Having received no replies to my request to review the thread, I would like to repost the original question. Readers, please note that there are two locations referenced here- a "main disconnect" and a "main panel." Both are currently grounded via driven ground rods but only the main disconnect has a bonded neutral. I would much appreciate some of the experts in this group responding to the questions herein.


I apologize that my original question was not perfectly clear. I am also well aware that the problems were caused by the failed neutral but in the process of replacing the "main" breaker panel I wanted to reevaluate my grounding system and upgrade it if advisable. Let's start over.

A main fused, 200A disconnect is fed via underground cable ( the one which failed). This disconnect is grounded via a driven rod. The first question is whether I should consider upgrading this ground by running a ground to a well casing which I will be able to do when the power company fixes their underground cable? (neutral bonded at this disconnect).

When originally installed, the main breaker panel in the house was fed with about 60'-70' of 3-wire service entrance cable run underground from the main disconnect. I believe this to have been a mistake as no ground was provided. Instead, a second ground rod was driven in a different location to ground this panel. Finally, when I constructed a garage, I ran a conduit between the main disconnect and the breaker panel. At present, there is #6 ground conductor in this conduit.

My electrician feels this ground conductor should not be used. If I wish to improve the ground at the main panel, he advises only driving a second ground rod. So this is the second question. Should I tie the main disconnect and main breaker panel grounds together with the #6 conductor or leave the breaker panel grounded only via the driven ground? If tying them together is a good idea, should I pull something larger in the conduit (#4?)? (reminder, neutral is not bonded in this panel as per code).

I believe it is true that using the ground in the conduit is actually a code violation because it is not "contiguous" with the conductors in the 3-wire cable. My goal is only to get the best ground possible.

I appreciate the significant knowledge of stanfortaman in his posts. My understanding is that grounding systems are primarily for safety purposes but at higher frequencies (above 60Hz) may also provide for signal references and lightning protection. In any case, I believe NEC requires grounds and, hopefully, with a low impedance to "earth ground." I am much less clear on the actual aspects of providing good grounds and it is not clear to me whether "better grounds" might have alleviated some of the wild voltage swings resulting from the neutral failure.

This post is long and complicated, so for now I'm going to look at these paragrphs:

Quote:

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Originally Posted by jpsbach

A main fused, 200A disconnect is fed via underground cable ( the one which failed). This disconnect is grounded via a driven rod. The first question is whether I should consider upgrading this ground by running a ground to a well casing which I will be able to do when the power company fixes their underground cable? (neutral bonded at this disconnect).

When originally installed, the main breaker panel in the house was fed with about 60'-70' of 3-wire service entrance cable run underground from the main disconnect. I believe this to have been a mistake as no ground was provided. Instead, a second ground rod was driven in a different location to ground this panel. Finally, when I constructed a garage, I ran a conduit between the main disconnect and the breaker panel. At present, there is #6 ground conductor in this conduit.

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I don't believe a well casing can be used as a ground rod, but it can be "grounded" as part of the equipotential bonding. Multiple ground rods can be sunk per NEC rules, but the ground must be continuous and have a minimum spacing.

If copper, It should be 3/0 and #4 wire for ground. Ground should be insulated.

It should be a 4 wire system. The size of the Neutral may be able to be reduced. The main panel should be treated as a sub-panel with independent grounds and neutrals. It does not have to be a main-lug panel.

The garage should be 4 wire as well. It only needs a ground rod if it is considered a detached structure.

Comments so far?

Quote:

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Originally Posted by jpsbach

I believe it is true that using the ground in the conduit is actually a code violation because it is not "contiguous" with the conductors in the 3-wire cable. My goal is only to get the best ground possible.

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Explain "non contiguous"?

One piece from disconnect to main panel is correct. A separate cable within the conduit is fine.

It appears I still generate confusion but will try to avoid. Wiring the garage is not part of the question as it is appropriately fed with 4 wires from the main disconnect. The problem is that the house is being fed with only 3 wires and the ground I keep asking about is running in its own conduit from the main disconnect to the panel in the house. Presently the ground in the house is ONLY a driven ground. The ground running through the conduit is not connected. Should I connect this? If so, the panel in the house would have two grounds, one from the main disconnect and a separate driven ground.

