How to Ground

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czars

Czars
Location
West Melbourne, FL
Occupation
Florida Certified Electrical Contractor
I have a customer that presently has a 120/240 V, 100A service into his home. We are upgrading his service to 200A and of course we will be upgrading his service panel to a new one with seperated neutral and ground connections. He has a sub-panel in his garage which will also be changed to a panel with seperate ground and neutral connections. The old subpanel is connected to the copper cold water pipe in the garage and so will the new subpanel. The Feeder to the sub-panel consists of three insulated conductors and no ground conductor. The feeder is buried and it is not feasible to change it to a cable with an integral ground.

If we retain the present feeder (without a ground conductor), what is the proper method to provide a ground at the subpanel. Is the connection to the cold water pipe sufficient? Should we also install a new ground rod at the garage? What can we do without installing a new feeder cable?
 
czars said:
We are upgrading his service to 200A and of course we will be upgrading his service panel to a new one with seperated neutral and ground connections.
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The "of course" part bothers me here. While I'm all for being helpful, it's a sign that you need to subcontract out the electrical service to someone with the proper training and (if needed) license.

czars said:
If we retain the present feeder (without a ground conductor), what is the proper method to provide a ground at the subpanel. Is the connection to the cold water pipe sufficient? Should we also install a new ground rod at the garage? What can we do without installing a new feeder cable?
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That electrician you need to hire will be installing a new feeder for this one. I'm assuming the garage is detached, but the presence of that cold water pipe (which I further assume comes from the house) eliminates any chance of a 250.32(B)2 exception.
 
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Exception

Exception

I do not have my code book handy (it's at work) but I will give this a shot even with the exception I believe it also states that you can only do this (have another bonded connection N & G for a separate building on the same site) as long as there is not gfci protection involved but a grage is required to have it's receptacles gfci protected. I apoligize if this is not the exception you are refering to I am just shooting from the hip here in reference to the code exception. the water pipe is the key why not just run phase conductors, neutral, and ground?:smile:
 
CZAR, you need to clarify some things like is this garage with a sub-panel detatched? If so the answer is clearly defined in 250.32. If not you have no choice but to run 4-wires like it or not.
 
czars said:
The Feeder to the sub-panel consists of three insulated conductors and no ground conductor. The feeder is buried and it is not feasible to change it to a cable with an integral ground.
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So the existing subpanel feeder is a cable without an EGC?
 
czars said:
The Feeder to the sub-panel consists of three insulated conductors and no ground conductor. The feeder is buried and it is not feasible to change it to a cable with an integral ground.

If we retain the present feeder (without a ground conductor), what is the proper method to provide a ground at the subpanel. Is the connection to the cold water pipe sufficient? Should we also install a new ground rod at the garage? What can we do without installing a new feeder cable?
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The proper course of action may well involve installing the correct feeder, regardless of its lack of feasibility.

Another option might be to convert the existing feeder from 120/240V to 120V only if it is really not feasible to change it.
 
Folks, looking at Czar's post record, I do not see any reason to continue with the "hire an electrician" posts.

Just because someone asks a question in a unfamiliar tone does not necessarily mean that they are foreign to the trade; I know I've had several conversations where I knew the seasoned electrician I was talking to was hearing what he expected to hear, and not what I was saying. The confusing language of the NEC is largely to blame for this. :)

Anyway, I just wanted to say, if you want to help, help. If not, don't. Let's not tug the thread towards off topic anymore. ;)
 
Thanks for your response George. I always try to ask the opinion of other qualified folks when I move into unfamiliar territory. In this case, the garage is detached and the water pipe enteres the garage from the street and then goes to the house. There is a bond to the water pipe in the garage to the sub-panel (from the cold water input to the water heater), but there is no bond to the water pipe in the house. The feeder from the house to the garage is a cable with three insulated conductors with no ground.
 
So,
  • The electrical service is on the hosue.
  • The water pipe goes from the street, to the garage, to the house.
  • The feeder from the house to the garage has no EGC.
Each building is required to have a GES (Grounding Electrode System) connected to each electrical system. You create the GES normally at each structure.

Since there is no EGC in the feeder at the detached garage, then you must bond the EGCs of the circuits to the neutral conductor of the feeder, at the panel.

For more, check out this, this, and see what catches your eye on the table of contents of the FAQ.
 
czars said:
... He has a sub-panel in his garage which will also be changed to a panel with seperate ground and neutral connections. ...
If we retain the present feeder (without a ground conductor), what is the proper method to provide a ground at the subpanel. Is the connection to the cold water pipe sufficient? Should we also install a new ground rod at the garage? What can we do without installing a new feeder cable?
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I am going to follow George's lead on the appropriateness of answering this question.

