Can resistance grounding be used legally with MV - say 4160V?

Mike, in Fig. 1, I think the arrow for #Bonding Wire" is incorrectly pointing to the grounded neutral.

K Cassidy

Figure 1 on page 2 of " A Guide to High Resistance Grounding Part 1 of 4: Power System Grounding Basics" shows bonding of the neutral in the transformer and in the service entrance switchgear. This might lead one to believe that the neutral to ground bonding conductor is required to be installed in both places.I think that they may be showing this to illustrate it can be done in either place. If that is the intent it is not clear. I think they may have to add a note to Figure 1 to clear this up.

Part 1.1 states "Grounding Conductors do not carry ground fault current." Is this correct?

In the article recently sent out by Mike titled "Equipotential Planes, A Figment of the Imagination", there is a quote from EPRI which states "40 - 60% of the neutral return current ... returns to the source substation through and/or over the earth" Doesn't this mean current must pass thru the Grounding Conductors, into the ground, then back to the source?

Your 2nd paragraph has a big mistake in it.

I would like to see a copy of the "National Electric Code". I have never been able to find this code. You probably meant to reference the National Electrical Code. BIG DIFFERENCE! One of them doesn't exist and the other one does. A jury would have a field day with a reference to the first, especially since it doesn't exist.

The old lamppst dos not have a grounding.Can help isolation transformer only? Yes. Why? No.Why?

There are some Cahier Techniques papers on this subject over at Group Schneider's website that specify different and much more robust ratings for grounding resistors and transformers.

These documents are:

ect062.pdf neutral earthing techniques

ect190.pdf ferroresonance

Possibly also ect181.pdt directional protection

One of these documents recommends that the available current from the neutral grounding resistor be at least 2 times charging current, twice as much as the I-gard people recommend.

A resistor that is on the secondary of a wye primary broken 120 volt delta secondary should be rated for continuous use at 360 volts, not the 208 volts that I-gard recommends.

MY recommendation is that a neutral grounding resistor and any grounding transformer has to withstand what happens when there is a power cross between the resistance grounded system and the next lower voltage such as 120 volt control power. This can happenvery easily if somebody is troubleshooting using a jumper wire or if a forklift truck shears off a power feed that contains say 480 volts resistance grounded and 120 volt auxiliary power. A zero phase shift ( delta primary zig-zag secondary ) transformer creates the most amount of voltage across a neutral grounding resistor when a power cross occurs.

MY opinion is that the primary windings of a wye primary broken delta secondary transformer should be rated 600 volts on a 480 volt resistance grounded system. In this case a power cross to 120 volts from a more common delta primary wye secondary transformer could put 600 volts across one of the grounding transformer primary windings. Obviously, we would want the transformer to handle this without saturation until protective relays or manual action removes the fault.

This is just a difference in opinion between different electrical engineers as to what values are required.

Michael R. Cole, mc5w at earthlink dot net