Go Back  DoItYourself.com Community Forums > Electrical, AC & DC. Electronic Equipment and Computers > Electrical - AC & DC
Reload this Page >

Multiwire or subpanel a new shed and other shed wiring Q's

Multiwire or subpanel a new shed and other shed wiring Q's


Old 01-16-14, 02:45 PM
Thread Starter
Join Date: Jan 2014
Posts: 5
Multiwire or subpanel a new shed and other shed wiring Q's

I am building a detached shed in my yard and would like to run power to it. The shed will be under 200 ft^2, nothing special wood frame on the floating dek-block foundation. I know my way around construction in both mechanical and electrical from growing up in a builder family. But it was mostly commercial so I know enough to be dangerous

Load: lights and 1 receptacle. Lighting would be a fluorescent inside, and a ~100W yard light. Receptacle would be running xmas lights/party lights most of the time. The largest load I can foresee is my 15A circular saw. This is a storage shed and no shop. So I don't have my whole assortment of power tools running off of this. I also don't see any chance of the load expanding in the future. Therefore 20A to the shed seems to be ample. Agreed, or am I over killing this and unnecessarily adding to my wire gauge?

Total run is 50ft. ~30 through house walls and crawl space, followed by ~20ft of underground though conduit. Yes my service panel is at the opposite end of the house to the shed location, but at least I have crawl space where I actually fit.

My questions:
  • Am I best served with a multiwire to the shed or subpanel?
  • What gauge would work for this and do I need to run romex from the service panel to conduit, then switch to stranded wire? I assumed 10-3 copper is best.
  • I have a poured foundation wall with wood frame on top for my house. Do I need to punch a hole for the conduit through the foundation below grade or can I go through the exterior wall above the sill plate to a LB then into the ground?
  • Is there any guidance/code on how I need to bring the conduit up into the shed since it is on the dek-blocks? BTW the shed will be on level ground so there is no space for a kid to crawl or a mower deck to slide under and snag a line.
  • RMC or PVC conduit? what diameter?
  • Do I need a GFI at my service panel?

I'll likely have more Q's later, but this will get you all started!
Sponsored Links
Old 01-16-14, 03:07 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 33,054
Use 1" conduit to future proof and for now run four #12 for a multi wire circuit on a 20 amp breaker. Further future proofing would be four #10 instead of #12 but still on a 20 amp breaker so at a later date you could add a subpanel and change the breaker to 30 amp.

RMC is harder to work with then PVC and PVC is fine for this. Make the first receptacle on each circuit rather then a GFCI breaker for cost and so you don't loose lights if there is a trip. Only advantage in using a GFCI breaker is burial depth.
Old 01-16-14, 03:11 PM
Join Date: Mar 2010
Location: USA
Posts: 3,098
You could have conduit exiting the house above ground just above the sill plate to avoid boring through the concrete foundation, then a pull box elbow just outisde, then it dives down below ground. Use wet rated single conductors (THWN) rather than direct burial Romex if using conduit underground.

If you decide to future proof anyway, I would use 8 gauge (with 10 gauge ground) (40 amps) rather than 10 throughout.

Last edited by AllanJ; 01-16-14 at 04:00 PM.
Old 01-16-14, 04:28 PM
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,399
If you are sure that you will never want to increase the load I would suggest all #12 wire and a multi-wire branch circuit. You can avoid the conduit underground by using type UF cable. Use an LB fitting at both the house and the shed and if you use PVC conduit use schedule 80 where it enters/leaves the ground or else use IMC (intermediate metal conduit) in these places for protection against lawnmowers and string trimmers.
Old 01-17-14, 12:17 AM
Thread Starter
Join Date: Jan 2014
Posts: 5
Thank you Ray, you just saved me a fortune in breakers.

Allan, I think I'll run UF instead of a conduit underground. That saves me from having to run conduit to the service panel or having a thwn to romex connection somewhere in my crawlspace.

Furd, PVC vs IMC will probably boil down to cost for me at the moment. UF #12 sounds like it will be plenty for what I need in this application, unless I find #10 on sale.

Thanks for all the helps guys!

Do I need a ground rod at the shed?
Where the UF enters and exits the conduit in the dirt, do I need a cable clamp there or pack it with caulking?
Old 01-17-14, 12:47 AM
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,399
You need conduit from the point of exit at the house and to the point of entrance at the shed. This conduit should extend underground to eighteen inches minimum and then bend in the direction of the run. Using type UF cable the conduit serves only to mechanically protect the cable and no clamp or sealing of the conduit end underground is necessary. This conduit should be schedule 80 PVC or IMC for protection from damage. IMC is significantly less expensive than RMC although also more expensive than PVC. Not all big-box mega-mart homecenters carry schedule 80 PVC and some may carry IMC but not RMC and vice versa.

If you run a multi-wire branch circuit you do not need to install a grounding electrode (ground rod) but if you install a feeder circuit to a sub-panel then you DO need at least one grounding electrode. In either case you need a means to disconnect all ungrounded (meaning the two "hot" conductors in a multi-wire circuit) at the shed. The simplest and least expensive is usually an unfused air conditioning disconnect.
Old 01-17-14, 01:27 AM
Join Date: Oct 2013
Location: United States
Posts: 235
Storage Shed

As mentioned all your receptacles are required to be GFCI protected. You will also need to decide on what method you will use for a disconnect. If you run a multi-wire branch circuit (considered a single circuit by code) you can use single-switches as the disconnects, one for the lights and one for the receptacles.
225.30, 225.33(B),225.39(A) 2008 NEC. We are still on the 2008 code here. Where you install a single circuit, including a multi-wire branch circuit to your shed 250.32(A) Exception allows you to NOT install a ground rod by using the ground that is run with the circuit to be the grounding method.
Old 01-17-14, 01:29 PM
Thread Starter
Join Date: Jan 2014
Posts: 5
Thanks for the details.
I have Platt supply down the road that will have Sch 80.
I think I will replace the LB on the shed with the AC disconnect instead of using the switches for disconnects.
Thanks for everything guys!

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes