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Old 06-05-2010, 02:08 PM   #1
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Wiring a sub panel using 10/2 feeder


I am trying to install outlets and lights in my shed. I ran 10/2 with the intention of having a single branch circuit. After initial inspection, I was told I needed to install disconnect, sub panel, and grounding system. I stopped by an electrical supplier to see if I could do this without replacing the 10/2 with 10/3 and this was their suggestion:

Install 30 amp double pole in basement sub panel using the black and white wires as the two hots. Connect those to another 30 amp double pole breaker in the shed sub panel and then jump them to the two hot bus bars in the sub panel. This will leave no neutral between the two sub panels, is this going to be a problem? Do I float the neutral bus bar in the shed sub panel? Will two 8 ft grounding rods connected by #6 copper wire to the shed grounding bar be sufficient for a grounding system? Are the white wires in the shed circuits connected to the neutral or ground bar in the shed sub panel?

I really do not want to dig up the 10/2 and replace it with 10/3 but I would like to complete this project without violating any codes.

Thanks to all who help with these answers.

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Old 06-05-2010, 02:22 PM   #2
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Wiring a sub panel using 10/2 feeder


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Originally Posted by Willing2learn View Post
I am trying to install outlets and lights in my shed. I ran 10/2 with the intention of having a single branch circuit. After initial inspection, I was told I needed to install disconnect, sub panel, and grounding system. I stopped by an electrical supplier to see if I could do this without replacing the 10/2 with 10/3 and this was their suggestion:

Install 30 amp double pole in basement sub panel using the black and white wires as the two hots. Connect those to another 30 amp double pole breaker in the shed sub panel and then jump them to the two hot bus bars in the sub panel. This will leave no neutral between the two sub panels, is this going to be a problem? Do I float the neutral bus bar in the shed sub panel? Will two 8 ft grounding rods connected by #6 copper wire to the shed grounding bar be sufficient for a grounding system? Are the white wires in the shed circuits connected to the neutral or ground bar in the shed sub panel?

I really do not want to dig up the 10/2 and replace it with 10/3 but I would like to complete this project without violating any codes.

Thanks to all who help with these answers.
Where are you located? What you were told at the electrical supplier was garbage. You must have separate neutral and equipment ground to a detached structure sub-panel.

Also, the 10/2 should have been fine for a single branch circuit, provided that it was protected with no higher than a 20-amp breaker, if you are using it for lights and receptacles. And here in Minnesota at least, you may use a standard 20-amp light switch as main disconnect for a single circuit like that, as long as you label it.

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Old 06-05-2010, 02:27 PM   #3
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Wiring a sub panel using 10/2 feeder


I am in Virginia. I was going out of a diy book and never intended on having multiple circuits or 220V at the shed. However, after the inspection, I lost total confidence in the book I was using and am now trying to figure out a way to wire this shed up without digging up the trench and running new wire (10/3). I was only planning on having a 20 amp circuit at the shed but used 10 gauge to avoid any voltage drop that might incur.
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Old 06-05-2010, 02:33 PM   #4
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Wiring a sub panel using 10/2 feeder


I'm not sure about any local amendments Virginia might have, but according to the 2008 NEC, you should certainly be able to run 10/2 from a 20-Amp breaker in the house, to a 20-Amp switch in the shed clearly labeled "Main Disconnect", and from there to whatever other loads you intend to install out there. And of course all receptacles out in the shed need to be GFCI protected.

You might want to ask the inspector for a specific code reference, it could very well be a local thing.

And the 10/2 cable is type UF, right?
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Old 06-05-2010, 03:01 PM   #5
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Wiring a sub panel using 10/2 feeder


What is the distance to the shed ?
How was the wire run ? Buried...conduit...?
What type of 10-2 wire ?
Where does the 10-2 terminate in the shed ?

Under NEC
Single circuit 10-2 to provide one circuit is allowed
ONLY 1 circuit is allowed to detached structure
OR a MWBC to provide 2 circuits

Disconnect would be a 20a switch

What are you trying to power in the shed ?
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Old 06-05-2010, 03:40 PM   #6
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Wiring a sub panel using 10/2 feeder


Thanks for the help thus far guys, I really appreciate you taking the time to help me with my problem!

To answer some of the questions you guys asked:

1) It is 10/2 UF cable ran through PVC conduit into the trench until the trench depth reaches 24 inches on both sides (shed and house) of the run. Once the trench is at least 24 inches, I ran the wire with no conduit (buried).

2) The distance from the sub panel in the basement is approximately 80 - 85ft, with the buried portion being approximately 65 feet.

3) I have not yet terminated either side of the 10/2 cable. I was planning on terminating both black and white (used as a hot) in 30amp double pole breakers at the sub panel in the basement feeding the sub panel in the shed. From the 30 Amp breaker in the sub panel, I would jump both poles up to the hot bus bars. I have a 100Amp Cutler-Hammer BR series panel that I was going to try to use. With this configuration, I will not have a neutral from my basement sub panel to my shed sub panel. Which is why I am wondering if the sub panel in the shed would act like a main panel and have the neutral and ground bars connected? I have also been instructed to install two 8 ft grounding rods at least 6 feet apart using #6 copper wire.

If I knew in the first place I was going to have to put in the disconnect, sub panel, grounding system in the shed, I would have ran the 10/3 cable and been done with the project.

I would like to try to complete this without removing the 10/2 cable if at all possible. I know this is not a normal configuration so outside the box thinking is necessary, which is why I am on this forum looking for help from people who know what they are talking about.
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Old 06-05-2010, 03:53 PM   #7
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Wiring a sub panel using 10/2 feeder


You absolutely CAN NOT hook this up without a neutral, unless you are running only 240V loads at the shed. If you must put in a sub panel, and don't want to replace the cable, there is only one thing you can do:

At the house panel, connect the neutral to the neutral bar, the ground to the ground bar, and the hot to a single pole 30A breaker.

