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Old 01-16-2013, 10:22 PM   #1
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Sub Panel over 10g-2 Help Needed


I have a large shed about 50' from the house. It currently has 120v over a 10-2 underground wire via a 20a breaker in the house panel and it is not in a metal conduit. There is not a sub panel in the shed. The lights and outlets are simply tied to the feed. I want to install a sub panel in the shed because I want to get 240v for a window ac w/heat that requires 15a. Plus I am tripping the 20a breaker because I was trying to run lights, a 1500w space heater, 2 400w ceramic radiant wall heaters, and a radio. Proves to be a little much for the circuit.

Here's what I have/need:
Ac/Heat 240v 15a
6 2 bulb t8 fixtures 120v 0.5a each 4a total
8 outlets
2 400w ceramic radiant wall heaters

From what I have been able to figure out so far I should be able to run 240v over the existing 10-2 wire with a 30a double pole breaker in the main panel. I would use the black to one side of the breaker, the white (what would normally be red) on the other side of the breaker, and the bare ground as the neutral. No ground from the main panel to the sub panel. I planned on separating the lights on a 15a breaker (would only be pulling 4-5a), the outlets on a 20a breaker, and installing a 240v 15a outlet off of a dedicated double pole 15a breaker for a total of 3 breakers totaling 65 amps.

I have already installed a double 30a in the main panel and put the black wire one one leg, the white wire on the other, and left the ground wire on the neutral bar. I have hung an Eaton type BR 125a 12 circuit 6 space sub panel in the shed, hooked the black wire to one lug, the white wire to the other lug, and the ground wire to the neutral bar. I installed a single 15a breaker in the sub panel and hooked the light circuit to it. I have NOT installed a ground wire from the sub panel to a grounding rod. But no lights. When I tried to put my meter to one of the lugs, it sparked. Because I am not grounded???

So here's were I am not very clear. The sub panel only has one bar in it. The neutral/ground bar. Can I run all of my neutral and ground wires to this one bar or do I need to install a separate ground bar. Since there is not a ground wire running from the main panel to the sub panel, do I need to install a ground wire from the sub panel to a ground rod or rods?

I hope I explained this through enough. Any help will be greatly appreciated. I will try and get a pic to post.


Last edited by hamblinh; 01-16-2013 at 10:26 PM.
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Old 01-16-2013, 10:34 PM   #2
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Sub Panel over 10g-2 Help Needed


Not legal using a 10-2. You'll either have to set a transformer to create a SDS neutral, or install a new feeder cable.

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Old 01-16-2013, 10:45 PM   #3
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Sub Panel over 10g-2 Help Needed


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Not legal using a 10-2. You'll either have to set a transformer to create a SDS neutral, or install a new feeder cable.
I thought I had read that if the 10-2 was existing prior to the NEC code change, the wire could be used for 240v. Can you explain the transformer setup?

Here's a photo of the sub panel.
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Old 01-16-2013, 10:52 PM   #4
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Sub Panel over 10g-2 Help Needed


Where's your cable clamp for the sub?
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Old 01-16-2013, 10:53 PM   #5
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Not legal using a 10-2. You'll either have to set a transformer to create a SDS neutral, or install a new feeder cable.
I know a subpanel in a separate location must be grounded locally, but does it also have to be grounded to the panel? Isn't there some prohibition against grounding in two places?
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Old 01-16-2013, 10:58 PM   #6
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Where's your cable clamp for the sub?
Are you talking about the clamp to hold the wires were they enter the panel? If so, I plan on going back and adding clamps once I make sure this is going to work. I also planned on stripping back the covering for the wires.
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Old 01-16-2013, 11:04 PM   #7
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Sub Panel over 10g-2 Help Needed


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Originally Posted by hamblinh View Post
Are you talking about the clamp to hold the wires were they enter the panel? If so, I plan on going back and adding clamps once I make sure this is going to work. I also planned on stripping back the covering for the wires.
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Old 01-16-2013, 11:29 PM   #8
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Not legal using a 10-2. You'll either have to set a transformer to create a SDS neutral, or install a new feeder cable.
Ok. I have been checking out the SDS but i'm not sure if I understand.

Do I need to run a ground wire from the neutral bar to the panel case and a ground wire to a grounding rod from the neutral bar?
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Old 01-16-2013, 11:36 PM   #9
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Sub Panel over 10g-2 Help Needed


First choice is you can replace the underground cable with proper conductor and increase the size as well.

The reason why is so you can use full four conductor per modern NEC /CEC codes.

The photo you show us with 10-2 UF cable is only legit if you have only 120 volt load or straight 240 volts loads but never 120/240 volts loads the key issue is the " netural " conductor which you used as grounded conductor that is not a really safe spot to deal with it.

