G.E.C. in emt

[jmargolis79]

I have a GEC that is ran in emt for the last 5 feet by the panel to protect it. Another JW is sure that the Emt has to be bonded on both sides ( the top and the bottom or in the panel). He said it's in the 08 nec but could not find it. Does this sound right and were is it?

 

[Dennis Alwon]

look at 250.64(E)

 

[infinity]

Here's a graphic:

 

[ericsherman37]

I'm probably wrong because I'm going off of 3rd-hand knowledge and hearsay, but I understand that enclosing a GEC in a ferrous raceway by itself would have a similar effect in the event of, say, a lightning strike, as you would see in running a phase conductor in a ferrous raceway by itself.

Something about the magnetic field (which isn't cancelled out by conductors of other phases or neutrals or anything) created by the current through the GEC inducing eddy currents in the metal raceway, which impede the current flow through the enclosed conductor. Something of a "choke" effect. Therefore the ferrous raceway would have to be bonded at both ends.

Perhaps someone can elucidate this for me if I have it incorrect.

 

[ericsherman37]

If it's possible to sleeve it in PVC instead, that would eliminate the problem. Technically I suppose you'd have to use PVC or other non-ferrous locknuts too :roll:

 

[Dennis Alwon]

If it's possible to sleeve it in PVC instead, that would eliminate the problem. Technically I suppose you'd have to use PVC or other non-ferrous locknuts too :roll:

I don't think so ... the pvc pipe passes thru a metal enclosure-- what would you do there?

 

[Howard Burger]

Helpful ? quote from SOARES

Helpful ? quote from SOARES

FWIW, in the Soares book on grounding and bonding, p 131 it states in regards to using an 8 AWG grounding electrode conductor protected by metalic armored cable:

"The need for bonding the metalic armor or such cable is required in 250.64(E). Where that bonding procedure is not followed, the impedence of the grounding electrode conductor is approximately doubled with the result that its effectiveness is markedly reduced."

The paragraph before this talks about bonding both ends of a GEC to a ferrous metal raceway. (I've noticed in several spots that the authors of Soares, as with the NEC, don't follow good writing practices and a statement of fact, like the one above, which really apply to several examples cited, is placed such that a person could think it only applies to the last example.)

I think what they're saying is that failure to bond reduces the ability of the GEC to effectively conduct fault current. By half, if 'impedence...is doubled'?

Perhaps Larry of Charlie could comment on this.

 

[roger]

I don't think so ... the pvc pipe passes thru a metal enclosure-- what would you do there?

Dennis, since the GEC attaches to this enclosure it wouldn't matter.

If one chose to use mineralac straps with metal screws there would be a problem in that it would be installing chokes around the GEC.

Roger

 

[Dennis Alwon]

Dennis, since the GEC attaches to this enclosure it wouldn't matter.

If one chose to use mineralac straps with metal screws there would be a problem in that it would be installing chokes around the GEC.

Roger

Roger I was responding to the post about creating a choke with a locknut. He stated a pvc locknut would be needed. I said the pvc passes thru the can so whats the difference. The metal locknut will be bonded to the can so there is no issue. I think we are on the same page.

 

[roger]

I think we are on the same page.

I think we are too, I missunderstood.

Roger