Re-wiring a shed?

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  #1  
Old 12-05-13, 06:27 PM
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Re-wiring a shed?

I have a shed that I think has outgrown its current wiring. The wire running to the shed was tapped into a light in the crawlspace which is on the same 15amp breaker as our den. I'm assuming the wire is 14/2. The wire runs underground from the crawlspace to a GFCI receptacle on the outside of the shed. The shed has 4 outlets inside (14/2 wire) and an overhead light. My tool collection has grown since I initially added the interior outlets (the GFCI was already there when I bought the house) and after purchasing a 15 amp miter saw, the light now goes off when the saw is in use. I plan on adding a table saw as well, so I need to get the wiring fixed beforehand. The shed is roughly 50-75ft from the main panel.

So if I add a 20 amp breaker to the main panel, run 12/2 UF wire straight from the panel to the GFCI outlet on the shed, and change the wiring inside to 12/2 as well, will that be sufficient? Any need for a sub panel at the shed? Any need to bump it up to 30 amp and 10/2?
Thanks
 
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  #2  
Old 12-05-13, 07:01 PM
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I'd suggest 12-3 instead on either a 240v breaker or two handle tied single pole breakers. That will give you two 20 amp 120 volt circuit and all you will need is a 2-pole switch or disconnect.
 
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Old 12-05-13, 07:01 PM
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Welcome to the forums!

If you're the only one who'll be working there you might get away with a 20A MWBC, but I'd go with 30A to be on the safe side and future-proof the installation. Either way will save you the cost and hassle of putting in a subpanel.

Ray explained sow to do the 20A MWBC. It's simpler and less expensive, and may be all you need.

To run 30A, you'll need two 30A breakers joined with a handle tie and #10 wiring - two hots, a neutral and a ground. In the shed, you'll need a small load center with maybe four breakers in it. You'll need a disconnect for the power - a 2-pole safety switch or a main breaker in the load center. Your jurisdiction may or may not require it, but I'd drive one or two ground rods and tie them into the load center. Keep the grounds bonded and the neutrals isolated.

Unless the table saw needs more than 15A, you could get away with 14-2/G Type NM (Romex) off 15A breakers for everything inside the shed. 20A breakers and #12 wire are generally preferable for receptacles though, IMX.
 
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Old 12-05-13, 07:03 PM
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A better solution might be a 30 or 40 amp subpanel. A 20 amp circuit will not give you a whole lot more than what you currently have. You could run a multiwire branch circuit that will give you options.
 
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Old 12-05-13, 07:05 PM
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Geeze we have an echo in here. LOL!!
 
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Old 12-05-13, 07:06 PM
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There is a terrible echo on here tonight with a 2 minute delay. Grin
 
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Old 12-05-13, 07:07 PM
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Geeze we have an echo in here. LOL!!
Ow!! My ears!!!..........................
 
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Old 12-05-13, 07:16 PM
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It's definitely something else. Echoes don't travel that fast.

I would go with 8-3 wire (40 amps @ 240 olts) for futureproofing. If you use 20 amp breakers back at the main house panel then you would not need a subpanel (load center) or ground rods out at the shed yet.
 
  #9  
Old 12-05-13, 09:15 PM
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I'm a little confused on the multiwire circuit? If I put in a two pole 20 amp breaker and run 240 to the shed would I run both hots to the one GFCI receptacle (one to the top outlet and one to the bottom)? But then I wouldn't be able to feed the other outlets down the line? Or would I need to install another GFCI outlet for the second hot?
 
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Old 12-05-13, 09:39 PM
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120 volts is derived from one hot and a neutral. In a multiwire circuit you have a shared neutral and two hots. Therefore you can derive two circuits using the two hots and the shared neutral. You can share the neutral because it only carries the difference between the amps on the two hots.

One typical way to wire this is use a cheap unfused 60 amp pull out air conditioner disconnect at the entry point to the shed. While it is overkill amp wise it provides both a large junction box and code required disconnect in one package at a low price. At the disconnect two 12-2 cables are connected to the feed. All whites are wire nutted together. Red and black of the feed go to the input (line)of the disconnect. The black of one 12-2 goes to one side of the output (Load) and the black of the other 12-2 goes to the other side. The first receptacle on each 12-2 must be a GFCI. (Lighting should be before any GFCI (or branch off the line side of the GFCI) so you aren't left in the dark if a GFCI should trip.)

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Last edited by ray2047; 12-05-13 at 10:08 PM.
  #11  
Old 12-05-13, 09:58 PM
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I'm a little confused on the multiwire circuit? If I put in a two pole 20 amp breaker and run 240 to the shed
You shouldn't use a 2-pole breaker. You should use two single-pole breakers with their handles joined by a handle tie. You're also not running plain 240V, which doesn't use a neutral. You're running two 120V circuits that share one neutral. The handle tie allows each to trip independently of the other but requires that both be turned off before doing any work on the wiring.

Yes, you can use this wiring to feed a 240V appliance, by ignoring the neutral. You wouldn't have a lot of capacity left for any other use though.

would I run both hots to the one GFCI receptacle (one to the top outlet and one to the bottom)? But then I wouldn't be able to feed the other outlets down the line? Or would I need to install another GFCI outlet for the second hot?
You're right. One hot/neutral 120V pair of wires is connected to the LINE terminals to feed the receptacle. The pair(s) of wires feeding out to other loads to be protected are connected to the LOAD terminals.
 
