Single family dwelling with a 200 amp service from the utility located at the dwelling, service disconnecting means and overcurrent protection located at dwelling.

Property has a seperate horse barn out back.

If I install a underground 4-wire single phase feeder in PVC to the horse barn from the dwelling, is the equipment grounding conductor of the 4-wire feeder required to be:

1) The same size as the ungrounded supply conductors?

2) Insulated or covered copper only?

I'm using the 2005 NEC as a guide and the new part (C) of 547.9 seems to allow the standard sizing requirements of table 250.122 to apply to the equipment grounding conductor of a 4-wire feeder to the barn as described above.

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I do not believe that you are applying the code correctly.

If you are running but two circuits- a single multi-wire branch circuit- then the chart you reference would be appropriate.
If your intent is to feed a panel, I believe that 250.66 is the appropriate chart, and the ground wire would need to be at least #8. You could actually be -depending on the size of the feed- in the goofy situation where the ground has to be larger than the neutral!

This "fourth wire" can be either insulated and marked green, or bare copper wire. It must be inside the raceway.

While your application may be simple today, there are enough other issues around the farm- stray voltage, other equipment, moisture, waste, animal damage, corrosive chemicals, etc- that I see little profit in taking advantage of any "short cuts."
You didn't ask, but if you did, I would say "Dig- and dig deep." I'd urge the use of pipe- either RMC or sched 80 PVC. I'd remind you to have a disdonnect on the outside of the barn. And I'd reccomend that everything, even inside the barn, be NEMA-3R or, better yet, NEMA-4 Too many little critters get into the electric as it is!

My approach is conservative- mostly learned in Chicago- but it has served me well in these days of "power quality" issues.

Thanks renosteinke...My mistake,I should read the book a little slower next time...

Section 547.9 has been revised and restructured for 2005 and had me confused early this morning


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Reno, why isn't this a 250.122 "equipment grounding conductor"? You are not dealing with service conductors. This is on the load side of the service disconnect. The feeder conductors, by definition, are protected by an overcurrent device.

Testing....

Sorry for not answering sooner, gfretwell. Looking at the references to feeders in section 250, you are sent on a "white elephant hunt" through the code, that ultimately leads to a different table.

This can lead to some interesting situations, such as, in theory, where the code will allow the neutral to be smaller than any other wire, while at the same time requiring the ground to be larger than the hot wires! (While I've never seen this in the real world, the possibility is there....)
250 has been improved considerably in the past few cycles, but still has a looooong way to go :-)

My original question came from reading 547.9(B)(3)(b)(1) which states the equipment grounding conductor (where installed) has to be the same size as the largest supply conductor. But this applies to OVERHEAD conductors with a seperate EGC.

Underground feeders with a EGC would send us to table 250.122 for proper sizing of the EGC...

Also, any equipment grounding conductor installed underground in a 547 building must be insulated or covered

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547.9 (D)
Where livestock is housed, any portion of a direct buried EGC run to the building or structure SHALL be INSULATED or COVERED copper.

Caps are not for shouting

Charlie