to be a disconnect sub panel anywhere else in this or is it ok just to have the one in the workshop alone?
 
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  #2  
Old 05-31-13, 09:02 PM
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You have "missed" quite a bit I'm sorry to say.

First of all, THHN, THWN and the rest of your alphabet soup are insulation types, not cables. Generally when these insulation types are designated they are for individual conductors. A cable is an assembly of two or more conductors with an overall covering. Cable is rarely used in conduit with the exception of short lengths of conduit used for physical protection.

Schedule 40 PVC should not be used at ground level as it is "subject to damage" by the use of mowers and especially string trimmers. At this point only schedule 80 PVC should be used or a metallic conduit such as IMC (intermediate) or RMC (rigid) threaded conduit. Do NOT use EMT (electrical metallic tubing) in this location.

You DO need to connect the equipment grounding conductor to the service panel neutral/ground bus as well as the neutral conductor. At the sub-panel you MUST separate the equipment grounding conductor and attach it to a bonded equipment grounding bus whereas the neutral conductor will attach to the isolated neutral bus. The equipment grounding bus must also be connected to a grounding electrode (ground rod) with no less than #6 copper wire.

Minimum burial depth is 18 inches in most cases although some areas require a minimum of 24 inches. !2 inch depth can ONLY be used with circuits that are GFCI protected at the source AND of 20 amperes or less Ampacity.

The sub-panel DOES require a disconnecting means if it has the ability to serve more than six circuits.
 
  #3  
Old 05-31-13, 09:48 PM
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Schedule 40 PVC should not be used at ground level as it is "subject to damage" by the use of mowers and especially string trimmers.
My Goodness, can a string trimmer cut sch 40? I just wasted many hours with a hacksaw and pipe vise. I had a string trimmer right next to me the whole time! Argh. It turned out just as badly.

Isn't schedule 80 the same stuff, only thicker? So wouldn't the sting trimmer work just as well if the operator held it in place for longer?

The sub-panel DOES require a disconnecting means if it has the ability to serve more than six circuits
Not the "ability to serve", I belive it's more like more than 6 breaker handles / disconnecting means, more or less.
 
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Old 06-01-13, 12:03 AM
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I admit that the phrase "subject to damage" is subjective and open to interpretation. I also know that a string trimmer CAN shatter schedule 40 PVC under the right (wrong) circumstances as I have seen it. Yes, schedule 80 is the same stuff but with thicker walls than schedule 40 but it seems to be much more resistant to cracking or shattering under stress. My point is not that a string trimmer can, or can't cut PVC conduit if held in position long enough but that ACCIDENTAL damage to schedule 40 PVC is much more likely than it is with schedule 80 PVC.

I meant exactly what I stated. For an example consider a panel that takes six, single pole, full-size circuit breakers OR six, twin circuit breakers. The panel has six full size slots but could, with the use of twin circuit breakers serve twelve separate circuits. The NEC is clear that six or fewer circuits does not require a main circuit breaker or single disconnect. By interpretation that means that any more than six DOES require either a main circuit breaker or disconnect. Installing the six full size single pole circuit breakers in this panel would meet the requirement of no more than six but if the panel is listed for use with the twin circuit breakers then someone could after the initial installation replace one, or all, of the original circuit breakers with twin models and thereby be in violation. For that reason the requirement is that IF the panel can accept more than six circuits, regardless of how many are installed, it MUST have either a main circuit breaker OR a separate disconnect when the panel is located in a separate building from the Service panel.
 
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Old 06-01-13, 01:08 AM
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Furd-That's an interesting point about what the next guy might do, but isn't that reaching a bit?

And If you have a backfed "main" breaker in the panel, think about how that affects things. You're liable to go nuts thinking about the circular argument. Maybe it's too late??? (awww ok seriously I'll ponder this and argue back)
 
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Old 06-01-13, 03:41 AM
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I believe a 30 amp feeder would be more than enough based on the description of the intended usage. An oversized conduit could be installed to futureproof.

The 30 amp panel would still supply 240 volts from the 4 wire feeder.
 
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Old 06-01-13, 02:17 PM
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Furd-That's an interesting point about what the next guy might do, but isn't that reaching a bit?
Not at all. In fact, most inspectors will not pass an installation on this very point.
 
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Old 06-03-13, 11:56 AM
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It all depends on what town you are in, how the inspector is feeling that day and what time of day you get him/her. lol - Just a lil joke Furd.

Furd - I appreciate your dissecting of my word salad or ... as you put it... alphabet soup. I think expressing the differences in terminology is key to communication, but where I'm from wire, cable, run are used synonymously in slang, though its probably better, I'd bet you'd agree, to leave slang out of electrical work huh?

pcboss - So for a 30amp run 4 wire feeder of 240v what wire/insulation type should we go with inside the conduit? 12/3 ?? Think we should just do 120v ?

Big bang theory anyone?
 
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Old 06-03-13, 12:16 PM
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You really have only two choices. You can run type UF (underground feeder) cable with three insulated conductors and a bare equipment grounding conductor OR you can run individual conductors with type THWN insulation in conduit. The term 12/3 indicates a cable and individual conductors are never designated this way.

Pulling type UF cable through conduit is difficult under the best of conditions and working with UF is just plain hard in my opinion. I would strongly suggest that you use a complete conduit run and use individual conductors. Most of the individual conductors readily available will have multiple ratings and seeing THHN/THWN printed on the insulation is common and denotes the wire is suitable for wet locations. ALL underground conduits are considered wet locations.

Wire sizes vary according to the Ampacity which is a technical term meaning the maximum amperage that is allowed to flow through the wire. For 30 amperes you need to use a minimum of #10 AWG wire.

I strongly suggest that you buy the book Wiring Simplified and read it cover-to-cover. Wiring Simplified has been in continuous print for more than fifty years and is updated every three years to follow the updates to the National Electrical Code. It is written for the layman and tells you not only the way things are done but also tells you WHY they are done in the particular manner. The cost is less than $10 ($6.95 at HD in my area last I looked) and it is found in the electrical aisle of most big-box mega-mart homecenters. It usually is not found in the books and magazine area.
 
  #10  
Old 06-04-13, 12:04 AM
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Thanks Furd and all.

So, if we want 240v we'd run 2 hot #10 AWG wire of THHN/THWN, 1 for neutral and 1 for ground and that would give us a 240v 30amp subpanel??

I will get the book, but a book is never as good as this forum or forums of the like.
 
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Old 06-04-13, 01:05 PM
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I will get the book, but a book is never as good as this forum or forums of the like.
Thank you, but do buy and read the book. Some of us refer to Wiring Simplified as "the text for our online seminar."
 
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Old 06-04-13, 02:09 PM
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"Wiring Simplified" is the book that got me started in the electrical trade. It is cheap, and an interesting read.

I would go either with the 30 amp 240 volt circuit, or a 60 amp 240 volt circuit, whatever his budget allows, and what his future plans might be. I would surely install a small panel (12-20 spaces) in the shed for the availability of adding circuits. IF you want, you could just pull in #10 wire for a 30 amp circuit, but install 1 1/4" PVC conduit. That will give him the room to add larger wire down the line if needed. And since you have a trench open, he might want to add a communication conduit for TV, Phone and Network.

Doing a 120 volt circuit only is a waste of time in my opinion.
 
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