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Old 12-05-13, 10:13 PM
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And while Nash is correct that two single pole breakers are used it is not a code violation to use a 2-pole breaker. A 2-pole breaker may be the only alternative if you can't find a single pole breaker dual rated 120/240 or a manufacturer approved handle tie but that isn't likely to be the case.
 
  #13  
Old 12-06-13, 06:42 AM
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You can connect any number of ground fault circuit interrupter receptacle units to the incoming multiwire branch circuit. For each GFCI unit, connect either the red and white of the feed or the black and white of the feed to the GFCI unit Line terminals.

For most purposes you need a maximum of two GFCI units, one connected to the red and white and the other connected to the black and white. Use additional 2 conductor (plus ground) cable (not part of the MWBC) to connect the load terminals of a GFCI unit to additional plain receptacles.

Do not connect the neutral (or hot) of the MWBC (here, the incoming feed) to the load terminals of any GFCI receptacle.
 
  #14  
Old 12-06-13, 08:31 AM
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Thanks, the diagram really helped! So would you recommend having one 12\2 dedicated to the outlet that is going to be used for the miter saw/table saw, and use the other for the other outlets/light? Or does it not really matter?
 
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Old 12-06-13, 09:07 AM
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while Nash is correct that two single pole breakers are used it is not a code violation to use a 2-pole breaker.
Ray is correct. Technically, either can be used.

I only use and recommend using two single-pole breakers joined with a handle tie to supply and protect the two hots in a MWBC because only by doing that can you allow each circuit to trip on its own while still having to turn them both off to do any work.

The NEC requires both "common disconnect" and "common trip" for 240V circuits. It only requires "common disconnect" for MWBCs, and I think it's written that way for a reason. But it is my opinion, not a regulation.
 
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Old 12-06-13, 09:35 AM
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I'd put usually not used and low amp use receptacles on the light circuit and high amp use circuits on the other but that is personal opinion. You may also want to consider using a 10-3 or the 10-8 feed that Allan suggested so if you need more load or 240v you can just swap out to a larger breaker and
change to a subpanel in the future.
 
  #17  
Old 12-06-13, 12:56 PM
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I just noticed that the current wire going to the shed from the light in the crawlspace is 10/2. Would tapping into this wire with another length of 10/2 from the new 20 amp breaker at the panel fix the issue? This would be much easier than digging up and rewiring the current setup!

I'm already running out of space in the shed so the table saw is going to be the last big thing I add. So, I don't think I need to worry about futureproofing too much.
 
  #18  
Old 12-06-13, 01:45 PM
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I just noticed that the current wire going to the shed from the light in the crawlspace is 10/2. Would tapping into this wire with another length of 10/2 from the new 20 amp breaker at the panel fix the issue? This would be much easier than digging up and rewiring the current setup!
No. You would need 10-3 UF cable. You need two hot (blk & red) and a neutral (white) plus the ground wire.
 
  #19  
Old 12-06-13, 02:00 PM
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I was wondering if that would work instead of the multiwire circuit? Everything would be wired up the same as it is now (one GFCI), except it would be running off it's own 20amp breaker from the panel. I understand that the multiwire circuit is better and would give me more options, but was courius if this may fix it as well?
 
  #20  
Old 12-06-13, 02:00 PM
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Just to add (pun slightly) intended. You can't add a second source of power to the shed. National code prohibits two circuits to a detached building. (Multiwire counts as one.) in fact you will be required to abandon your current feed when you run the new one.

The 10-2 you have could be connected to a 30 amp breaker and used for a 120v only subpanel.
 

Last edited by ray2047; 12-06-13 at 02:22 PM.
  #21  
Old 12-06-13, 02:12 PM
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Just to add (pun slightly) intended. You can't add a second source of power to the shed. National code prohibits two circuits to a detached building. (Multiwire counts as one.) in fact you will be required to abandon your current feed when you run the new one.
The way it is wired now the 10/2 goes from the light (which is off a 15amp breaker) in the crawlspace to the GFCI at the shed. Instead of doing a multiwire circuit, could I run 10/2 from a new 20 amp breaker at the panel and connect it to the old 10/2 (after disconnecting it from the 15amp circuit of course). There would still be only one circuit running to the shed. Everything would be the same as it is now, it would just now have it's own 20amp breaker instead of the shared 15?
 

Last edited by ray2047; 12-06-13 at 02:16 PM. Reason: Correct typo in my quote.
  #22  
Old 12-06-13, 02:20 PM
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could I run 10/2 from a new 20 amp breaker at the panel and connect it to the old 10/2 (after disconnecting it from the 15amp circuit of course). There would still be only one circuit running to the shed. Everything would be the same as it is now, it would just now have it's own 20amp breaker instead of the shared 15?
Yes that would work though as I wrote I'd use a 30 amp breaker and install a 120 subpanel at the shed. Your way would be the easiest/cheapest and increase the power available to the shed.
 
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