PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

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davet

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PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECTRODE CONDUCTOR.

250.58 Common Grounding (Earthing) Electrode.Where a building or structure is supplied with multiple services or feeders as permitted by 225.30 and 230.2, the same electrode must be used to ground enclosures and equipment in or on that building.
In Pic 250-108 & Pic 250 - 109 Seems confusing according to the above statement because they are both the same pic.
If pic 250 - 109 creates this hazard ,than how can pic 250 - 108 be correct? and vise-versa.
Is there a safe way to get around this?

PS: I have the pics for this.It is on my desk top.I do not know how to insert these pics into my question,( exact typing )so they can see exactly what I am referring to.
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

He's referring to Mike's book Grounding Vs. Bonding page 54.
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

The first figure is simply showing you what is required to comply with the section. The second figure is simply describing the potential hazard of this requirement as stated in the Author's Comments.

There is no safe way around this rule as the code currently reads. I have submitted a propoasl for the 2008 NEC which I believe provides a means for identifying when the hazard exists.
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

To insert a picture, you have to post it on a web server, and then link to it.
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

Here is diagram 250.108.

:roll:

Roger
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

Remember the old rule: "A ground is a ground is a ground." At least, that's what the old-timers were taught.
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

Originally posted by bphgravity:
There is no safe way around this rule as the code currently reads. I have submitted a propoasl for the 2008 NEC which I believe provides a means for identifying when the hazard exists.
Click to expand...
Originally posted by roger:
Regardless of the commentary, I have never understood how the experts (including "Soars") can say ground loops are acceptable.
Click to expand...
Bryan and Roger I certainly agree with you both that the ground loops are an issue.

What I do not see is a good alternative. :(

If we could forget the NEC for a moment what would be an acceptable option for the installation below?

:(


Bob

[ February 05, 2006, 05:50 AM: Message edited by: iwire ]
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

I completely agree Bob. I didn't always, however Don and others convinced me of the real need for compliance with this section.

I have submitted a proposal that would require the use of an alarm system like that used to indicate a grounded phase of an ungrounded system. I don't have much confidence in its approval by the CMP, however I hope it spurs some commentary during the ROC that may lead to further development of better ideas.
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

Bob, I agree also and don't have a solution when dealing with multiple services.

Bryan, I do like your alarm proposal.

Where I think some improvement could be made is in 250.64(D) and it's allowing GE taps from multiple enclosures on one service. (especially if different sizes are in play)

;)

200-150.JPG


Roger
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

Originally posted by roger:
IMO the service grounding should be a single point.
Click to expand...
AMEM Brother. SPG would solve a multitude of problems
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

Thank You all for your replies.
Q. would grounding one of the xtrf.to a seperate ground rod create an additional hazard?
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

Thanks Dereck.

Dave, all services to one building would have to comply with part III of article 250 which would tie them together, and even with the problems that are present in doing so, it is the safest way.

Roger
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

Every electron that leaves the source, will return to that same source.

With this being said, how/why would the neutral current from the service on the left side of this building travel to the transformer on the right side of the building through the common GEC? I see two different sources here.


Maybe some would flow through the earth path between them, but that would seem to be miliamps.

[ February 05, 2006, 09:00 PM: Message edited by: pierre ]
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

Originally posted by pierre:
how/why would the neutral current from the service on the left side of this building travel to the transformer on the right side of the building through the common GEC?
Click to expand...
Plenty of current can travel as electricity takes all paths, not just the most direct path.


Originally posted by pierre:
Maybe some would flow through the earth path between them, but that would seem to be miliamps.
Click to expand...
It is not the earth I am concerned about, it is all the metallic paths between the two services, building steel, metal pipes, EGCs etc.

During normal operation the current will only be a small part of the unbalanced neutral current.

If the neutral on one of the services opens the current could be very high.
 
Re: PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECT

SPG would solve a multitude of problems.
Click to expand...
If we are going to do that, we shouldn't do it half way. The SPG should be at the utility transformer.
Don
 
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