However the above question strongly indicates a flawed understanding of grounding.

The most important aspect of what we call 'grounding' has nothing to do with ground at all. Instead it is the intentional _bonding_ of all conductive metal bits that are not intended to carry current, in order to provide an 'effective path' back to the source of supply. The idea is that in the event of a fault between a hot conductor and some random chunk of metal (say a water pipe) you will get a short circuit that will trip the breaker, rather than an energized chunk of metal.

An important feature of this bonding is that we have turned things that are not intended to carry current into good potential circuit paths. So the next part of bonding design is to mitigate any 'objectionable current' on the bonded metal. This means eliminating multiple connections between the electrical system and the bonded metal. If there is _one_, but only _one_ connection between the electrical system and the bonded metal, then there will be no closed circuit that includes the bonded metal, and thus no current flow on the bonded metal.

This boils down to (but only roughly): at the service the electrical system neutral is connected to both an earth grounding electrode, and to all of the bonded metal. At all other points in the electrical system, the bonded metal is maintained electrically isolated from the electrical system neutral. Generally this means that subpanels have a _separate_ ground and neutral, and feeders to the subpanel have separate neutral conductors (more correctly called _grounded conductors_) and ground wires (more correctly called _equipment grounding conductors_).

There is an exception: for detached structures, if there are no _bonded_ metallic paths between the structures, you are permitted to bond the neutral to your bonded metal. In essence the neutral itself is used as the effective path between the buildings. However this also means that the earth itself is a 'parallel path' between the structures, and some amount of the 'neutral current' will end up flowing through the earth. If there is ground fault protection on the service or the feeder, then you can't do this, and if there is a solid metallic path between the two structures, then you cannot do this.

So, what to do:
1) Put in a new feeder which has separate ground and neutral. Take this chance to bury a conduit to help with future repair and expansion.
2) Eliminate any bonded metal between the two structures; possibly with a length of plastic in the underground water line.
3) Somehow re-apply the current three wire feeder to have separate hot, neutral, and ground conductors.

-Jon
 
czars,
250.32 answers your question in detail. Refer to it and see which scenerio fits your application. George provided you a link with good pictorials.
 
Jon, thanks for the correction - I'd forgotten that there was a continuous metal water pipe between the structures when I posted my response. :cool:

In that case, an EGC in the feeder to the garage is required.
 
georgestolz said:
Just because someone asks a question in a unfamiliar tone does not necessarily mean that they are foreign to the trade;
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Now, now, I wasn't trying to bash him with my comments (way back in post #3) about hiring an electrician. As you know, I'm a bit of an anarchist about that stuff, I'm all for contractors, homeowners, et al being able to do at least some electrical work and plumbing even if they're not electricians or plumbers. :)

I was concerned from the start when he said "of course" he was replacing the service panel and would keep neutral and grounds separated. There's no "of course" about it, he's got to bond them at that point. When someone is certain he needs to do something that is in fact wrong, it justifies a concern that he may need to hire that job out.

I also helpfully suggested that the presence of the water pipe eliminated any chance of his re-using the original feeder as is. I notice you just caught up with that one in your last post. :)
 
I took the quoted text in a different way, which I will add to in blue:

czars said:
We are upgrading his (as in: adding a new)service to 200A (ahead of the existing) and of course we will be upgrading his (existing) service panel to a new one with seperated neutral and ground connections.
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If the new service has the main bonding jumper, then of course the box containing the original feeder/branch circuit conductors (where the original service once existed) would need to have the neutrals and grounds seperated.

That's how I interpreted the original post, and I can understand why the original post could be read several different ways. :)

I also helpfully suggested that the presence of the water pipe eliminated any chance of his re-using the original feeder as is. I notice you just caught up with that one in your last post. :)
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:D

Well, I took it as a given that I would install a non-metallic section in the water lateral between the two structures to avoid having to dig a trench across the yard. I had so locked-in that mindset that I had accepted it as fact and moved on wordlessly, which had the result of making me look like a flake. :D

I pride myself on my communicative abilities and sometimes I screw up royally. This is one such time. :)

I've told you privately but I will make it clear for all publicly, that I wasn't trying to pick on any of the three that questioned his qualifications, I was just trying to gently put that issue to rest so that the topic didn't go off track.
 
georgestolz said:
I've told you privately but I will make it clear for all publicly, that I wasn't trying to pick on any of the three that questioned his qualifications, I was just trying to gently put that issue to rest so that the topic didn't go off track.
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I know. I was just having some fun with you, since you were off today. :)
 
could you run 240 w/o a neutral using the thrid wire in the existing feeder as an EGC to the garage, use a transformer to create 240/120 3 wire in garage? Would that not qualify as an SDS?
 
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