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#170104 - 10/26/07 11:12 AM Ground rod required at subpanel?
mxslick Offline
Member

Registered: 10/24/04
Posts: 785
Loc: Atomic City, ID USA
Thought I'd throw this out to the gurus here for a final answer....first the detail of the install:

200amp meter/main panel located at pump house. Two ground rods and well casing tied to ground bus in this main panel. Passed inspection no problems.

100 amp feeder to subpanel, with ground wire, all THHW/THHN, in PVC conduit to said subpanel in main house. Ground bus and neutral bus isolated at subpanel as per Code. Run of about 110 feet.

We do have telco and (most likely not to be used) CATV run from the pumphouse to the main house. Again in PVC conduit.

Inspector wants us to drive a ground rod at the subpanel location in the main house.

I feel that it would not be required, as the grounding of the system is established at the main service. If, for example, we had only a meter socket/can at the pump house, with the main panel being at the house (where the EGCs and neutral would be bonded, right?) would we require another ground rod. Adding the rod is not a problem, the walls are unfinished at this stage.

I am also concerned about creating a separate ground fault path...something rattles in the back of my mind about this rod being necessary only if another grounding path exists between the buildings...

Not too sure of what Code section (art. 250 of course) this would fall under, inspector did NOT give a Code reference.

This is in So. Cali., (up in the fire zone) and we're under the 2005 Code.

Thanks!!
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#170105 - 10/26/07 11:26 AM Re: Ground rod required at subpanel? [Re: mxslick]
Yoopersup Offline
Member

Registered: 03/04/03
Posts: 826
Loc: Michigan
You need a Grounding Electroid system per 250.32 installed in accordance with 250.50 even if you run a equipment ground. If the buildings are not tied together.(one Building).
The NFPA nec Code handbook spells this out quite well in. 250.32
Neutral floats in SubPanel. Grounds Equipment and Electroid system tie together.

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#170113 - 10/26/07 05:47 PM Re: Ground rod required at subpanel? [Re: Yoopersup]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5299
Loc: Blue Collar Country
The inspector is just a bit ahead of his time ....

If there are no metal paths between the two buildings, the code can be read to say that no ground rod is required. This ambiguity, though, will go away in the 08 code .... where it is said to make clear that detached buildings do need ground rods.

Code finesse aside, though ... that ground rod is there for lightning (more than anything else). It's sure not there to clear faults. It seems only sensible that anything that might make a separate 'target' for lightning have its' own rod.

EVEN WITH a rod, though, I'd keep the neutral and ground separated at this panel. Can't say why ... it just seems right that way.

NOTE: I'M WRONG .... corrected post later on ... OOPS!!!


Edited by renosteinke (10/27/07 11:08 AM)

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#170114 - 10/26/07 05:54 PM Re: Ground rod required at subpanel? [Re: renosteinke]
Yoopersup Offline
Member

Registered: 03/04/03
Posts: 826
Loc: Michigan
A grounding electroid system IS required whether or Not you bring 3 or 4 wires even in 2005 code. Neutrals and Ground are required to be bonded together if by code you are allowed to run 3 (no equipment gr.)Required to be seperate if you run four.
Theres only one Exception 250.32 A exception

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#170115 - 10/26/07 06:34 PM Re: Ground rod required at subpanel? [Re: Yoopersup]
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
Ernie- You've never been more right in your life. See Ya in Rochester, you can buy me an adult beverage:)
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#170122 - 10/26/07 11:50 PM Re: Ground rod required at subpanel? [Re: renosteinke]
mxslick Offline
Member

Registered: 10/24/04
Posts: 785
Loc: Atomic City, ID USA
(Bold emphasis in the following quote added by me..)

 Originally Posted By: renosteinke
The inspector is just a bit ahead of his time ....

If there are no metal paths between the two buildings, the code can be read to say that no ground rod is required. This ambiguity, though, will go away in the 08 code .... where it is said to make clear that detached buildings do need ground rods.

Code finesse aside, though ... that ground rod is there for lightning (more than anything else). It's sure not there to clear faults. It seems only sensible that anything that might make a separate 'target' for lightning have its' own rod.

EVEN WITH a rod, though, I'd keep the neutral and ground separated at this panel. Can't say why ... it just seems right that way.


Thanks, Reno. That confirms what I had thought, i.e. the '05 and earlier Codes are not too clear on this requirement. That was what gave me pause when we got this notification.

And being as this is a remote area somewhat, I agree that lightning protection is a good reason for that extra rod.

I intend to keep the neutrals and grounds separate at the subpanel....now if that inspector had instructed us to bond the neutrals and grounds at the subpanel that would have brought out my claws. \:\)

And to be clear, I will be adding the rod, it wasn't an issue of doing it (I'm all for going above what Code asks for) but I was concerned about the duplicate grounding paths possibly being an issue.

Oh yeah, this cabin is being built by my friend (who's an inspector himself) and wired by both of us. He was as surprised as I was by this request from the local AHJ. \:\)

Yooupersup, thanks for the Code article references too. Are those from '05 or the upcoming '08?
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#170124 - 10/27/07 03:10 AM Re: Ground rod required at subpanel? [Re: mxslick]
Fred Offline
Member

Registered: 04/30/01
Posts: 461
Loc: Straughn, IN 47387
Reno is mistaken and your inspector is correct. 2005 NEC article 250.50, "Grounding Electrode System. All grounding electrodes as described in 250.52(A)(1) through (A)(6)that are present at each building or structure served shall be bonded together to form the grounding electrode system. WHERE NONE OF THESE GROUNDING ELECTRODES EXIST, ONE OR MORE OF THE GROUNDING ELECTRODES SPECIFIED IN 250.52(A)(4) THROUGH (A)(7)SHALL BE INSTALLED AND USED." I believe that is quite clear. 250.52(A)(4) through (A)(7) does not list the 4th wire(EGC) of the feeder as a grounding electrode.

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#170125 - 10/27/07 05:52 AM Re: Ground rod required at subpanel? [Re: Fred]
Yoopersup Offline
Member

Registered: 03/04/03
Posts: 826
Loc: Michigan
The section 250.32 I quoted is from the 2005. Its the same in the 2008 except they added in the exception: (including a multi wire banch circuit)instead of as in 2005(for the purpose of this section, a multiwire branch circuit shall be considered as a single branch circuit).

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#170128 - 10/27/07 08:23 AM Re: Ground rod required at subpanel? [Re: Yoopersup]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
The question that gets asked is if the telco is a "metal path" and the question becomes, did you reground the telco at the second building? That still only refers to the 3 wire feeder (regrounded neutral) vs 4 wire feeder (separated neutral). Our buddy Ryan made that moot with his proposal to the 2008.
I am going to be curious to see how this works out in lightning country. There is going to be a significant difference between grounds and neutrals in interconnected equipment at the far end. This may require different thinking in the surge protection of some equipment.
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#170130 - 10/27/07 09:13 AM Re: Ground rod required at subpanel? [Re: gfretwell]
Roger Offline
Member

Registered: 05/18/02
Posts: 1779
Loc: N.C.
The coax sheild is a path connecting both buildings so a four wire feeder would be necessary.

Regardless of a four wire or three wire feeder, Ernie is correct.

If a three wire feeder is used, the sub-panel rod will be connected as if it were a service GE, and if a four wire feeder were used, the GE would connect only to the sub-panel enclosure and EGC in the feeder.

Roger

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