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Old 02-23-2008, 07:01 AM   #1
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Sub Panel Grounding Question.


My inspector says all subpanels are to be 4 wired, isolated ground without a ground electrode at the subpanel. This is to insure that all grounding is common at the main. He will fail any subpanel with a ground electrode. This subject makes my head hurt.

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Old 02-23-2008, 07:28 AM   #2
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Sub Panel Grounding Question.


He is correct if the feeder is to a detached structure, although a "4-wire" feeder is not yet mandatory in NYS. It is always a good idea though.

Also, to say "all subpanels are to be 4 wired, isolated ground without a ground rod at the subpanel" is a stupid statement. If the sub-panel is within the same structure as the main panel NO additional ground rod is required or wanted.

Are you in Nassau, NY, or Nassau County?
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Old 02-23-2008, 07:36 AM   #3
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Sub Panel Grounding Question.


Sorry, I mean detatched Sub Pannel. This whole subpannel grounding thing is interesting, and confusing. My question is, what is the correct grounding procedure. Two ground electrodes in the ground are each a ground but they are not common to each other. If one was in a dry area, and the other in a wet area. If the 50 amp sub pannel has a better ground than the 200 amp service then it will try to cary the 200 amp ground.

Last edited by RobertS; 02-23-2008 at 04:04 PM. Reason: add to my confusion.
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Old 02-23-2008, 08:24 AM   #4
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Sub Panel Grounding Question.


Well, for one thing the "ground" does not carry anything. Just the purpose of a ground rod can be confusing. Let's just say they do not "do" very much at all.
They do NOT carry fault current, and they do not have anything to do with helping a breaker trip or preventing you from getting a shock.
A ground rod does NOT "provide" a ground. At least in the sense that most folks think a ground is, like the round pin on a receptacle.
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Old 02-23-2008, 08:27 AM   #5
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Sub Panel Grounding Question.


Like I said, it is not mandatory in NYS yet to run a 4-wire feeder to a detached structure, but we will be there someday because the NEC has already made this change.

What your inspector said is the correct procedure, but I am unclear as to what the heck he means by "This is to insure that all grounding is common at the main."
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Old 02-23-2008, 09:12 AM   #6
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Sub Panel Grounding Question.


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Like I said, it is not mandatory in NYS yet to run a 4-wire feeder to a detached structure, but we will be there someday because the NEC has already made this change.

What your inspector said is the correct procedure, but I am unclear as to what the heck he means by "This is to insure that all grounding is common at the main."
Now, I'm confused. I thought even with a four wire feeder, a ground rod was required at detached structures?
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Old 02-23-2008, 09:42 AM   #7
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Sub Panel Grounding Question.


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Originally Posted by Speedy Petey View Post
He is correct if the feeder is to a detached structure, although a "4-wire" feeder is not yet mandatory in NYS. It is always a good idea though.

Also, to say "all subpanels are to be 4 wired, isolated ground without a ground rod at the subpanel" is a stupid statement. If the sub-panel is within the same structure as the main panel NO additional ground rod is required or wanted.

Are you in Nassau, NY, or Nassau County?
Hang on Petey. Are you sure? A single branch circuit at a detached building doesn't require a grounding electrode, but a 4 wire feeder does See 250.32.

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Old 02-23-2008, 09:44 AM   #8
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Sub Panel Grounding Question.


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Here ya go... A 3-wire or a 4-wire feeder to an outbuilding would still require a grounding electrode, the one exception is a single branch circuit, or a multiwire branch circuit...
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Old 02-23-2008, 10:35 AM   #9
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Sub Panel Grounding Question.


OK, I never said a ground rod was not required at a detached structure fed by a FEEDER. I DID however misread the OP's quote of the inspector who said a rod is not required, and then said that I agree. I was wrong in that. If that makes sense.
I thought the OP's inspector said that a rod was required regardless of where the sub was. I see now he is saying no rod is required for a sub.
The inspector is WRONG, but I stand by my statements that a rod is not required if the sub is within the same building.

Also, Inphase, I am not saying a rod is not required yet, I am saying a 4-wire feeder is not yet mandatory in NYS.

I'm sorry guys. I do see that I messed this whole thread up by misreading the OP.
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Old 02-23-2008, 12:44 PM   #10
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Sub Panel Grounding Question.


