GEC raceway

[yired29]

Can a GEC be installed in FMC?

250.64 (B) Securing and protection against physical damage

it shall be in RMC, IMC, PVC, EMT, or cable armor.

I see it in FMC all the time but by omission would it not be allowed?

I believe it is not allowed.

 

[Dave58er]

I see it in FMC all the time

I don't think I've seen a GEC in flex, only RMC or RMNC. In most cases it isn't subject to physical damage and only gets sleeved for looks at the points where it runs straight, either along a wall or up it for example.

As for your question of is it allowed I would agree its not. But I do have to ask a stupid question, in what article will I find "cable armor"?

This doesn't ring a bell and I may not be familiar with it.

 

[yired29]

I don't think I've seen a GEC in flex, only RMC or RMNC. In most cases it isn't subject to physical damage and only gets sleeved for looks at the points where it runs straight, either along a wall or up it for example.

As for your question of is it allowed I would agree its not. But I do have to ask a stupid question, in what article will I find "cable armor"?

This doesn't ring a bell and I may not be familiar with it.

I see GEC in FMC on separately derived transformers all the time. FMC from the transformer to a change over fitting to EMT then up wall to building steel. I think this is a violation.

 

[Dave58er]

It's not SOP around here, I guess because its against code.

There's a few of thoughts I have on all this, in random order;

-Is the EMT you describe in violation of 250.64(E)

-Why even use the flex?

-Looking at the title of the article: "....and protection against physical damage." and also at 348.12 (7) I can see why FMC wouldn't be mentioned.

-Still wondering what this "cable armor" is.

 

[infinity]

IMO it's not a violation if the GEC is not being protected from physical damage in the first place. If the GEC does not require protection then I see on reason why you cannot use it. Cable armor is like a piece of AC cable usually with a single solid conductor in it.

 

[Dave58er]

This is a horse that may have died a long time ago but it really intrigues me.

At first I was leaning toward your interpretation Rob but I wasn't willing to go that far.

4 AWG and larger seems to be able to be protected however you want as long as other articles aren't violated.

Speaking of 6 AWG;

"....free from exposure to physical damage shall be permitted to be (installed) without metal covering......."

Once you decide to use metal covering are you not forced into one of the described wiring methods?

Also does this wording say you can't use a metal wiring method or protection unless it is exposed to physical damage. The same way 1/0 and larger "shall be permitted" to be run in parallel means smaller can't be?

As far as smaller than 6 AWG I don't see an allowance for other wiring methods when not subjected to physical damage. At first I thought the title alone would make it only apply to those areas but then that would seem to be contradicted by the wording for size 6 wire.

 

[infinity]

I don't see how you can require something that isn't required in the first place. If the GEC is run and does not require physcial protection then why should you be required to use a specific wiring method if you choose to install one?

 

[raider1]

I don't see how you can require something that isn't required in the first place. If the GEC is run and does not require physcial protection then why should you be required to use a specific wiring method if you choose to install one?

I agree, a GEC can be run in FMC when not subject to physical damage.

Keep in mind that 250.64(E) would apply and you would have to bond both ends of the FMC to the GEC.

Chris

 

[Volta]

I agree, a GEC can be run in FMC when not subject to physical damage.

Keep in mind that 250.64(E) would apply and you would have to bond both ends of the FMC to the GEC.

Chris

Unless aluminum. Then again, you'd probably need to find non-ferrous connectors to truly skip the bonding.

 

[raider1]

Unless aluminum. Then again, you'd probably need to find non-ferrous connectors to truly skip the bonding.

Correct, 250.64(E) only applies to ferrous raceways and enclosures.

Chris

 

[iwire]

I agree, a GEC can be run in FMC when not subject to physical damage.

I agree that makes sense I am not so sure it meets the NEC. Can I run an undersized wire EGC in a conduit that qualifies for a EGC?

 

[raider1]

I agree that makes sense I am not so sure it meets the NEC. Can I run an undersized wire EGC in a conduit that qualifies for a EGC?

I can see that a strict reading of 250.64(B) could require that a GEC could not be installed in FMC, LFMC, ENT, LFNC, a wireway ect...