At the shed, install a main breaker panel with separate neutral and ground bars. Connect the neutral to the neutral bar, the ground to the ground bar. Then, you can either connect the hot to one side of the main breaker, and only have power to every other breaker slot in the panel. Or you can pigtail the hot to both sides of the main breaker, and have power on all breaker slots, but no 240V capability.

You would also need to drive two ground rods at least 6' apart, and connect them to the sub-panel's ground bar with a continuous piece of #6 solid copper.


Think about it for a minute. In a residential split-phase electrical system, you get 120v hot to neutral, 240v hot to hot. If you didn't have a neutral, where would you get your 120v? If you illegally connected the neutral and ground bars in your sub-panel as you mentioned, current would return to the main panel's neutral via the bare ground wire in your 10/2. Essentially using the bare ground as a neutral. This is very illegal, and very dangerous. Every grounded metal part of your electrical system, and any grounded metal tools and etc. plugged into your outlets, would now be part of the return path and carrying current.

I really don't mean to bust your chops, so I'm sorry if this comes off that way, but you really need to do this right.

However, I have heard that most inspectors will not approve either of those configurations. It's kind of hackish and could confuse people down the road.
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Old 06-05-2010, 04:46 PM   #8
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Wiring a sub panel using 10/2 feeder


Yeah, you can't supply 240v (sub) to a detached structure without a 4 wire feed & ground rods

So you need to either supply one circuit or run new wire for a sub
I'm not sure of an Inspector will approve a 120v sub-panel
Or if they will approve a 30a single circuit that then splits to other circuits

Neutrals & grounds MUST be on seperate bars on a sub
Neutral not grounded to case/rods or grounds at all

You need to decide between one 20a circuit (Max allowed as far as I know) or a 4 wire sub panel feed w/ground rods

Is the Inspector forcing you to run a sub-panel ?
You say you planned on terminating with a 30a 240v breaker & sub
Which is it...you planned on a single circuit..or a sub ?
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Old 06-05-2010, 05:42 PM   #9
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Wiring a sub panel using 10/2 feeder


In your second posting you said you don't need 220 in the shed so why would you be connecting both the black and white wires to a two pole breaker? What exactly do you need for outlets and lights in this shed?
Is this something like what you need?
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Old 06-05-2010, 08:03 PM   #10
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Wiring a sub panel using 10/2 feeder


a7ecorsair,

That is exactly the picture that I was going off in my book. I never intended on putting 220V and so I was going to tie into a 20amp single pole breaker in my basement sub panel using the 10/2 to minimize voltage drop. I installed a 20Amp GFCI that was going to start the ciruit and then follow that with a couple of receptacles, an inside switched light, and an outside motion detector light. Intent was to charge a few things and have lights out at the shed, I never planned on needing 220V or a 30 amp circuit out at the shed.

McSteve,

Thanks for the detailed information. I definitely did not want to hear that answer but if that is the right answer, I needed to hear that. I may see if I can go with your option of only feeding one hot in the shed's main panel.

Scuba_Dave,

Thanks for your help as well. To answer your questions, I started out with the intention of running a single circuit but then changed the plan as the inspector said I failed because I needed a disconnect, sub panel and grounding system.


If I am able to leave this as a single 20 amp circuit, how do i tie the 10/2 to the 12/2? Can I use wire nuts or are there rules on this as well?

Final thought, before I start any new projects I will consult with this style of chatroom before any sweat is put into the project.
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Old 06-05-2010, 08:12 PM   #11
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Wiring a sub panel using 10/2 feeder


Single circuit is allowed by code - MWBC is considered a single circuit
GFCI protected before it goes into the trench 12" deep is enough
Run 10-2 to a quad box at switch height
Pigtail #10 to #12 -unless a switch will take #10 ??
Wire nuts rated for the wires are OK

Use a switch rated at 20a as the 1st connection
That is your disconnect
I'd put a switch in the quad box & an outlet
Then run other power from the quad box

If your Inspector insists on a sub ask him for a code reference
I'm looking for a code reference
225.30 is a start
250.32 - no ground rod required for single circuit
There are TONs of sheds (millions probably) & small buildings with only one circuit that meet code

Sub is not required, no sub - no grounding rods
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Old 06-06-2010, 07:36 AM   #12
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Wiring a sub panel using 10/2 feeder


Scuba_Dave,

Thanks again! Is there a place on the Internet where I can find these codes? I was going to buy an NEC 2008 book but it was rather expensive considering the frequency I do any electrical work.
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Old 06-06-2010, 08:01 AM   #13
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Wiring a sub panel using 10/2 feeder


Here are some references - note the EXC
The first entry says an GES (Grounding Electrode System) in not needed if there is a EGC (Equipment Grounding Conductor)
The third box says a disconnect is needed
Fourth entry says a snap switch is OK

So it looks like the Complete Wiring Book has a error - no disconnect
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Old 06-06-2010, 09:34 AM   #14
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Wiring a sub panel using 10/2 feeder


There have been changes under 2008
3 wire feed no longer accepted as far as I know

NEC 2008 link is in my signature
But unless you know where to look you can spend hours reading
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Old 06-06-2010, 10:17 AM   #15
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Wiring a sub panel using 10/2 feeder


Don't use the 10/2 UF cable for a feeder. Use it for a single branch circuit. Then all you need is a simple light switch for the disconnect that is required.
No panel, unless you want to dig up the cable you installed.

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