4.17kV Switchgear High Resistance Grounded Working Space

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WastefulMiser

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How is an HRG accounted for in nominal voltage to ground.

Is it simply:

4.17kV to ground

or

4.17kV / sqrt(3) to ground = less than 2500V

So in a Condition 2 instance would it be four or five feet of working space required in front of the switchgear? I believe five feet is minimum and I am making sure that is correct.
 
WastefulMiser said:
How is an HRG accounted for in nominal voltage to ground.

Is it simply:

4.17kV to ground

or

4.17kV / sqrt(3) to ground = less than 2500V

So in a Condition 2 instance would it be four or five feet of working space required in front of the switchgear? I believe five feet is minimum and I am making sure that is correct.
Click to expand...

4.17kV / sqrt(3) to ground = less than 2500V
Condition 2 would be 4 feet.
 
WastefulMiser said:
Correct me if I am wrong, but when a phase becomes grounded then the other two phases will read L-L when grounded. Thus 4.17kV to ground.

Yes, no? 4 feet? 5 feet?
Click to expand...

You are correct. When a phase is grounded the other two phases will be 4.17KV to ground. That should be an abnormal situation and I would still consider the nominal system voltage to be less then 2500V to ground. I could be wrong but that is how we see it. Don't you have ground fault relays set to trip in the event of a ground fault? That is standard for MV installations where I work.
 
eric9822 said:
You are correct. When a phase is grounded the other two phases will be 4.17KV to ground. That should be an abnormal situation and I would still consider the nominal system voltage to be less then 2500V to ground. I could be wrong but that is how we see it. Don't you have ground fault relays set to trip in the event of a ground fault? That is standard for MV installations where I work.
Click to expand...

I am not the end user so it depends on customer to customer on whether to set to trip when a ground fault occurs.

I have been setting the switchgear at five/ six (cond. 3) feet; however, one day I may not have room in a building and was curious if four feet/ five (cond. 3) was acceptable, and if not, I will have a justifiable reason to ask for an increase in the building size.
 
eric9822, thank you for your comment on the matter. Any one else care to comment on the code requirements in this senario?

Would it all depend upon the AHJ?

What would you do?
 
That should be an abnormal situation and I would still consider the nominal system voltage to be less then 2500V to ground.
Click to expand...

I have to agree with Eric, since the definition of "Voltage, Nominal" per NEC 100 is "a nominal value assigned toa circuit or system for the purpose of conveniently designating its voltage class..." so I would think a similar definition is the intention of the Code. IF a fault happens as described in the previous posts and there's no ground fault protection (or it fails) then you may have an arc flash situation, in which case the extra foot wouldn't do you much good.
 
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