Electrical Supply Question

[Ken Massingale]

I need help settling a 'discussion' I'm having with a friend, please.

Case 1:
Electrical power (220 volt) to a detached building is from the main panel in a house, currently from a 60 amp breaker, to a 100 amp distribution panel (max 45 amp usage at any one time) in the detached building. Underground cable of the correct size.
Should the ground conductor be connected to the Ground/Neutral bar in the main panel in the house and to the ground/Neutral bar in the panel in the detached building, or should it not be connected in the main house panel and a dedicated ground rod be driven at the detached building and that ground used for the 100 amp panel in the detached building.


Case 2:
Same situation except that the supply to the detached building would be from the meter box on the house. Would one use the ground in the meter box or a ground rod at the detached building.

In both cases the building is ~75 feet from the house.

Thanks

[LJR]

There's a few variables and exceptions but in it's simplest form: Either way you describe for the source of electricity you will need to drive a ground rod at the detached garage for the garage ground. You may also need to run a ground wire from the house to the garage depending on are they connected by water pipe or gas pipe or something similar.

One of the easier sites I've found that talks about wiring methods is: http://www.selfhelpandmore.com/

[Ken Massingale]

Thanks. There are no water or gas connection between the 2 buildings. He may run water later but it would be in PVC.

[Hellrazor]

Ken,

I'll just answer case 1, I'm not touching the other idea with a 10' pole.

You will need to run 4 wires for that. 2 hot, 1 neutral and a ground. The out building should NOT bond the neutral and ground. You will need to install a ground rod at the building too.

[eezlock]

electrical question

Ken, that panel in the detached building is using what is called a sub fed panel ( meaning that it is powered from the main panel). According to electrical codes (NEC) the grounded conductor must be connected to an isolated neutral bar in the main service panel. Also, that sub fed panel in the
that building needs to have it's own ground rod driven into the ground
and connected there for the equipment ground connection.

What most people get confused with in electrical terminology is grounded and grounding. The neutral is the grounded conductor( electrical return path), the green or bare wire is the equipment grounding conductor (for safety). They are not the same and must be connected to proper terminals
at the distribution panels. Hope this helps and doesn't confuse you further.
eezlock

[Hellrazor]

Ken,

Here is a good reference that explains almost every option:

http://www.selfhelpandmore.com/homew...arageshowp.htm

[Ken Massingale]

Thanks for all the replies. I'm going to do some reading and I'm sure I'll have another question or 2 to make sure I understand what I think I understand.
k

[SARGE..g-47]

Good morning Ken...

I just went through the same as I just finished installing a sub panel with a 2nd 220V dedicated line in my shop last night. I had never done a sub panel before and got much help here as I wasn't certain and I won't make a connection till I am certain.

It's important what you have been told about not bonding the neutral to ground in the sub panel as it is already bonded in the main. I did not have to drive a ground in an Out Building as you seem to be doing with your panel. Inside the same facility doesn't require it.. but you have to do it to meet code for an Out building to meet code, at least here in GA.

I almost made the mistake of thinking that a second side of my neutral bar was the ground, but Larry G. pointed out that it was just an extention of the other side of neutral bridged by a metal strap. And.... that most sub panels don't come with a ground bar anymore and have to be purchased and installed. The good news is it only cost $1.25 and the sub panel box has 2 threaded reciever holes to accept the 2 screws that come with it. It attached directly to the box grounding the bar to the metal box and must be isolated from that neutral in the sub panel as stated. That's very important and please don't proceed until you understand that and why it is true.

Other than that... it's not a problem. The problem is how dry and cracked your hands are going to be after running 30 feet of new 220 V line, installing new outlets and stripping that monster wire for the new sub panel. I can barely move my right hand this morning. I'm getting old I think! ha.. ha...

Regards...

[bigangelman]

just did it myself

I just complete a job like this and the inspector made me put in 2 ground rods 5' apart for the sub panel in the out building. (1 ground line with 2 rods') I don't know why 2 but that what is took to get it too pass.

Tom

[Hellrazor]

2 is always better than one. Atleast that is my excuse with tools


New tool excuse: If you don't have a palm nailer, here is the time to get one. I use my palm nailer to drive the ground rods.

[JBCrooks]

Like others have said, split the ground/neutral in the outbuilding box. I am assuming that you are under Pickens county codes? If so, don't drive a new ground rod at the building. By the current codes, there should be 2 ground rods at the meter base, interconnected, 3' from the footings and 8' between ground rods. With Duke so close you can get around 4V difference between ground rods if they aren't connected directly together. Doesn't sound like much, but you can feel the tingle.

[Ken Massingale]

Like others have said, split the ground/neutral in the outbuilding box. I am assuming that you are under Pickens county codes? If so, don't drive a new ground rod at the building. By the current codes, there should be 2 ground rods at the meter base, interconnected, 3' from the footings and 8' between ground rods. With Duke so close you can get around 4V difference between ground rods if they aren't connected directly together. Doesn't sound like much, but you can feel the tingle.

Thanks JB, actually we are in Anderson County, barely. And we are on Blue Ridge, same codes?

[JBCrooks]

We very seldom work in Anderson, so I am not so familiar with their requirements. I don't think they require quite as much as in Pickens. I would just be leary about putting in seperate ground rods that aren't connected. We usually get one or two service calls a year where people do that and keep getting "shocked"

[Hellrazor]

I would just be leary about putting in seperate ground rods that aren't connected. We usually get one or two service calls a year where people do that and keep getting "shocked"

Thats odd since every outbuilding install I've ever been on had a seperate ground rod. I could see a problem if someone bonds the ground and neutral bar on the subpanel. How/where were they getting shocked?

[Jeffrey Schronce]

Electrical power (220 volt) to a detached building is from the main panel in a house, currently from a 60 amp breaker, to a 100 amp distribution panel (max 45 amp usage at any one time) in the detached building. Underground cable of the correct size.
Should the ground conductor be connected to the Ground/Neutral bar in the main panel in the house and to the ground/Neutral bar in the panel in the detached building, or should it not be connected in the main house panel and a dedicated ground rod be driven at the detached building and that ground used for the 100 amp panel in the detached building.

I have pretty much this identical set up. I do have a question as to why I have this set up? LOL! I have 200 AMP main in the house that has a 60 AMP breaker that runs underground to the detached shop. The shop has a 100 AMP main breaker. Why the difference?
BTW, my subpanel is grounded at the detached garage (I assume since there is a huge ground rod in the ground which is connected to the box).