Ground conductor for MV line

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Salvador Santos

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Bahrain
Need some help on MV line installation. Our subcontractor have installed a 3x95mm.sq. Multicore Armored XLPE MV cable and have not included the ground conductor. When we have pointed out that they need to install the ground conductors, they have defended that the cable has it copper shield/screen and it will serve as the ground conductor. I'm not really clear if that will suffice as the ground conductor when in our design it must be 85mm.sq. wire.

Can somebody please provide a better explanation if the shield of the armored cable will suffice? My gut feeling says it won't.

Thanks
 
Yes, the shield can be utilized as the ground. It must be capable of carrying the fault current for the duration of time that it takes the protection to clear the circuit.

If you have access to the NEC, read Article 250.190, it is very informative in this regard.

If they say it is capable, than have them provide the calculation that shows that the insulation shield can handle the fault current. If they can't or won't, than a separate ground is required, and recommended.
 
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