480 Equipment ground

[iwire]

Re: 480 Equipment ground

Originally posted by don_resqcapt19:
]And these same electricians that don't know about ungrounded systems would understand a corner grounded delta system????
Don

Don honestly I am one of those electricians who is not very familiar with either system.

I do not see how working with corner ground delta is all that different from working with a Wye system.

I would make my measurements to ground and find the grounded conductor.

I do imagine working with an ungrounded system will be entirely different, the need for monitoring etc.

I would not be expecting an ungrounded system and try to make measurements to ground that would be confusing and most likely meaningless.

If I am wrong correct me and I will learn something new.

 

[augie47]

Re: 480 Equipment ground

corner grounded are rare in this area, but ungrounded is very common. I think Bob is correct, it does require a bit of training to work these. In addition bonding is, of course, extremely important.

 

[tom baker]

Re: 480 Equipment ground

"One is not inherently more dangerous than the other", this is not entirely true.
An ungrounded 480 v system can create overvoltages up to 2200 volts in a arcing ground fault (this information is from Mike Holts 2005 GvB material).
This creates tremendous stress on the wiring.
However one option is to use an impedance grounded system, which combines the wye system advantages with the ungrounded system advantages (reliability)

 

[don_resqcapt19]

Re: 480 Equipment ground

Bob,

I do not see how working with corner ground delta is all that different from working with a Wye system.

The problem that most electricians have with the corner grounded system is that one of the phase conductors has zero volts to ground. They don't expect this and think that there is a problem. Also, even though the code requires this conductor to be identified as grounded conductor, I have never seen that happen in the field.
Don

 

[jim dungar]

Re: 480 Equipment ground

Tom,

Actually 2200V is a conservative figure for a voltage level during an arcing fault on an ungrounded 480V system. I did not say the system was without problems. But a properly installed and maintained ungrounded system is not inherently more dangerous than a grounded one. An incorrectly installed and maintained system is dangerous even if it is grounded. And it can be a completely different discussion for delta versus wye.

And I agree do not use systems that are drastically uncommon in your geographic area. But, in my area (200mi radius) I cannot think of a voltage system that I have not seen at least once in my career, including 120V delta ungrounded.