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Originally Posted by Robert Shields View Post
My inspector says all subpanels are to be 4 wired, isolated ground without a ground rod at the subpanel. This is to insure that all grounding is common at the main. He will fail any subpanel with a ground rod. This subject makes my head hurt.
well, how about this to throw a little fun in the works.

a ground rod is NEVER mandatory. Period.

Petey? I know you know what I am stating here.
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Old 02-23-2008, 01:11 PM   #11
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Sub Panel Grounding Question.


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well, how about this to throw a little fun in the works.

a ground rod is NEVER mandatory. Period.

Petey? I know you know what I am stating here.
Please elaborate. If you have a metal water line as an electrode, you must supplement it with some other type of electrode. True it doesn't have to be a rod, pipe or plate. It can be the ufer ground or building steel, or ground ring.

As a side, I started using the ufer ground in place of rods on all my services. Well, in one county near Atlanta, the inspector turned me down because he couldn't find the rods (I wasn't on site when he came). When I met him for re-inspection, I told him I didn't use any rods and that we had a water pipe electrode and a ufer. "In my jurisdiction, services got to have driven rods too". I asked him why, he just glared at me and asked me if I wanted to pass the inspection. He said "It's like when your wife calls you on your way home and tells you to get a gallon of milk. You just do it. If I say put a rod, you just do it."

I could have stabbed him with a screw driver, I was boiling. But we got over it. I drove the rods.

But please do explain what you mean , nap.

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Old 02-23-2008, 01:34 PM   #12
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Sub Panel Grounding Question.


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Please elaborate. If you have a metal water line as an electrode, you must supplement it with some other type of electrode. True it doesn't have to be a rod, pipe or plate. It can be the ufer ground or building steel, or ground ring.


But please do explain what you mean , nap.

InPhase277
You got the point. A rod is not a mandatory grounding electrode. There are always alternatives and a supplemental electrode is often not requried.

code requires all electrodes included here (of course if they are within the defined specs of the code):

underground waterpipe

metal frame of building

concrete encased electrode (Ufer is of this type)

ground ring

rod & pipe electrodes

plate electrodes.

Any of them on site MUST be utilized BUT it does not require that any of them be installed. It also does not require any supplemental electrodes if ANY of them are present other than the water pipe electrode.

So no rod is ever required. You are correct in your installation of the ufer and water pipe. Considering many water pipes are now plastic, the ufer alone is acceptable if that is all of the "included list" above that is present.

I actually had an inspector question me as to why I had actually even driven rods in a commercial install. Said I did not need them. Also told me that one rod was adequate in any part of his jurisdiction without test as every test (in all the various locations) had far surpassed the 25 ohm requirement and accepted 1 as adequate due to those tests. I would not have other than the job specs required it.
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Old 02-23-2008, 01:41 PM   #13
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Sub Panel Grounding Question.


but I digress;

as to the original question; I never saw if the panels in question were within the same builiding or in outbuildings.

If within the same building then the inspect is correct. No electrodes for the sub-panel.

If in outbuildings then inspect is wrong (considering he intended rods to mean any acceptable electrode) as they are always required for an outbuilding.
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Old 02-23-2008, 01:56 PM   #14
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Sub Panel Grounding Question.


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Well, for one thing the "ground" does not carry anything. Just the purpose of a ground rod can be confusing. Let's just say they do not "do" very much at all.
They do NOT carry fault current, and they do not have anything to do with helping a breaker trip or preventing you from getting a shock.
A ground rod does NOT "provide" a ground. At least in the sense that most folks think a ground is, like the round pin on a receptacle.
What planet are you on??
From article 100 Definitions: Grounded effectively:"Intentionaly connected to earth through a ground connection of sufficently low impeadence and having sufficient current carrying capicity to prevent the buildup of voltages that may result in undue hazards to equipment or to people."
Please enlighten me if I have missed something.
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Old 02-23-2008, 02:04 PM   #15
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Sub Panel Grounding Question.


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What planet are you on??
From article 100 Definitions: Grounded effectively:"Intentionaly connected to earth through a ground connection of sufficently low impeadence and having sufficient current carrying capicity to prevent the buildup of voltages that may result in undue hazards to equipment or to people."
Please enlighten me if I have missed something.
That means static, lightning, and high voltage line crossings. The Earth is not the path for fault current at line voltage.

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