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600 amp service

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iwire

iwire

Moderator
Staff member
Location
Massachusetts
Re: 600 amp service

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.
Click to expand...
Explain to me how I go to one or more grounding electrode(s) individually only leaving the panel once.
 
B

bennie

Esteemed Member
Re: 600 amp service

The electrodes are individual until connected by one ground electrode conductor then they are bonded and become one electrode.
 
B

bennie

Esteemed Member
Re: 600 amp service

Bob: This is an often misread section. The text is saying that a ground electrode conductor can run to a ground system, which is already bonded.

The ground electrode conductor can also run to one or more individual electrodes when they are
not bonded.

The reason I know this even with the hard to understand wording, is that two earth connections will cause the current to ground, to divide according to the impedances(individually).
This creates a difference in potential at each electrode which produces noise on the grounding system.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Re: 600 amp service

Originally posted by bennie:
two earth connections will cause the current to ground, to divide according to the impedances(individually).
This creates a difference in potential at each electrode which produces noise on the grounding system.
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Bennie I have no reason doubt that. :)

However I still believe that I can leave the panel 6 times to go to 6 separate electrodes if I choose and meet the code.

Lets say I have 3 electrodes, water pipe, ground rod, ground ring.

Now if I run from the ground ring to the water pipe and from the ground rod to the water pipe and finally run from the water pipe to the panel I will have 3 individual grounding electrode conductors.

Your way or my way there is a plural amount of GECs
 
P

pierre

Senior Member
Location
Westchester County, New York
Re: 600 amp service

Bonding by NEC means 'the permanent joining', we do not use the dictionary definition for this case. Making multiple runs to the panel/disconnect and bonding there is permitted.

Jim
The wording in 250.66(A) may seem a little confusing at first, but it does work. If the CMPs were to try and word the code to work for different reading styles, it would never work, so they word it as best as each situation warrants - sometimes they do make mistakes. These days there are enough people who will let them know when the do ;)

The wording in 250.66(A) explains that the "'portion' that is the sole connection...", spells out that the ground rod if used with other electrodes or by itself is required to be connected with a 6 AWG conductor. It can be larger, but it is not necessary and in this case is a waste of conductor and money.

IMO - When a larger conductor is specified to a standard 8 foot groundrod, the specifier is either unsure of grounding sizing or doesn't understand the theory behind it.

Pierre
 
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jim sutton

Senior Member
Re: 600 amp service

Hello guys, its me again

this sure is a lively subject, to be so clear to everyone

first of all, I'm not an electrical engineer, and when I see a riser diagram drawn by an EE, I don't care to second guess him or argue with him about reducing the wire size to the ground rods.

The rods on these jobs are pretty much always 3- 3/4 x 10 ft copperclad placed in a triangular form.

I do my work in the most proffessional manner that I am capable of doing. As I am sure all of you do as well.

With all of the posts and the drawings, I see now how you all are reading 250-66(A). And I agree.

As I said in my first post, "the wording is strange" I think it needs to be changed.

But I guess I'm the only one who feels that way.

This dead horse is about beat!

We all know that faults return to the transformer through the grounded conductor.

So then the rods must be for lightning, correct?

Have any of you ever installed lightning protection systems? I was just wondering what size ground wire is used to the rods on these.

Thanks
 
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bennie

Esteemed Member
Re: 600 amp service

The NEC definition of the word bond is the same as accepted by the "Citation Readers" who determine the order of senses (definition) of the words. The citation readers are from all the publishers of dictionaries. The NEC has no citation readers.

An electrical bond is a low impedance connection between two conductive objects. An electrical bond therefore, has negligible resistance from one end to the other.

A ground electrode conductor, has measureable impedance therefore it is an inductor.

This statement is paraphrased from publications by the Electrical Engineering Department of the University of Pennsylvania.
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: 600 amp service

Bennie,
I don't understand. The same size and length of a GEC will have the same impedance no matter where it starts and stops.
Don
 
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bennie

Esteemed Member
Re: 600 amp service

Don: You are correct but multiple ground electrode conductors with multiple earth connections will have different impedance. This will produce a voltage difference at each point of connection. This is multi point grounding and can be dangerous in a fault or lightning strike.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Re: 600 amp service

Bennie I just do not understand how bonding them at the panel will be different from bonding all them at the water pipe.


3 grounding electrodes bonded at the water pipe will have 3 GECs each with their own impedance.

