GEC returned to panel

[tjmicsak]

I have seen this requirement in a few local Utility service installation books, and was asked to do so by an inspector. I had to run the GEC from the panel, to rod 1, to rod 2 and then back into the panel, basicaly doubling the GEC, and creating one GEC for each rod, but all tied together. I think this is not NEC and feel one GEC to rods 1, then 2 unbroken is all that is called for. So why do they ask for this "return loop"?

 

[physis]

Re: GEC returned to panel

It's not NEC and you'd have to ask your AHJ.

It doesn't even have to be continuous after the first electrode.

250.64(F)

Ask him to read it. It's only one paragraph.

 

[george t. everett]

Re: GEC returned to panel

In my area, the Poco requires a separate run to each rod. If one lead gets cut you will still have the other. Not required by code, but not a bad idea.

 

[charlie]

Re: GEC returned to panel

George, you get that with a loop also but, in my opinion, the electric utility has overstepped their bounds.

 

[physis]

Re: GEC returned to panel

I should have mentioned there might be local requirements.

 

[john m. caloggero]

Re: GEC returned to panel

George: Having a separate grounding electode conductor run out to each grounding electrode creates a problem. Because the rods are at some distance apart, circulating currents develop when there is any leakage current. Also when there is a high voltage cross-over or a lightning strike, a potential difference will develop betweent the two ground rods. A single grounding electrode conductor should be installed to the closest ground rod and the second ground rod must be bonded to the first one by a bonding conductor or a continuation of the grounding electorode conductor.

 

[physis]

Re: GEC returned to panel

I was thinking there could be adverse conditions created by two GEC's. I'm not so sure about that if it's a loop and there electrically connected.

 

[hurk27]

Re: GEC returned to panel

By John: Having a separate grounding electrode conductor run out to each grounding electrode creates a problem. Because the rods are at some distance apart, circulating currents develop when there is any leakage current. Also when there is a high voltage cross-over or a lightning strike, a potential difference will develop between the two ground rods. A single grounding electrode conductor should be installed to the closest ground rod and the second ground rod must be bonded to the first one by a bonding conductor or a continuation of the grounding electrode conductor.

I'm not following this very well. I would agree if the source of this voltage was from two different locations placing the rods in between the two sources. Like one rod connected connected from one service drop and the other connected from a second service drop.( which is why we must bond all grounding electrodes together in the first place 250.50) or in a case where a service is close to a utility pole like in a city where many services are located close to an alley where also the utility poles are located you could have a voltage difference between the rod at the utility pole and the rod at the service. But the two rods connected to the same point at the same service by two GEC's would not seem to be able to have a difference of voltage if the source of this current is from the opposite side of the service and would have to pass through this common connection point to get to the rod's?

A very common grounding method for lightning protection is using this very concept, multiple connections to Earth to drain off the lightning voltage more efficiently. This is done with radials or just multiple grounding points all connected to a single point at the main service or just outside the building to a single grounding bar.
I could see a far more greater potential for this in the NEC (250.64(F)) where it is allowed to bond grounding electrodes to other electrodes like in the case of bonding a rod electrode to the metal building frame just because they are in series with each other, a lightning strike could put a difference of voltage potential at each electrode because of the voltage drop of each GEC in series with each electrode.

 

[physis]

Re: GEC returned to panel

By Wayne:

I could see a far more greater potential for this in the NEC (250.64(F)) where it is allowed to bond grounding electrodes to other electrodes like in the case of bonding a rod electrode to the metal building frame just because they are in series with each other, a lightning strike could put a difference of voltage potential at each electrode because of the voltage drop of each GEC in series with each electrode.

Do you mean that you're concerned about the connections at the electrodes or using something in the electrode system as a bonding jumprer?

 

[hurk27]

Re: GEC returned to panel

Sam what I was trying to say is when two ground rods are connected each by it's own GEC to the main service disconnect it will connect to a single point that will be at "0" resistance or close to it at that point between the two GEC's, A lightning strike anywhere on the system would have to pass through this point to go to the rod's thus eliminating any voltage difference between the two. Each will share the current to earth. Unless there is a great length of run difference between the EGC's running to the rods, in which the rod's would be to far apart to touch both anyways. And a single rod would pose just as much of a touch hazard in the event a person was touching it at the time lightning were to strike. Or the system had a contact with a higher voltage. I was trying to show that a rod in series with the building steal would have a greater chance of having a voltage difference on it because of the resistance of the building steel. 250.64(F) allows the installation that John said "creates a problem"

250.64(F) To Electrode(s). A grounding electrode conductor shall be permitted to be run to any convenient grounding electrode available in the grounding electrode system or to one or more grounding electrode(s) individually . The grounding electrode conductor shall be sized for the largest grounding electrode conductor required among all the electrodes connected to it

[ November 29, 2004, 02:23 AM: Message edited by: hurk27 ]