Second choice is use the transfomer run the 240 volt on primary side while on secondary side you can run 120/240 volts so you are creating a new netural location which we called SDS

Most peoples will genrally go with first option as I posted not very many will asked for transfomer on the shed circuit unless it have super long circuit run.

Merci,
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Old 01-16-2013, 11:54 PM   #10
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Sub Panel over 10g-2 Help Needed


Dig the wire up, roll it up, and take it back to Lowes! They take anything back!! Then get yourself some real wire
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Old 01-17-2013, 06:18 AM   #11
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Sub Panel over 10g-2 Help Needed


This install is totally non compliant and dangerous. There are no grandfather rules that will apply. You are using a bare ground wire as a current carrying conductor (the neural) and you do not have a proper ground.

Based on what you think is correct, you need to bring in an electricain.
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Old 01-17-2013, 07:27 AM   #12
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Sub Panel over 10g-2 Help Needed


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I know a subpanel in a separate location must be grounded locally, but does it also have to be grounded to the panel? Isn't there some prohibition against grounding in two places?
The first panel in the outbuilding must have a (typically #6 copper) grounding electrode conductor out to two ground rods (min. 8' each, min. 6' apart).

A subpanel must have an equipment grounding conductor from its frame (aka can; box) or grounding bus bar, accompanying the feed conductors, and connected to the grounding bus bar at the feeding panel.

There must be a master shutoff switch or breaker in the outbuilding, either in the first panel or before.

In the subpanel, neutrals have their own bus bar insulated from the frame and not connected to any ground wires (EGCs, GECs).

As was mentioned above, having just two insulated conductors (black and white) coming in, you can bring in 240 volts only or 120 volts only. Either way, being 10 gauge they will carry 30 amps.

If per chance you go with a transformer (not the favored approach), it is much more efficient to bring out 240 volts and step it down to 120 volts in the outbuilding compared with bringing it out as 120 volts and stepping it up to 240 in the outbuilding. Appliances using both 120 volts and 240 volts from a single cord and plug or 3 wire (hot, hot, neutral) leads may not be connected to a simple 240 to 120 volt step down transformer and also to the raw 240 volts; a 240 volt to 120/240 volt transformer with center tapped secondary is needed.

The "prohibition" is against having neutral and ground interconnected (bonded) at more than one spot, the correct spot being at the first main disconnect switch or breaker after the meter.

The "grandfathering" is the permitted continued use of an existing subpanel feed cable to a different building where there are 3 wires, each insulated, for two hots and a neutral and no EGC.

I would suggest digging up the #10 cable and installing #8 copper cable or conduited conductors (for 40 amps) or #6 (allows 55 amps) with red, white, and black for 120/240 volts. For either of these the 4'th conductor (EGC) can be #10.
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Last edited by AllanJ; 01-17-2013 at 07:52 AM.
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Old 01-17-2013, 07:53 AM   #13
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The first panel in the outbuilding must have a (typically #6 copper) grounding electrode conductor out to two ground rods (min. 8' each, min. 6' apart).

A subpanel must have an equipment grounding conductor from its frame (aka can; box) or grounding bus bar, accompanying the feed conductors, and connected to the grounding bus bar at the feeding panel.

There must be a master shutoff switch or breaker in the outbuilding, either in the first panel or before.

In the subpanel, neutrals have their own bus bar insulated from the frame and not connected to any ground wires (EGCs, GECs).

As was mentioned above, having just two insulated conductors (black and white) coming in, you can bring in 240 volts only or 120 volts only. Either way, being 10 gauge they will carry 30 amps.
Lets say he went to a 240v only subpanel. He would ground to the ground rods. But would he attach the existing ground wire to anything?
Or, if they have run individual wires in conduit with an insulated ground, could he have used it as a neutral?
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Old 01-17-2013, 08:11 AM   #14
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Lets say he went to a 240v only subpanel. He would ground to the ground rods. But would he attach the existing ground wire to anything?
Or, if they have run individual wires in conduit with an insulated ground, could he have used it as a neutral?
If he wires as 240 only, he would use the 2 insulated conductors as the hots, the bare wire as the ground. There is no neutral in the method. But it is moot as all his loads are 120 and he has to have a neutral.

This would lead to somebody using the ground as the neutral.
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Old 01-17-2013, 09:07 AM   #15
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If he wires as 240 only, he would use the 2 insulated conductors as the hots, the bare wire as the ground. There is no neutral in the method. But it is moot as all his loads are 120 and he has to have a neutral.

This would lead to somebody using the ground as the neutral.
Or add the transformer but that may cost as much as the correct wire would've.

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