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Old 03-17-2011, 10:01 AM   #1
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Questions about subpanel in a new shed


I just recently put down a deposit on another shed. I'm planning on installing a subpanel there for electric heat & light for housing small birds (nothing heavy like welders or power tools). I've installed my own branch circuit within the house successfully for a gas hot water heater with a power vent as well as other various small electrical projects around my house, so I'm familiar with the basics. I'm a computer hardware engineer by trade.

I understand I need to use conduit for this type of thing, and I have a few questions about the conductors, breakers, and the conduit:

  1. I've calculated my current needs as 10.1A (including the 25% margin) continuous load for heating etc. plus 6.5A non-continuous. I'm planning to install a 30A two-pole 240V breaker in the main panel. I intend to use 3 #8 conductors and one #10 conductor for the ground (all THHHN/THWN). The larger gauge is mainly because it's going to be about a 125 ft run including an underground section. I've checked this with some calculators on the web and they seem to agree, but I'd like to hear it from a person . Main panel is 200A and has a number of slots open; I had my service upgraded from 100A just a few years ago.
  2. Subpanel in the shed will have 15A two-pole 240V breaker for baseboard heat (1000W), 15A 120V breaker for lighting (250W or so), and 15A 120V breaker for an outlet or two. Sound OK?
  3. I'm going to use 3/4" sch 40 PVC conduit for the run inside the house. I'm a little unsure about how to route the conduit into the main panel in the garage. It's pretty crowded both above & below, so I'd like to come out through one of the knock-outs on the top left side. Although the main panel is surface-mounted, I have bare stud walls in my garage. I'm thinking about mounting a sheet of 1/2" plywood to span the two studs to the left of the panel to get the conduit up to the top plate so I can start running it horizontally to the back wall of my garage. Would this be acceptable? Please see the attached photos. In one of them, I tried to "sketch" in where I was thinking about mounting the plywood and routing the conduit.
  4. Should I use GFCI breakers/outlets anywhere? Are they required in a detached structure like this?
Thank you,
Greg
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Old 03-17-2011, 10:38 AM   #2
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Questions about subpanel in a new shed


No. Don't route the conduit that way. Go up and to the left. This way you only have one 90 degree bend. You are only allowed 360 degrees for a run of conduit before you need a pull box (Jbox). You have plenty room to go up and over. You don't have to go up all the way. Just put a small outward kick in the conduit to bring your 90 flush with the studs. Then you can strap it to the studs. No plywood required.
Also, the exposed NM cables shown above should be sleeved. The NEC prohibits NM cables to be in a position where the can be damaged.

Note: Use the search function above. Its loaded with information on sub panels. Loads of information. Any question you have is answered if you look for it.

Last edited by J. V.; 03-17-2011 at 10:45 AM.
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Old 03-17-2011, 08:52 PM   #3
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Questions about subpanel in a new shed


J.V.,

Thanks for your response. I had hoped there would be a less convoluted way of starting this run from the panel, but I wasn't sure if I was allowed by code to make a turn like that from the side of the panel to the adjacent stud. I think I'll use a flexible elbow to route it from the panel to a point on the side of the stud and go from there unless you or anybody else knows of a reason why this shouldn't be done.

About the NM cable above - do you mean all of it that was shown in the picture or just the two sections coming up that stud and heading off to the left where I'm planning to run the conduit? Is there a way I can sleeve it without having to rip it all down and re-do it?

Thanks for the tip - I have searched these forums and found lots of good information such as the 360 degree rule you mentioned, subpanel information, and the maximum number of conductors allowed in conduit. I just wanted to be sure I interpreted it all correctly.

Thanks again,
Greg
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Old 03-18-2011, 12:34 AM   #4
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Questions about subpanel in a new shed


recommend 1" pvc conduit-easier to pull wire.
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Old 03-18-2011, 10:45 AM   #5
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Questions about subpanel in a new shed


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Originally Posted by gmarena View Post
J.V.,

Thanks for your response. I had hoped there would be a less convoluted way of starting this run from the panel, but I wasn't sure if I was allowed by code to make a turn like that from the side of the panel to the adjacent stud. I think I'll use a flexible elbow to route it from the panel to a point on the side of the stud and go from there unless you or anybody else knows of a reason why this shouldn't be done.

About the NM cable above - do you mean all of it that was shown in the picture or just the two sections coming up that stud and heading off to the left where I'm planning to run the conduit? Is there a way I can sleeve it without having to rip it all down and re-do it?

Thanks for the tip - I have searched these forums and found lots of good information such as the 360 degree rule you mentioned, subpanel information, and the maximum number of conductors allowed in conduit. I just wanted to be sure I interpreted it all correctly.

Thanks again,
Greg
Greg. No flexible 90. Come out of the top of the panel with a short section of conduit. Put a slight bend in it so the 90 will run flush with the studs. We call it a kick. Better than two 90's and professional looking.

The cable situation was mentioned, because its a violation to install NM cable where subject to physical damage. By no means do you have to do anything as "subject to physical damage" could mean anything, but you get the picture and so does the NEC.
However. Since it looks like a mess, why not clean it up and sleeve the cables up close to the ceiling. Any cables that run perpendicular to the studs should be pulled through holes drilled in the studs or behind the studs. They should also be in holes at the top sill. Installed as if you planned to put up drywall for an example. Do you understand?
Just turn off the breaker for the cable. Disconnect the cable from the panel, pull it out, insert a sleeve and reinstall. You will need some conduit, some connectors with lock nuts and some plastic bushings. You want a connector at the top of the sleeve with a bushing. PVC can be used. I like EMT, but it will be harder for you to work with.

The picture on the top is just for general cable routing and the picture on the bottom is showing a sleeve with connector and bushing at the top (yellow). Sorry I could not find something matching your application, but these pictures should make this more clear. I hope?




Don't tell anyone, but you could just ignore the cables. I promise not to tell.
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Old 03-18-2011, 04:43 PM   #6
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why not just install a piece of plywood and now they are protected?
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Old 03-19-2011, 11:50 AM   #7
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why not just install a piece of plywood and now they are protected?
And squash the cables between the plywood and the studs? Those cables need to be in the stud (through bored holes) or behind the studs to install any plywood or wall board of any type.
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