Armored Cable and EGCs

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mikehughes8

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I have a few questions regarding direct buried armored cable.

320.108 Equipment Grounding Conductor.

Type AC cable shall provide an adequate path for fault current as required by 250.4(A)(5) or (B)(4) to act as an equipment grounding conductor.

How does one determine whether or not AC cable make an adequate EGC. Does it have an equivalent wire size?

250.84 Underground Service Cable or Raceway.
(A) Underground Service Cable. The sheath or armor of a continuous underground metal-sheathed or armored service cable system that is connected to the grounded system conductor on the supply side shall not be required to be connected to the grounded system conductor at the building or structure. The sheath or armor shall be permitted to be insulated from the interior metal raceway or piping.

If a utility XFMR is feeding a Main Distribution Panel that in turn feeds sub-panels on different buildings am I correct that under this code reference I would connect the armor at the utility and omit that connection at the service equipment? Or do I have to maintain continuity up to the sub-panels on each building?
If I am not allowed to omit this connection wouldn't I be creating a parallel path back to the source using the armor and the grounded conductor?

310.7 Direct-Burial Conductors.
The metallic shield, sheath, or armor shall be connected to a grounding electrode conductor, grounding busbar, or a grounding electrode.

In all other cases the armor is required to be connected to a ground bus etc. If it does not meet the requirements of an EGC IAW Art 250.4 a supplemental EGC must be utilized. Is this a correct assessment?
 
mikehughes8 said:
320.108 Equipment Grounding Conductor.

Type AC cable shall provide an adequate path for fault current as required by 250.4(A)(5) or (B)(4) to act as an equipment grounding conductor.

How does one determine whether or not AC cable make an adequate EGC. Does it have an equivalent wire size?
Click to expand...


If it was listed as Type AC, I would think that the sheath is adequate by design.
 
AC cable is not a permitted method for services. 230.43

If used between buildings (probably using Parking Deck AC cable), it would be wired as any other method with an equipment ground conductor. Although I have never seen AC cable used for that type of installation.


250.84.
An equipment ground is not required for service entrance methods. If one should choose to use an armored cable type (such as MC cable) as permitted in 230.43, then you are not required to bond at the service equipment in the building/service location.
 
Mike, can you expand on the cable type at bit?
Is it actually AC cable as defined by Art 320, or are we perhaps talking about Art 328 MV cable, or jacketed MC, Art 330 ?

I;'m not familiar with an underground AC since AC is not approved for wet locations.
 
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I used the term Armored cable generically. The type of cable I am describing is multiconductor cable that has a steel wire-type armor contained within the jacket. I have ran into it quite often here in Iraq and Afghanistan and can only describe it as armored. It may go by another name. The cable is rated for direct burial. I want to determine whether or not this steel armor can be used as an EGC and if I do not intend to use the "armor" as an EGC what am I required to do with the armor at each end of the cable.
 
aslmost sounds like a jacketed MC cable in which case you can ingore the armor. If your connectors make contact with the armor (as opposed to the jacket) this would somewhat "gronnd" the jacket, but I lknow of no requiremt for it to be gronded. Of it's steel and escpecially interlocking, its a poor conductor anyway.
To give you a real "proper" answer, I think we would need to know exactly what type cable it is (AC? MC?, MV? MI? )
 
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