Section 250.58 Common Grounding Electrode

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bphgravity

Senior Member
Location
Florida
New text (bold print):

Where an ac system is connected to a grounding electrode in or at a building or structure, the same electrode shall be used to ground conductor enclosures and equipment in or on that building or structure. Where separate services, feeders, or branch circuits supply a building and are required to be connected to a grounding electrode(s), the same grounding electrode(s) shall be used if the requirement of (1) is met.

(1) An audible or visible alarm shall be installed at each service to indicate the grounded conductor brought to the service has opened.

Exception No. 1: In industrial installations, with written safety procedures, where conditions of maintenance and supervision ensure that only qualified persons service the equipment.

Exception No. 2: Where electric service and electrical maintenance are provided by the building management and where these are under continuous building management supervision.


Substantiation: Upon the opening of the grounded (neutral) conductor at one service, potentially dangerous current will flow between the common electrode to both services. Any person who comes in contact with exposed metal parts at the service equipment or grounding electrode system could be exposed to lethal current.
 

charlie

Senior Member
Location
Indianapolis
Re: Section 250.58 Common Grounding Electrode

When you use if you now have to give an alternate method for the if you don't situation. The implication is that you do not have to use the same grounding electrode.

The second thing is that you have started a list but only have one item in the list, that is a violation of the NEC Style Manual. :D
 

bphgravity

Senior Member
Location
Florida
Re: Section 250.58 Common Grounding Electrode

I knew the wording wouldn't be right, but I was just trying to get the spirit of the proposal across.

Revised Text: ...the same grounding electrode(s) shall be used and an approved audible or visible alarm shall be installed at each service to indicate the grounded conductor brought to the servie has opened.

Exception In industrial installations, etc.... or where electric service and, etc.... the approved audible or visible alarm shall not be required.
 

charlie

Senior Member
Location
Indianapolis
Re: Section 250.58 Common Grounding Electrode

OK Bryan, I think it will probably work. :D

I am not too sure that I like the idea of spending mega-bucks on this device though. How much trouble do we really have with open grounds to be worth the expense? :confused:
 

ryan_618

Senior Member
Re: Section 250.58 Common Grounding Electrode

I think you might have to gather some facts about people getting injured and/or killed in order to get this type of proposal to pass. Think of how many people have tried to eliminate the code allowance of multiwire brach circuits? Each cycle there are proposals to delete 210.4 by several people, and there are several good arguments towards it, and many public comments towards it, but it all comes down to showing the CMP some dead bodies to prove the need for it.

For example:
Submitter: Craig M. Wellman , Newark, DE
Recommendation:
Replace all existing text in Section 210.4 with the following:
210.4 Multiwire branch circuits. Multiwire branch circuits shall not be permitted. A circuit serving a single utilization appliance or
machine with both line-to-line and line-to-neutral loads and having a single disconnecting device that opens all ungrounded
conductors shall be permitted.
Substantiation:
Multiwire branch circuits have long been permitted, but it is time to recognize that these circuits are a hazard and should not be used.
When maintenance is being performed and the neutral or grounded conductor is opened, line voltage is present if all ungrounded
conductors have not been disconnected. It is often impossible to identify the circuits that must be disconnected in advance. Many
people do not understand the hazard involved and even those who do are forced to do live work, which they rightly fear. It is widely
recognized that many people have been killed or injured when they contacted the neutral in a multiwire circuit. It is common for an
injury to occur when someone is knocked off a ladder by the shock.
Recognize that the purpose of the code is the practical safeguarding of persons and property from the hazards arising from the use of
electricity. While the code has contributed greatly to reducing injuries, injuries still occur and future progress will require changes in
the code. This change may be hard to accept because the practice is so common and so long standing, but only a change to the code
requirements can eliminate this hazard in new installations.
Panel Meeting Action: Reject
Panel Statement:
The substantiation provided is of a general nature and does not sufficiently establish that a safety problem exists for qualified service
and maintenance personnel who are trained to work with and properly troubleshoot multiwire branch circuits. The proposal would not
reduce the potential shock hazard to unqualified personnel who endeavor to work on panelboards or utilization equipment where
multiwire branch circuits are present.

Number Eligible to Vote: 13
Affirmative: 11 Negative: 2 Ballot Results:
Explanation of Negative:
MARSHALL: This proposal should be accepted. It would be a relatively simple fix to a variety of problems. Foremost is the dangerous
condition presented by "hot neutrals" when not all of the circuits in the multiwire system are disconnected. Lost neutrals in such
systems can impose 240 volts across 120 volt equipment. It would also eliminate the problems created by high harmonic neutral
currents.
ROCHE: See my Explanation of Negative Vote on Proposal 2-14.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Re: Section 250.58 Common Grounding Electrode

I'd echo Charlie and Ryan's comments on this one. I just wish I thought Ryan were 100% correct on "the facts" that are necessary to support a Proposal. Unfortunately, I believe several CMPs have accepted Proposals that were not economically justified.

Section 90.1(A) says the NEC is to be a "practical" standard. That means "$" are also supposed to be a consideration. A clear line can always be drawn between "safe" and "unsafe." "Unsafe" simply isn't permitted. In my opinion, where a Proposal suggests that an installation that the NEC already considers "safe" can be made "safer," any increase in the Proposal's financial costs, should be specifically justified.
 

peter d

Senior Member
Location
New England
Re: Section 250.58 Common Grounding Electrode

Slight threadjack.

I find it mind boggling that anyone would introduce proposals to ban multiwire circuits. It makes no sense to me. OK, I can understand the copper and conduit industries trying to do it, but their motives would be a lot clearer.

I think I am going to write a proposal banning circuits all together. After all, you can get shocked by using electricity, so it's best that we just don't use any circuits, in case any unqualified or untrained people try to work on them live.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Re: Section 250.58 Common Grounding Electrode

One of the things we all have to look at is how safe can we afford to be? Its "obvious" that anything can be made safer, all the way to the ridiculous example of doing away with electricity all together. But even in that example its entirely likely that using kerosene lamps would end up being far more dangerous than the electric circuits they replace.

Its also very true that there is a certain amount of trade off between safety and dollars. It might well be true that there is some incremental improvement in safety by eliminating the use of NM cable in favor of rigid, but the incremental improvement in safety would be dwarfed by the added cost.

I know some would say "if even one human life was saved..." to justify any expense in the pursuit of safety, but someone has to draw a line in the sand somewhere and say this is as safe as we need to be. The code making panels and UL people by and large do a pretty fair job of doing this.
 
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