Does ground wire conduit need to be bonded at both ends?

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vince440

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We are doing the underground on a large hospital project. We have run 1" PVC conduit underground between electric rooms. The elbows and risers are GRC. We are pulling an insulated conductor 3/0. The engineer has told us that the entire run must be steel so as to bond both ends or it must all be PVC. They say we cannot have a run with steel on both ends and PVC in the middle. I could understand if it were a bare conductor but not with insulated as long as we bond our riser at both ends. Any comments?
 
The engineer is correct, you are creating mutiple chokes. A bare conductor would actually be better in this scenario.


Roger
 
I should have included the article and section in my post above.

250.64(E)

(E) Enclosures for Grounding Electrode Conductors Ferrous metal enclosures for grounding electrode conductors shall be electrically continuous from the point of attachment to cabinets or equipment to the grounding electrode and shall be securely fastened to the ground clamp or fitting. Nonferrous metal enclosures shall not be required to be electrically continuous. Ferrous metal enclosures that are not physically continuous from cabinets or equipment to the grounding electrode shall be made electrically continuous by bonding each end of the raceway or enclosure to the grounding electrode conductor. Bonding shall apply at each end and to all intervening ferrous raceways, boxes, and enclosures between the service equipment and the grounding electrode. The bonding jumper for a grounding electrode conductor raceway or cable armor shall be the same size as, or larger than, the required enclosed grounding electrode conductor. Where a raceway is used as protection for a grounding electrode conductor, the installation shall comply with the requirements of the appropriate raceway article.
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Roger
 
Roger-- doesn't that mean you can bond both ends of the rigid. My understanding is he has GRC on both ends with PVC in the middle. I am reading the quote below and it appears to okay this installation

Ferrous metal enclosures that are not physically continuous from cabinets or equipment to the grounding electrode shall be made electrically continuous by bonding each end of the raceway or enclosure to the grounding electrode conductor. Bonding shall apply at each end and to all intervening ferrous raceways,
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Hi: I believe Vince is correct in bonding metal conduit at both ends. I've seen lots of pvc under gas station fueling areas and metal conduits emerging from them. Of course they have egc's in the runs.
 
Dennis Alwon said:
Roger-- doesn't that mean you can bond both ends of the rigid. My understanding is he has GRC on both ends with PVC in the middle. I am reading the quote below and it appears to okay this installation
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Dennis and Wbalsam1, in this scenario you would have four ends to bond to negate the chokes, how would you propose to bond the ends of the ferrous raceways connected to the PVC?

Edit to add once again, The engineer is correct.

Roger
 
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Here is an illustration that may help.

1100205275_2.jpg


Excerpt from the training material

CAUTION: The effectiveness of the grounding electrode could be significantly reduced if a ferromagnetic raceway containing a grounding electrode conductor isn?t bonded to the grounding electrode conductor at both ends. This is because a single conductor carrying high-frequency lightning current in a ferrous raceway causes the raceway to act as an inductor, which severely limits the current flow through the grounding electrode conductor. ANSI/IEEE 142, Recommended Practice for Grounding of Industrial and Commercial Power Systems (Green Book) states ?an inductive choke can reduce the current flow by 97 percent.?

Roger
 
I agree with Roger. If the RMC is not continuous (PVC is in the middle of the run) you cannot bond all 4 of the RMC ends.
 
oops

oops

Hi: I agree. I misread/misinterpreted the question and did not realize you were talking about a grounding electrode conductor. Duh! I'll be alright.
 
If we are talking about a conduit that contains a GEC, then I agree with Roger as well. But it is not clear to me from the OP that the grounding conductor in question is a GEC. The conduit runs "between electric rooms".
Vince, is this conductor a grounding electrode conductor, or is it an equipment grounding conductor run with the other conductors of a branch cirucuit or feeder? If it is a EGC, then there is no need to bond the metal conduit sections on both ends. Each section only needs to be bonded once, and the connection to the enclosure will probably take care of that requirement.
 
roger said:
The engineer is correct, you are creating mutiple chokes. A bare conductor would actually be better in this scenario.
Roger
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Now that I follow the rule, would someone please explain to me what multiple chokes are and what problems they can cause.
 
Eprice, the OP says it is a 3/0 in 1" PVC, this pretty much means there is not much space left in the conduit for circuit conductors. :smile:

Roger
 
Dennis,
The effectiveness of the grounding electrode could be significantly reduced if a ferromagnetic raceway containing a grounding electrode conductor isn’t bonded to the grounding electrode conductor at both ends. This is because a single conductor carrying high-frequency lightning current in a ferrous raceway causes the raceway to act as an inductor, which severely limits the current flow through the grounding electrode conductor.
Click to expand...

HERE is an old thread on this subject.

Roger
 
This conductor is part of a ground loop system that daisy chains all electric and data rooms. Terminating on a ground buss in each room. This will provide GEC for transformers etc.
 
roger said:
Eprice, the OP says it is a 3/0 in 1" PVC, this pretty much means there is not much space left in the conduit for circuit conductors. :smile:

Roger
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Ahh.. yes now I see :)
 
Vince, you'll have to take another route if you can not bond both ends of each ferrous metallic raceway that the GEC passes through.

Roger
 
Roger,

I have a question regarding this situation.

If the conductor is in PVC underground with GRC 90's on each end and PVC underground.

1.) Is this an acceptable installation?
2.) if it is acceptable do you need to bond the ends of the GRC that stub up through the poured slab? or should this be either all PVC or All GRC (or some other metal conduit)?

Just curious because I see this quite a bit on large projects that require (per the specifications) that GRC 90's be used to turn up through a slab.

Thanks,
Ed
 
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