adding ground conductor

[sparky]

I have a customer reguest to install additional ground conductor at his dairy farm. The reguest was from a Stray Voltage expert advise. The building is feed under ground in direct buriel cable with 2 phase conducters and 1 grounded(neutral) conductor 120/240 single phase feeding from a main panel on another building. He would like me to install the new ground conductor over head and jump from building to building attaching this ground conductor to each panel and isolating the neutral and ground connection with a ground bar. Opinion ? :

 

[charlie]

Re: adding ground conductor

300.3(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (4).

Emphasis mine.

 

[kendog]

Re: adding ground conductor

Just my opinion but I would strongly you recommed that he run it underground with the rest of the wires. I'm not a hundred percent sure what article it is but I remember reading that conductors of the same circuit must be the same length. Feel free to correct me if I'm wrong though been a while since a read that.

 

[jtester]

Re: adding ground conductor

sparky
Charlie is right, any conductor used as a ground in a circuit must be run with the phase wires. In your case, someone may be telling you to treat symptoms instead of causes.The expert that you mentioned may have looked for the cause of the stray voltage, but in my experience, many times someone talks to the farmer and tells him to run more ground wires. This often makes things worse. Someone should be sure the farmer got good advice first.
Your description has many possible classic sources of stray voltage.
1. Ground faults, either a branch circuit failing or in your case a direct buried feeder, are probably the most common sources of on-farm stray voltage. There are step by step methods for tracking down the problems.
2. Imbalance putting excessive current on the neutral. Assuming that at each building the neutral is bonded to ground and if it has significant current on it, some will travel thru the parallel ground paths. Cows are roughly 10x as sensitive as humans to perceiving voltage, and only a little current will spoil their day.
There are other on-farm sources, as well as off-farm sources. I have seen a couple of Mike Holt e-mails on stray voltage recently. There is other information on the internet as well.
There is no substitute for identifying the source of the stray voltage and correcting it.
Jim T

 

[dillon3c]

Re: adding ground conductor

Charlie# 59.Just wondering, Could Shocker just install another "Site-Isolating Device"547.9 & 547.9(b)(1)remote from the first,Providing his feeder conductors are sized right,check and see if he can follow all the conditions of 250.32(b)and, follow though with the requirements are far as equipotential plains and insulated grounding conductors where needed as far as equipment,to said second remote Isolating device,and still meet the requirements of the NEC?

 

[sparky]

Re: adding ground conductor

I thought that something didnt seem right about this reguest. Does any one have a opinion on the reason am sure Iwill be ask? and saying its against code doesnt mean anything to farmers. I know parallel conductors must be the same length to be sure amprage is split egually.

 

[jtester]

Re: adding ground conductor

sparky
I suspect that some non-electrical guy will tell you or the farmer that this will work even though it might not be "Code". I have seen literally hundreds of feet of copper wire run around a dairy to eliminate stray voltages, and it didn't help a bit. When properly installed your ground will be a circuit conductor, and must be grouped with the other wires.
We recognize that a wire has impedance in AC, resistance and reactance. When you install that wire in a circuit, there is a circuit impedance that becomes involved. This impedance is based, in part, on the spacing between wires. The greater the spacing the more the impedance. Power people are used to this concept because their wire spacing varies often.
In the case of a remotely installed ground, the ground fault circuit impedance increases greatly, and could limit fault currents to the point that OCPD's would not work.
It is a significant safety issue and in spite of what the farmer tells you, don't do it.
Jim T

 

[petersonra]

Re: adding ground conductor

I am sick of these so called experts who blame things on "bad" grounds, yet do not know enough that they suggest something forbidden by code.

I'm not real sure how adding an EGC would help anyway, since there is already a neutral running out to the panel and presumably that is earthed at the outbuilding.

It could be helpful to try and bond all the metal building parts to the panel ground bar in each of the outbuildings, as this could reduce any potential difference between earth and metal building parts that the crittres might be feeling. It might even help to make sure the ground rod at the outbuilding is adequate, maybe even adding one on the opposite side of the building (the probability of this being helpful is very low if the existing ground rod is properly installed, but its possible its not or it could be stuck in some soil that is poorly conductive I suppose). But I don't see how just running an EGC out there will solve anything.

 

[petersonra]

Re: adding ground conductor

Originally posted by sparky:
I know parallel conductors must be the same length to be sure amprage is split egually.

This is not a paralell conductor situation since the EGC is not carrying any current. Its still suppsoed to be run with the current carrying conductors though.

 

[jtester]

Re: adding ground conductor

quote
I don't know how adding an EGC would help anyway, since...
I believe that an EGC would help if there is much load imbalance at the time of milking. Since the neutral, without a separate EGC, would be bonded to ground at each building, earth is a parallel path for neutral currents. These areas have dirt that is often much more conductive than we are used to, and only a little current will bother a cow.
Isolating neutral and ground at each outbuilding, and moving the neutral-ground connection, if necessary, away from the first building will limit or eliminate current flow using earth as a neutral path.
I would encourage sparky to track some information down if he wants to truly help the farmer. There are publications available, mostly in dairy areas, to provide instructions on how to help identify the source of stray voltages and to reduce them. I have publications from the University of Minnesota and from Texas A&M, I'm sure there are others.
Jim T

 

[highkvoltage]

Re: adding ground conductor

If it is a seperate building and has a subpanel why not just install a ground rod at that location. It there is no subpanel install one where the wires enter the building then install the ground rod. Also I would have everything GFCI protect due to moisture. Bond everything according to the NEC.

 

[charlie]

Re: adding ground conductor

One of the things we have found is that so much wiring is cobbled up by the handy man that the system just needs to be cleaned up. After everything is grounded so it is Code compliant, then see if they still have a stray voltage problem.

By the way, the grounding problems don't have to be in the same building as the perceived problem.