35kV grounding conductor question

[reko19]

We have an underground feeder with 35kV cable. For whatever reason contractor decided to use 600V green cable as a grounding conductor. Our design drawings call for everything to be 35kV, but since equipment grounding conductor does not really have to be insulated and could be bare (this clearly used as equipment grounding conductor not as a neutral) would this installation be acceptable?

Thank you.

 

[dbeasley488]

35kv grounding with 600V insulated cable

35kv grounding with 600V insulated cable

I don't see any reason not to OK it. EC must have had it in stock from another job and needed to use it somewhere.

 

[reko19]

I don't see any reason not to OK it. EC must have had it in stock from another job and needed to use it somewhere.

this is exactly the reason, was easier for EC to get it. I as well don't see a reason, just want to make sure I am not missing anything.

 

[roger]

A 600 volt insulation level is all that is needed, and as stated, it could even be bare.

See 250.184

Roger

 

[jdsmith]

We have an underground feeder with 35kV cable. For whatever reason contractor decided to use 600V green cable as a grounding conductor. Our design drawings call for everything to be 35kV, but since equipment grounding conductor does not really have to be insulated and could be bare (this clearly used as equipment grounding conductor not as a neutral) would this installation be acceptable?

Thank you.

We design our 35 kV feeders with a 600V green THWN wire just the way the contractor installed yours. A bare grounding conductor is acceptable per code, but in the event of a fault you would get sparking between the ground and the tray or conduit, so we prefer insulated grounding conductors.

 

[dbuckley]

In the event of a 35KV fault to the ground conductor you'll probably still get sparking as the insulation gets punctured by serious overvoltage.

Assuming solid grounding and the ground and phase condutors are the same cross sectional area and thus the same impedence (which isn't the case but bear with me a mo), at the point where the short occurs the point of the short will be at half the line voltage, and the line voltage will depend on the supply impedence, but could well be well above 600V.

Typically the ground conductor is of lesser cross-sectional area than the phase conductor, so the bolt point wont be half the supply voltage, but higher, as the voltages will divide as per the impedence of the phase and neutral conductor.

So I'm less than convinced that insulation breakdown wont occur.