egc in metal raceway

[sparkmantoo]

say i have a raceway of emt from a panel to a metal box and i want to put a receptacle in that box. i pull a hot, neutral and a ground wire. now my conduit can be used as the equipment ground but i choose to pull a ground with the circuit and it is not an isolated receptacle. am i required to connect that ground wire to the box. if so, doesn't that provide a parrallel path for the fault current to flow? remember that the conduit is all ready grounded. i await some input on this one.

215.118 250.146 A,B,&D(fpn)

 

[don_resqcapt19]

Re: egc in metal raceway

Yes, you are required to connect the EGC to the box. Parallel paths for fault current are not a problem. It is parallel paths for the grounded (neutral) conductor that cause paroblems, not parallel paths for grounding conductors. Parallel grounding paths are required by some sections of Article 517.
Don

 

[sparkmantoo]

Re: egc in metal raceway

why? if the box is all ready grounded by the conduit, why do i need to attach that wire to the box? it is a ground not a bond wire. if i didn't pull a ground then i would have to attach a BOND wire from the box to the device correct? i believe that the purpose of the ground, and correct me if i am wrong, is to provide a direct, low impedance path back to ground so to help in the operation of the ocpd. metal racweways that enclose a grounding electrode conductors, have to be bonded at both ends of the raceway and that is in parrallel. when you have a piece of nm cable then i agree that the ground wire is to be attached to a metal box.

 

[tom baker]

Re: egc in metal raceway

Sparkman, yes you have to bond the equipment grounding conductor to the box, but a 2002 change does not require this if you are pulling through the box with no splices or devices in the box.

Are far as the metal raceway being bonded at both ends, thats when you are enclosing a grounding electrode conductor, for an entirely different reason. By bonding all equipment grounding paths together, you create the lowest possible impedance back the source for fault current.

 

[don_resqcapt19]

Re: egc in metal raceway

First, in my opinion, all of what we now call equipment grounding conductors, are really equipment bonding conductors (but that is another subject). The connection of the EGC that is in the EMT to the metal box will create a better fault return path than either of of them alone. Many times the conduit couplings are not treated as electrical connections and the fault clearing path isn't really there, or the conduit is not properly supported and the couplings pull apart. I'm not sure of the substatiation for the original proposal that required this connection. It predates my code books. The oldest code that I have is the '78 and the requirement is in that edition.
Don

 

[sparkmantoo]

Re: egc in metal raceway

so what happens when i have a disconnect switch with eccentric knockouts and i have to use a bonding bushing? do i loop the egc through the bushing and then take it to the can or do i have to install a seperate bonding jumper from the bushing to the can?

 

[gwz2]

Re: egc in metal raceway

SPARKMANTOO,

I believe you left out an important section reference in your first post, 250.148.

When it is chosen, by the design engineer, owner, or craftsman, to use a wire conductor for additional ground fault return path [ 250.4(A) ] then 250.148 is required to be followed.

Like other's have mentioned, metal raceways do come apart because of poor installation practices, abuse, rust and other reasons.

Follow the 250.148 requirement and have a better (safer) installation.

As for the bonding bushing on concentric KO's, If a bonding bushing is used then bond it to the metal enclosure or to the EGC.

This is not a GEC discussion.

 

[charlie]

Re: egc in metal raceway

First, in my opinion, all of what we now call equipment grounding conductors, are really equipment bonding conductors (but that is another subject).

Don, the proposal to call "equipment grounding conductors" "equipment bonding conductors" has failed to get enough votes during the proposal stage. Panel 5 accepted it in session but didn't have the required 2/3 during the balloting. The TCC is reporting it as a failed proposal in the proposal stage. If you would like to see it in the Code, I recommend you put a comment in to support this proposal. I suspect bennie will put in a comment against this proposal.

 

[don_resqcapt19]

Re: egc in metal raceway

Charlie,
I would expect that there will a large number of comments on both sides of this issue. I was very suprised to see that the proposal even got a majority vote from CMP5. It is rare that a change of this magnitude passes on the first go around.
Don

 

[bennie]

Re: egc in metal raceway

I respect Don's effort in this issue. I have had conversations with a Phd from the U of O, an electronics professor. The electronics and engineering community would contest this change of definition.

I will support a proposal to delete "ed" and "ing".

Describing what something will do, or has done, is not high grade technical writing.

 

[sparkmantoo]

Re: egc in metal raceway

okay people lets get back on track hear. i am not asking what some panel decided to call a egc or a ebc, i was asking a simple question. qwz2, i never said anything about splicing and that is why i didn't include it in my post and i am perfectly aware of the fact that this is not a gec discussion, i opened the topic. as for the bonding bushing part you said to bond it to the can OR to the egc, do you do it to both? loop it through the bushing and then go to the can. is this acceptable?
the reason i cited 250.118 is that i do not have to pull a egc, if i use any of the egc that 250.118 lists. i also agree that it is not a good practice to rely on the raceway to provide adequate grounding. this i why i chose to pull that ground to give a better ground for the system.
250.146 say that i don't need a bonding jumper in certain situations. i chose to put this in for the same reason, a safer system.