250.64 GEC Raceway

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crossman

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This was discussed in a recent thread. I would like to get further opinions on the photo below (the photo is a mock-up used for training).

Here we have a xfmr (seperately derived system) with a #8 grounding electrode conductor installed in flexible metal conduit. At the waterpipe, the flex is terminated to the ground clamp. At the xfmr, the flex is connected with a 90 degree flex fitting.

Question 1: Using 250.64(B), is the flexible metal conduit as an enclosure for the GEC permissible?

Question 2: Does the 90 degree connector require a bonding bushing and bonding jumper to the case?

250-64B.jpg


Edit: corrected grammar
 
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Grounding electrode conductors smaller than 6 AWG shall be in rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, electrical metallic tubing, or cable armor.
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250.64(B) is fairly clear. GEC smaller than #6 have to run inside of one of the specified raceways.

I say violation.
 
crossman said:
Question 1: Using 250.64(B), is the flexible metal conduit as an enclosure for the GEC permissible?
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No

crossman said:
Question 2: Does the 90 degree connector require a bonding bushing and bonding jumper to the case?
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Connectors must be bonded on each side to avoid a possible choke action in the event the GEC is used.
 
On question 1, what would be the theoretical reason for not allowing the GEC to be installed in a 3 foot long piece of FMC?

On question 2, the 90 degree connector is bonded to the enclosure by means of the locknut. The GEC is also bonded to the enclosure, either directly, or through the SBJ. So is the bonding bushing/jumper really needed?
 
crossman said:
On question 1, what would be the theoretical reason for not allowing the GEC to be installed in a 3 foot long piece of FMC?

On question 2, the 90 degree connector is bonded to the enclosure by means of the locknut. The GEC is also bonded to the enclosure, either directly, or through the SBJ. So is the bonding bushing/jumper really needed?
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1. Who knows. Could be an oversight. Why isn't FNC allowed?

2. I seem to recall a locknut is not allowed to be used for this purpose.
 
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petersonra said:
1. Who knows. Could be an oversight.
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Maybe I should pursue this. Been in the trade since 1980, maybe it is time I had some input into the making of the NEC. At least I could get an explanation on the intent, and maybe an explanation of what cable armor is.

petersonra said:
2. I seem to recall a locknut is not allowed to be used for this purpose.
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I know there are some restrictions on using locknuts for the service entrance conductor raceways. I don't know of anything that states this for a GEC raceway.

I am definitely interested in knowing what everyone's opinion of this is, because I am not certain of what needs to be done.
 
petersonra said:
250.64(B) is fairly clear. GEC smaller than #6 have to run inside of one of the specified raceways.

I say violation.
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So what is cable armor? Is metal flex not cable armor?
 
guggemos said:
#1 is no. FMC is not allowed. Isn't BX cable armor?
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I don't know that BX is cable armor. I don't know of anything which is directly referred to as "cable armor". The question becomes "what did the NEC CMP mean when they used the term "cable armor".

Also, when would we ever use bx (AC cable) as a GEC? Single conductor armored ground? I never thought of that as being AC cable. Is it?

guggemos said:
#2 is yes a bonding bushing & jumper is req'd. to bond to the case.
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Can you give me a code section on that please?
 
This is from an Anixter Cable site:
Armored cable is normally used in applications where the cable is expected to be exposed to a harsh mechanical environment or where Type MC (metal clad) cable is required by the NEC (National Electrical Code). For example, armor is often specified for directly buried cables where rocks in the backfill could damage the cable. Armored cable is also frequently used in cable trays to protect the cable from falling objects, to provide added fire resistance and to provide additional safety for electrical maintenance workers.
Cable armor is generally one of three basic types: interlocked aluminum, interlocked galvanized steel, or corrugated-and-welded aluminum (Philsheath(R) for example). Other specialized types are also available. Many, if not most, applications can be satisfactorily served by either aluminum or steel armor.
Code ref: 250-80, 250-90, 250-96, 250-97 and I can't think of anymore. I'm also using a project req'd NEC 2002.
 
guggemos said:
#1 is no. FMC is not allowed. Isn't BX cable armor?
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Bx is armored cable. AC type.

Seems like it is picky but cable armor could be different from armored cable. I suspect they mean AC cable.
 
Those code references do not require a bonding bushing and jumper. IMSO, the contact of the fitting shoulder to the metal enclosure, and the locknut are okay as the bonding means.
 
Dennis Alwon said:
Bx is armored cable. AC type.

Seems like it is picky but cable armor could be different from armored cable. I suspect they mean AC cable.
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I haven't taken the time to look, but is armored cable manufactured with a single conductor? I know there is the stuff called "armored ground" that is like AC cable with a bare wire in it, but is recognized as being AC cable?

I guess the main question is, what is wrong with a 3 foot piece of FMC around a #8 GEC?
 
Art 320.2 says that AC cable consists of insulated conductors in a flexible metallic enclosure.

So technically, armored ground is not AC cable and I also don't see how there could be single conductor AC cable.

So what is cable armor?

and say we have an outdoor xfmr. I can't put the GEC in sealtite? Doesn't make sense to me.
 
crossman said:
On question 1, what would be the theoretical reason for not allowing the GEC to be installed in a 3 foot long piece of FMC?

On question 2, the 90 degree connector is bonded to the enclosure by means of the locknut. The GEC is also bonded to the enclosure, either directly, or through the SBJ. So is the bonding bushing/jumper really needed?
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I'm not sure if I can answer your conserns but in light of the reasons for the GEC it may be best to spend the additional effort, previous discussion :)
 
Given that there are limitations placed on flexible metal conduit serving as a type of equipment grounding conductor by 250.118,.. I would not want to use it for the grounding electrode conductor ,..bonded or not.
 
M. D. said:
Given that there are limitations placed on flexible metal conduit serving as a type of equipment grounding conductor by 250.118,.. I would not want to use it for the grounding electrode conductor ,..bonded or not.
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M.D. there is a #8 copper wire in the fmc.
 
The code does not allow FMC to enclose a GEC as the spirals are not shorted out as in AC cable and create an choke.
There is a difference between armor cable and cable armor. 4 AWG is available with armor, but its seldom used.
 
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