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#94047 - 07/04/05 05:12 PM Supplemental grounding electrodes  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
I'm posting this from a Telecom newsgroup for the original author. I've already made a few comments of my own (copied below), but I'm hoping ECN's code experts might be able to pull up some more references that might be applicable, or at least throw in some thoughts and comments.

Quote
Ten years ago I happened to discover a potential of 0.25 VAC between the grounding electrode under my electrical entrance and the one under my telephone entrance. To protect my computer from lightning, I bonded them with twenty feet of wire. It paid off in 1998 when lightning struck a tree thirty feet from my electrical entrance. I was online and suffered no damage.

A telco man restored service by replacing a fuse on the utility pole. When I asked the company's policy on bonding, he beat around the bush twenty minutes before saying the electrical code required it but the telco didn't like it because they would have to replace more fuses.

Neighbors went online five years ago. Each time they've lost a modem or surge protector, they have asked me for an explanation and I've told them ground surges will keep getting them until they clamp a wire between their phone and power electrodes. They have always ignored my advice.

I was online Monday during a quiet rain when lightning hit my chimney, blowing masonry and shingles sixty feet in all directions. My screen froze with a weird tint, but things were fine when I restarted.

My neighbors weren't so lucky. Their phone electrode is 40 yards from my chimney. Their power electrode is 10 yards farther. They lost a modem, a satellite dish, and two telephones. Instead of demanding that I explain it again, they asked the telco to send a rep. He told them their ground is fine. My neighbors are pleased because this proves I have always been wrong.

Article 250.54 of the NEC says local supplemental grounding electrodes (such as the one for phone service) must be bonded to the primary electrode. Where does the NEC apply?

According to what the telco man admitted seven years ago, I assume our county code says the same thing.

Is this a recent addition to the NEC? How is a citizen supposed to find out local code requirements? How is a citizen supposed to know his electrodes are not bonded or that it's necessary? If the telco assures a customer that there is nothing wrong with grounding which in fact is a code violation, does the telco have any liability?



My response:

Quote
As I understand it the NEC applies in any state, county or local jurisdiction which has adopted it -- which is most. There may be local codes which explicitly amend any NEC requirement though.

Which edition of the NEC are you looking at? In the 2002 edition article 250.54 relates to supplementary electrodes which MAY be bonded,not MUST. 250.58 does seem to correspond with 250.54 in earlier editions though, so that could be the section you are looking at.

Chapter 8 of the NEC also relates specifically to communication systems. Article 800.40(D) in the 2002 edition states:

Bonding of Electrodes. A bonding jumper not smaller than 6 AWG copper or equivalent shall be connected between the communications grounding electrode and power grounding electrode system at the building or structure served where separate electrodes are used.



>Is this a recent addition to the NEC?


No. I don't know how far back the requirement goes, but the 1971 NEC says much the same thing in article 800-31(b)(7):


Bonding of Electrodes. A bond not smaller than No. 6 copper or equivalent shall be placed between the communication and power grounding electrodes where the requirements of (5) above result in the use of separate electrodes.


I did explain that being in the U.K. I'm far from an NEC expert. So any thoughts on this?

I'll provide the original author with a link to this thread so that he can see any responses directly.


[This message has been edited by pauluk (edited 07-04-2005).]


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#94048 - 07/04/05 06:39 PM Re: Supplemental grounding electrodes  
Ryan_J  Offline
Moderator
Joined: Aug 2003
Posts: 1,374
West Jordan, Utah, USA
250.54 is not the correct reference. 250.54 applies only to electrodes that are not required to be installed, such as optional electrodes that you might find in a lighting pole, or for a piece of equipment. The NEC recognizes the fact these electrodes do little if anything at all, and therefore 250.54 states that there are no sizing, routing or temination provisions to be complied with.

The electrodes being discussed here, however, are in fact required to be installed, and therefore they muist be installed in a code compliant manner. Becasue 90.3 considers chapter 8 to be a stand alone code, Article 250 is not to be referred to at all, unless something in chapter 8 tells you to refer to Article 250.

The installation you seem to be concerned with is communications, and therefore Article 800 needs to be examined. We start with section 800.100(B)(1) of the 2005 edition which requires that communications system not only be earth grounded, but that it must be bonded to the power system grounding electrode system, in accordance with 800.100(B)(1), or the other components listed in that subsection, which will ultimatley ensure that the power system and phone system are both grounded to the same location. Such grounding conductor must be less than 20 feet in length. If this can't be done, you are required to drive a ground rod at least 5' deep, then tie the new ground rod to the pwoer grounding system, again, as discussed in 800.100(B)(1).

although the various service providers never comply with thee requirements, you can find the same requirements for other limited energy circuits, such as coaxial cables for CATV, satelite installations and for network powered broadband systems. This should help your equipment from geting wiped out.

If this doesn't make sense, let me know Paul or original author.

Perhaps you might even get lucky and have an expert reply to this thread!

[This message has been edited by Ryan_J (edited 07-04-2005).]


Ryan Jackson,
Salt Lake City

#94049 - 07/04/05 11:44 PM Re: Supplemental grounding electrodes  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,126
Estero,Fl,usa
I backed into the electrical business from the computer biz. I spent a lot of years on the bleeding edge of lightning protection in South Florida where we have a thunderstorm almost every day for about half the year.
The first thing we did was establish a "star" wired grounding system where all electrodes on the property got bonded to the center of the star.
If you give transients a more attractive path through equipment you are going to lose that equipment.
The answer is bonding with fat wire, shunting with things like MOVs and delaying with ferrites. You want layers of protection but you need a good common ground reference to build on.


Greg Fretwell

#94050 - 07/08/05 12:55 PM Re: Supplemental grounding electrodes  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Quote
250.54 applies only to electrodes that are not required to be installed, such as optional electrodes that you might find in a lighting pole,

That's how I read it as well, but wanted to check with those more familiar with the code. Thanks.



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