Best ground

The best ground is no ground loops and the least amount of ground resistance. Actual resistance can be measured. So can ground resistivity. Thus multiple ground rods connected to the disconnect and verifying the resistance is the ONLY way to achieve that.

Equipotential bonding
Gas, water line and pool bonding need to be carried out correctly.

Best ground

The primary purpose is for lightning strikes and a reference.
In Hospitals and computer facilities there can be two ground busses that are used. They both would start at the place where the neutral is connected to the ground rod.

One would be "protective ground" and would be green.
The other would be "independent ground", "Isolated ground" or "Signal ground" and would be green with yellow stripe. Sensitive equipment would use this ground. There is no need to go that far.

Example:
Machine shop would use the green.
Network servers/CATV the green/yellow. Orange colored outlets would be used in this case too.

Where is the "main disconnect"?

Attached to the house?
Attached to the garage?
Attached to a pole or separate structure?

Quote:

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Originally Posted by jpsbach

It appears I still generate confusion but will try to avoid. Wiring the garage is not part of the question as it is appropriately fed with 4 wires from the main disconnect. The problem is that the house is being fed with only 3 wires and the ground I keep asking about is running in its own conduit from the main disconnect to the panel in the house. Presently the ground in the house is ONLY a driven ground. The ground running through the conduit is not connected. Should I connect this? If so, the panel in the house would have two grounds, one from the main disconnect and a separate driven ground.

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Being wired this way would have contributed to many problems.

The house panel should be 4-wire fed. The ground be made independent at the main panel.
The ground rod connection does not have to be there UNLESS the main disconnect is detached (residing in/on a different structure) from the main panel location.

Ok, I certainly understand improving the ground at the main disconnect. I can do that by driving additional rods and/or running a ground to the well casing.

This still leaves the ground at the panel in the house as a problem. Should I remove the existing ground to the driven rod and use only the ground running back to the main disconnect (perhaps upgrading to a larger size)? Should I use both or will this potentially create a ground loop? Is there any easy way to measure whether one has a ground loop?

A larger ground can never hurt. It just costs more.

A reminder that ground should only take hits from fault currents and provide a reference voltage for some communications such as CATV and USB periferals, for example.

If your scared and don't want it to happen again. You can purchase a product like the RCM420 here: BENDER Inc. - Products - Ground Fault Monitors for Grounded Systems

Which will keep tabs on ground faults.

Multiple ground rods probably won't have an effect on anything except giving greater lightning protection from lightning strikes.

Ground currents can be measured with sensitive clamp on meters (around 30 mA full scale) placed around the conductor to ground.

I would still like to clarify the situation regarding the feed from the main disconnect to the main panel.

The main disconnect is in an attached garage but there is no easy way at present to change the existing 3-wire feed from there to the house panel. I do have this conduit running between the two.

Do I understand correctly that I would be better off if I abandoned the ground at the house panel which is an independent driven ground (not the one at the main disconnect) and used the ground running from the main disconnect to the house panel. Or should I just use both?

I thought you said you have the following between the main disconnect and the main panel:

Line 1
Line 2
Neutral
#6 ground, currently not used

Main disconnect Ground rod
House Panel - Ground rod
Neutral and Ground independent at the house Panel

I hope I'm seeing this right.

Am I seeing something like a meter base and an independent disconnect feeding two panels?

Am I seeing the garage panel being the "main panel/disconnect" and the "house panel" being a sub-panel and fed from the "garage panel"?

Or an external house mounted disconnect, feeding a "main panel" in the garage and that panel feeding the "house" panel.

Or something else?

There isn't just one way that's correct possibly because codes have changed.

In old work, you can have 3 wire feeds. Ground and neutral will be connected together in this case in the "house" panel. The neutral would run between panels. Ordinarily, the ground rod would not be used because the structure is attached to the structure containing the "main disconnect".

I don't have time right now to think about this too much but I will say that the well casing should not be used as a grounding electrode. In addition to it not being recognized as an acceptable electrode by the NEC it very well may already, and should if one exists, be connected to the equipment grounding conductor for a submersible pump circuit. Of course I don't know if you even have a submersible pump but either way it's not an acceptable electrode and could create a ground loop.