Detached Shed Voltage Drop

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Old 03-28-16, 04:54 PM
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Question Detached Shed Voltage Drop

I purchased this home in December 2015 in Charlotte, NC and I'm having trouble with the power out to the shed.

My shed is wired with two outlets and two light fixtures (60w bulbs). I recently decided that it would make a good workshop for small woodworking projects/ general tinkering where I don't have to worry about burning the house down.

I tried to run my miter saw off of one of the outlets and not knowing at the time how it was wired, I saw the #10 wire and thought I'd be fine running some tools out there from time to time, but 120v drops to 89v when the saw is running.

I tracked the wiring back to the house, where the #10 wire is attached to the screw terminals of an exterior outlet, which has a #14 feeder pushed into the back of it. Great. But thinking about it, I don't understand why the voltage dropped to such an extent. I should be able to have less than a 3% drop since it's under 40' from the panel to the tool (I used an online voltage drop calculator ). I plan to check the connection at the outlet on the house since it looks suspect, but I didn't see any charring/melting/fire.

How would those of you who are proficient in residential wiring have run this wiring? I would like to eventually be able to run a saw, lights, and maybe a small A/C. I know the #14 wire wouldn't cut it, but could the existing #10 handle a small sub-panel to do what I need?



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Old 03-28-16, 05:04 PM
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Welcome to the forums.

If you had a light bulb and saw plugged in directly to that outside receptacle you'd get the same drop. The drop is thru the #14 in the house. Push-in connections don't help either.

I doubt the #10's can supply you enough power.
How many #10's do you have and what are they.... loose wires in a conduit ?
What size conduit ?
 
  #3  
Old 03-28-16, 05:43 PM
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No way should it just be plugged into an outlet!
Should have been run all the way to the panel box on it's own breaker.
One of my many pet peaves seeing garages and sheds being under wired.
Most people want to cheap out and figure they only need a few outlets and lights which may work fine if you do not plan on running anything but a drill or vacuum cleaner.
Any detached real shed or garage I've ever built that was going to have power had at least a 60 amp. panel and was wired for 240 volts, with 2 grounds at least 6' apart.
 
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Old 03-28-16, 05:54 PM
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No way should it just be plugged into an outlet
Joe it isn't. He meant they back stabbed the receptacle.
Any detached real shed or garage I've ever built that was going to have power had at least a 60 amp. panel
I respectfully disagree. In many cases a single 20 amp circuit or a 20 amp multi wire circuit is enough.

Rusty wrote:
I tracked the wiring back to the house, where the #10 wire is attached to the screw terminals of an exterior outlet, which has a #14 feeder pushed into the back of it.
A chain is only as strong as its weakest link. If you mean the house receptacle is fed by #14 then it doesn't matter if you have #10 to the shed. It is limited by the #14. The back stabs are a secondary factor that affects operation. They often do not make good contact. The third limiting factor is how many and the amps of the other loads on the circuit.
 
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Old 03-28-16, 06:33 PM
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Welcome to the forums.
Thanks! I've been here for a while, lurking in the shadows.

If you had a light bulb and saw plugged in directly to that outside receptacle you'd get the same drop. The drop is thru the #14 in the house. Push-in connections don't help either.
Funny, that's how I noticed it, the lights pretty much turned off when I fired up the saw.

I doubt the #10's can supply you enough power.
How many #10's do you have and what are they.... loose wires in a conduit ?
What size conduit ?
I meant 10AWG wire at the shed (~2x the thickness of 14AWG). The wire is a direct bury rated wire, just in conduit to get it in the ground, then buried in just the sheath.

He meant they back stabbed the receptacle.
Precisely, I guess that was the term I was looking for.

A chain is only as strong as its weakest link. If you mean the house receptacle is fed by #14 then it doesn't matter if you have #10 to the shed. It is limited by the #14. The back stabs are a secondary factor that affects operation. They often do not make good contact. The third limiting factor is how many and the amps of the other loads on the circuit.
I'll swap the back-stabbed wires over to the screw terminals and test. I was just surprised to get a 25%+ drop in voltage when just a #14 wire by itself should be good for 44'@15A.

I plan to run a new circuit eventually, and was hoping to re-use the #10 wire that's already buried (digging hurts). I was wondering what my options are as far as a sub panel and amperage if I were to run #10 the rest of the circuit (from where it comes out of the ground by the house to the main panel).
 
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Old 03-28-16, 06:46 PM
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If it is 10-2 cable you can't for practical purposes install a subpanel. For a subpanel you need at least 10-3, two hots, neutral, ground.
 
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Old 03-28-16, 07:47 PM
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You can have a subpanel with just 10-2, you will only have 120V. Nothing says a subpanel has to be fed with 2 hots for 240V.
 
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Old 03-28-16, 08:01 PM
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You can have a subpanel with just 10-2
What I wrote was:
If it is 10-2 cable you can't for practical purposes install a subpanel.
But it doesn't make that much sense and since 120 volt panels are a specialty item you usually end up using a 240v panel anyway.
 
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Old 03-28-16, 10:40 PM
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I would like to eventually be able to run a saw, lights, and maybe a small A/C.
With 10-2 you would end up with 120v at 30A. Yes you could put a sub panel on that but you still don't have much power there. You will still the lights dim when the saw starts or the A/C is running and the saw starts.
 
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Old 03-29-16, 04:25 AM
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Just a curiosity comment. How did they backstab a #10 into a receptacle?
 
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Old 03-29-16, 06:23 AM
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Did you try running the saw (or a hair dryer) from the receptacle back at the house where the 10-2 cable from the shed was tied in?

I would not expect a voltage drop down to 80 volts even with the existing wiring including the 14 gauge, unless there was a loose connection or deteriorated wiring, possibly underground.

Currently you are limited to 15 amps out in the shed because the circuit where the shed wiring is tied in is a 14 gauge circuit. This should have a 15 amp breaker at the panel in the basement.

You could run a new 10-2 cable from the panel over to where the 10-2 from the garage reaches the house and get 30 amps out to the shed. You must have a subpanel out in the shed before you can up the circuit beyond 20 amps, and the 30 amp circuit may not directly serve receptacles and lights in the house along the way. (It would be better to not share this new circuit with anything in the house anyway regardless of amperage.).

If you did conclude that the underground 10-2 had deteriorated in the middle I would run an 8-3 in its place, all the way to the panel. It can still be energized with a 20 amp breaker set if you don't want to put a subpanel in the shed yet. Major equipment such as an air compressor and sawdust gatherer and electric heat, plus more than one person working at the same time, and you are knocking on the door of 60 amps (a 6-3 cable).
 

Last edited by AllanJ; 03-29-16 at 06:45 AM.
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Old 03-29-16, 06:44 AM
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Wiring

Just a curiosity comment. How did they backstab a #10 into a receptacle?
Larry, I read it to mean the #14 coming out of the house was back-stabbed.
 
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