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 Post subject: Medium Voltage "exposed"
PostPosted: Mon Jan 30, 2012 8:30 pm 
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The surface of insulation in medium voltage wiring is not necessarily actually "ground" or near ground. This is even more so with unshielded conductors for CPT leads in enclosures and the like, never mind shielded conductors.

So going strictly by 70E standards, medium voltage conductors would be considered "insulated". However this fails the intent as obviously the idea is that the surface of the insulation is under 50 volts.

So with medium voltage conductors, a shock hazard can be present even if insulated.

Has anyone else considered how to handle this? Is there something in a standard somewhere to address it?


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PostPosted: Tue Jan 31, 2012 3:42 pm 
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Treat unshielded MV cables the same as bare. I don't know if there are any code restrictions, but for safety sake, do it.


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PostPosted: Tue Jan 31, 2012 8:47 pm 
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And shielded? From the cable manufacturers it looks like the shielding simply stabilizes the voltage stress. It has nothing to do with reducing voltage potential on the cable sheath.


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PostPosted: Wed Feb 01, 2012 11:56 am 
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NFPA 70E Table 1.30.7(C)(15)(a) requires rubber insulated gloves for 1 kV throuth 38 kV insulated cable examination. The table does not distinguish between shielded and unshielded.

In most cases, the shield is grounded. If it is not grounded at the point of examination, there could be voltage induced in the shield by current in the conductor.


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