Chris

 

[Volta]

I agree that makes sense I am not so sure it meets the NEC. Can I run an undersized wire EGC in a conduit that qualifies for a EGC?

I can see that a strict reading of 250.64(B) could require that a GEC could not be installed in FMC, LFMC, ENT, LFNC, a wireway ect...

Chris

At least if it is smaller than #4.

 

[lakee911]

Keep in mind that 250.64(E) would apply and you would have to bond both ends of the FMC to the GEC.

Both? I thought bonding was at one end only?

 

[yired29]

On a different subject, 250.64(B) does not permit flexible metal conduit as the enclosure for grounding electrode conductors AWG 6 and smaller. The reason for this is the conductor and enclosing raceway are in parallel?the raceway must be connected at both ends as required by 250.64(E). Metal flex has a much higher resistance than the other raceways permitted in 250.64(B) because the oil used in the manufacture of the flex makes in effect the resistance based on the cross section of the steel pulled out to its entire length, approximately three times the length of the run. Due to the skin effect, especially in the larger wire sizes, only 3 percent of the current flows in the grounding electrode conductor, while 97 percent flows in the enclosing metal raceway. The relatively high resistance of the flex makes it a poor choice to enclose the grounding-electrode conductor. The question then arises, why does 250.64(B) not specify which raceways shall be used for AWG 4 and larger conductors? It is more important that flex not be used for the larger conductors, but no such requirement is mentioned in 250.64(B). EC

I found this at
http://www.ecmag.com/?fa=article&articleID=5968&zoom_highlight=250.64+B+
September 2004

 

[raider1]

Both? I thought bonding was at one end only?

Yes, both ends must be bonded. When a GEC is run in a ferrous metal raceway the GEC must be bonded to the enclosure or raceway at both ends. This helps reduce the inductive "choke" effect that happens when high frequency lightning induced current flows through a GEC.

Chris

 

[yired29]

5-184 Log #450 NEC-P05 Final Action: Reject
(250.64(B))
____________________________________________________________
Submitter: W. Creighton Schwan, Hayward, CA
Recommendation: Insert a new third sentence to read:
Where protection is provided by a raceway, it shall be RMC, IMC, RNC, or
EMT.
Substantiation: The last sentence prohibits the use of flexible metal conduit
for enclosing a grounding electrode conductor smaller than 6 AWG. This
makes sense, because current flow in a single conductor in a metal raceway is
approximately 90 percent on the raceway, 5 percent on the conductor. Flexible metal conduit is a relatively poor conductor due to the oil used in its
manufacture interrupting the turn-to-turn conductivity and resulting in a metal ribbon conductor three times the length of the raceway itself. This added sentence will make the rule the same for 4 AWG and larger as it is for 6AWG and smaller.
Panel Meeting Action: Reject
Panel Statement: The submitter has not provided technical substantiation that would restrict the current accepted use of listed bare armored conductors for use as grounding electrode conductors, which is a current common practice. There is no evidence provided that indicates there is a problem with these types of cables installed as grounding electrode conductors.
Number Eligible to Vote: 15
Ballot Results: Affirmative: 15

This is ROP A2007
http://www.nfpa.org/assets/files/PDF/ROP/NEC2008Article250-280.pdf

 

[Dave58er]

I can see that a strict reading of 250.64(B) could require that a GEC could not be installed in FMC, LFMC, ENT, LFNC, a wireway ect...

Chris

To paraphrase Nicholson in "A Few Good Men": is there another kind of reading?

It doesn't seem like you could call an inspector strict if he cited an 8 AWG GEC in flex as a violation. IMO they went out of their way to not allow flex for this application.

I've never seen a GEC in flex. If I had it would have raised red flags to me for 250.64(E) but if that were satisfied I don't think I would have, up until this thread, realized there may be a violation of (B) depending on size.

And I have actually read this article before! :roll: I guess I was always paying too much attention to what sizes had to be protected and not how.

Learning new things is why I'm here.

 

[infinity]

It doesn't seem like you could call an inspector strict if he cited an 8 AWG GEC in flex as a violation. IMO they went out of their way to not allow flex for this application.

I agree, the #8 needs protection by one of the raceways mentioned 250.64.