Grounding or Bonding or Something Else?

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charlie b

charlie b

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Situation: New penthouse added to existing building. Both are concrete with steel rebar. Structural design for penthouse did not involve connecting new rebar with rebar of existing building. Transformer is installed in penthouse. Presently, the XO is connected to ?local? building steel, and is therefore not in electrical contact with planet Earth.

Solution: Chip away enough concrete, both in penthouse and in electric room on floor below, to gain access to the building steel on each floor. Run a ?wire? between the two.

Questions:
1. Will this work?
2. What do you call that ?wire?? Bonding Jumper? Grounding Electrode Conductor?
3. How do you size that ?wire?? 250.66? 250.122? Other?

My problem with this is that we are not really connecting two electrodes together, so we are not in 250.53(C). The building steel in the existing building is an electrode, but the building steel in the new penthouse is not (at least, not yet). So this plan will essentially cause the building steel in the new penthouse to become part of the grounding electrode system, and will cause the wire from XO to penthouse steel to become a successful connection to a grounding electrode.
 
I would think that is a legal install. What choice do you have? The Gec is bolted to the steel. I see no reason why a bond on the steel to connect the top and bottom to the EGS would be a problem. As long as the bond equals the GEC used and secured properly.....
 
I'll have to study the thread more, but my Building Inspector friends would strongly disagree with chipping to re-bar.
If it wasn't avaialable to you for bonding, I think it's best to go to plan "B".
 
charlie b said:
Situation: New penthouse added to existing building. Both are concrete with steel rebar. Structural design for penthouse did not involve connecting new rebar with rebar of existing building. Transformer is installed in penthouse. Presently, the XO is connected to “local” building steel, and is therefore not in electrical contact with planet Earth.

Solution: Chip away enough concrete, both in penthouse and in electric room on floor below, to gain access to the building steel on each floor. Run a “wire” between the two.

Questions:
1. Will this work?
2. What do you call that “wire”? Bonding Jumper? Grounding Electrode Conductor?
3. How do you size that “wire”? 250.66? 250.122? Other?

My problem with this is that we are not really connecting two electrodes together, so we are not in 250.53(C). The building steel in the existing building is an electrode, but the building steel in the new penthouse is not (at least, not yet). So this plan will essentially cause the building steel in the new penthouse to become part of the grounding electrode system, and will cause the wire from XO to penthouse steel to become a successful connection to a grounding electrode.
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Interesting question Charlie. I do question if this is permitted, although I'm pretty sure it's not explicity prohibited. I think the connection would be a grounding electrode connector, sized per 250.66 . The most questionable part, as you pointed out is that the new building rebar is not an electrode - but I don't know if you can use the "yet" logic. The situations where the metal frame can be considered an electrode are under 250.52(2), although I don't quite understand 250.52(2)(4) permitting "other approved means of establishing a connection to earth" - does this situation qualify?

Edit: also what is your interpretation of the 'exception' after 250.50?
 
augie47 said:
I'll have to study the thread more, but my Building Inspector friends would strongly disagree with chipping to re-bar.
If it wasn't avaialable to you for bonding, I think it's best to go to plan "B".
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I didnt think of what building would say you are probably right.
If he could get to the feeder shaft and ran the transformer GEC to the metal below would that solve this problem?
Would the top floor still have to be bonded some how to the floors below.
I may not be thinking clearly is why I am asking.:D
 
augie47 said:
I think it's best to go to plan "B".
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And that would be? Run a wire from XO all the way to the main electrical room, and hit the ground bar in that room? Or perhaps we'll go with Plan "C": Connect a "really long" wire from XO to a ground rod, then throw the rod out the penthouse window, hoping it impails itself deeply enough into the dirt below? :grin:
 
skeshesh said:
. . . also what is your interpretation of the 'exception' after 250.50?
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If the existing building (to which we added a penthouse) was old enough that, at the time of its construction, its steel reinforcement was not required to have been part of the grounding electrode system, then we don't have to chip away concrete in order to connect that steel to the grounding electrode system. Doesn't help in my present situation.
 
charlie b said:
Run a wire from XO all the way to the main electrical room, and hit the ground bar in that room?
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That's what I would consider one best solution. Or running to building steel that is bonded back to the main service (if you have any steel columns or beams).

Or, is the transformer fed with metal conduit? Any chance that is a suitable ground? That brings up a question I've been wondering about: If you know you are going to install a transformer where finding a proper ground is going to be a problem, can you run a larger ground wire with the transformer feeder, and then use it as the ground for the secondary?

Steve
 
steve66 said:
. . . Or running to building steel that is bonded back to the main service.
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I infer that you are saying there is a difference between (1) Connecting XO to the penthouse building steel, then bonding that steel to the steel in the floor below, and (2) Connecting XO to building steel in the floor below. The two share the characteristic of running a wire between floors, and chipping concrete on the floor below. To me, concept (1) seems more "obviously legal," and that might be the way we go.

Thanks for the suggestions. Anyone else have an idea?
 
charlie b said:
I infer that you are saying there is a difference between (1) Connecting XO to the penthouse building steel, then bonding that steel to the steel in the floor below, and (2) Connecting XO to building steel in the floor below. The two share the characteristic of running a wire between floors, and chipping concrete on the floor below. To me, concept (1) seems more "obviously legal," and that might be the way we go.

Thanks for the suggestions. Anyone else have an idea?
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I probably edited that post after you read it. By building steel, I was refering to columns or beams (if there are any). No concrete encased rebar.

Steve
 
Charlie:

I'm looking at 250.30(A)(7). I don't see where a CCE can be used as the grounding electrode for a separately derived system. It looks to me like it is either the first 5' of water pipe, or structural steel per 250.52(A)(2), or running back to the main service.

Edit: Opps, I missed 250.52(A)(4) which basically says other approved means. So maybe the rebar to rebar ground would be OK.

Steve
 
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In answer to the original questions:

1. Will it work?
I think so, but the biggest question in my mind would be the concern that Augie brought up about getting approval to chip to the rebar.

2. What to you call that wire?
I would call it a bonding jumper

3.How do you size that wire?
I think 250.66 would be the appropriate section.

I base my last two answers on the fact that what you are doing is similar to what you would do with exposed structural steel that was not intentionally grounded as covered in 250.104(C). You would be bonding the penthouse rebar to one of the grounding electrodes. I know it is not exactly the same as what 250.104(C) is talking about, but it is the closest fit that I can come up with.
 
I'm still iffy about the "other approved means" issue which I brought up before. Is there any guidelines as to what this means? Is this a referrence to having to check with AHJ first?

sidenote: one of the mechanical guys at our office used to have a pretty impressive javelin throw scholarship which apparently paid a good chuck of his college fees. I nominate him to put plan "C" in motion :grin:
 
charlie b said:
Because I would have to catch it within five feet of where it enters the building, and my problem is in the penthouse.
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I wouldn't make you do that since the coldwater is already bonded / grounded, yes I know what it says. I would talk to the AHJ and see what he says.

Is the transformer being fed from the main service of the building? You could just pull a ground up from there.
 
I now understand that the contractor is planning to run a ground wire from the penthouse to the main electrical room on the first floor, and hit the ground bar in that room. That should do the trick. Many thanks for the opinions and suggestions.
 
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