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Cables 100 or 133% insulation

Cables 100 or 133% insulation

Cables 100 or 133% insulation

(OP)
Hello all,

I would like to know if:

There is any normativity to use cable insulation in electrical systems of 460, 480 V. (low voltage)
The neutral system currently is solidly grounded and there are plans to install a neutral resistance to limit single phase to ground faults currents, however, as temporary overvoltages may happen, we do not know if there are some code requirements to use some insulation of 100 or 133%.

As far as I have read on NEC, 133 and 173 % insulation level only is applicable to medium voltage cables.

Any help or comments will be welcome!
 

RE: Cables 100 or 133% insulation

Cables for 480V are at least rated for 600V, which is a 25-30% margin anyway, so I do not think it matters for LV systems. It is not a code requirement that I know of.

Yes, 100%/133% is typically for MV systems.
 

Rafiq Bulsara
http://www.srengineersct.com

RE: Cables 100 or 133% insulation

With a grounded wye your cable insulation will be exposed to 277 Volts to ground. When you go to resistance grounding your insulation may be exposed to 480 Volts during ground faults. If you are buying cable approved North America it will be 600 Volt rated. If you look closely at the cables they may be 1000 Volt rated. 600 Volt cables and 1000 Volt cables are often used interchangeably in Canada.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Cables 100 or 133% insulation

When you have high resistance grounding the ground fault current is limited to 5-10A. Therefore, the faulted phase voltage never goes to zero thus not imposing an over voltage on the remaining two phases.

As it was said before, cables in North America are rated for 600V (1000V is usually used in Canada as the rated voltage is 600V). Therefore, there is no issue using 600V cables for 480V system.

What you have to make sure that you have ground fault indication as this is a code requirement.

For more info on high resistance grounding you can check out www.i-gard.com.

Regards,

Zsolt

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