The same as 3 electrodes bonded at the panel will have 3 GECs each with their own impedance.

How is one better than the other and more to the point where in the NEC is bonding at the panel prohibited?
 
E

Ed MacLaren

Senior Member
Re: 600 amp service

The point is to create one path for current flow to earth.
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Why?

Both sketches illustrate "single-point" grounding, but A is better than B, in that the parallel GECs provide a lower impedance path to earth.

Multiple GECs also provide redundancy in the event of GEC physical damage - snow removal, vehicle collision, etc.

Service12.gif


Service13.gif


Ed
 
jxofaltrds

jxofaltrds

Inspector Mike®
Location
Mike P. Columbus Ohio
Occupation
ESI, PI, RBO
Re: 600 amp service

"Bennie I just do not understand how bonding them at the panel will be different from bonding all them at the water pipe."

Is Bennie saying that these would be in parallel?

Is that the point he is making?

I think I understand him, however I do not have the expertise to explain him.

Mike P.
 
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earlydean

Senior Member
Re: 600 amp service

Both diagrams meet code. Personal choice, job conditions, material at hand would determine which one we end up installing.
 
E

Ed MacLaren

Senior Member
Re: 600 amp service

This is multi point grounding and can be dangerous in a fault or lightning strike
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Let's try to clear up the controversy regarding the term "single-point grounding" once and for all.

My interpretation is -
the number of locations that the Grounding Electrode Conductor(s) connect to the system's grounded conductor.

I don't believe it means - the number of locations that the Grounding Electrode Conductor(s) connect to the earth.

Agreed or not?

Ed

[ January 02, 2004, 12:19 PM: Message edited by: Ed MacLaren ]
 
J

jim sutton

Senior Member
Re: 600 amp service

An electricians point of view:

Fault current will take the path of least resistance.

If the equipment grounds and the grounded conductor are properly bonded at the service, the fault would not go to the earth, it would travel thru the grounded conductor to the transformer, thru the windings and back to the overcurrent device and therefore trip the OC device.

The only way the fault could go to the earth is if the grounded conductor and the equipment grounds were not properly bonded.

I saw an illustration once where in the case of a fault where there was no grounded conductor, the fault current traveled thru the earth to the grounding electrode of the utlity transformer and then to the transformer windings back to the OC device.

It seems to me if you have multiple grounding electrodes with varying impedence, most of the fault would travel to the electrode with the least impedence with the remaining current going to the other electrodes based on there impedence.
If during the fault, a person contacted two electrodes with different impedences, he would be in series with the fault current. :(

On the other hand if they are all connected in series, this could not happen.

But of course ,either way meets code :D

[ January 02, 2004, 12:38 PM: Message edited by: jim sutton ]
 
B

bennie

Esteemed Member
Re: 600 amp service

The supply system must be connected to earth at only one location on the premises wiring system.

Two or more earth points is multi point grounding, regardless of the starting point. The ground/neutral bus does not bond anything. You can't bond at the source and create one ground electrode system. The bond conductor has to be at the connection point of all electrodes to the earth.

Multi point grounding of equipment is permitted, for ground fault purposes. Multi point grounding of equipment is permitted to a ground plane that has a low resistance. Multi point grounding of equipment to earth creates voltage gradients, noise, and equipment problems.
 
E

Ed MacLaren

Senior Member
Re: 600 amp service

The only way the fault could go to the earth is if the grounded conductor and the equipment grounds were not properly bonded.
Click to expand...
I think it is generally understood that the only types of "faults" the grounding electrode system has to "deal with" are lightning strikes, and accidental contact with the live conductors of other grounded systems, for example, a transformer winding-to-winding fault.

Ed
 
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bennie

Esteemed Member
Re: 600 amp service

Ed: Multi point grounding is when more than one connection is made to earth. The earth connections properly bonded constitute one ground point regardless of number of electrodes.

Multi point equipment grounding is when equipment is not connected to one common ground plate.

The ideal is to have all equipment ground conductors and the earth connection be made at the service only, and then to earth at one point.

This method prevents voltage gradients and common mode current flow in the system.

[ January 02, 2004, 01:18 PM: Message edited by: bennie ]
 
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jim sutton

Senior Member
Re: 600 amp service

Bennie,

So you are saying: take all of the grounding electrodes to one point, bond them all together with one GEC going to the service& grounded conductor?
 
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