grounding electrodes

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So if i have a service outside of a structure and from a panel [service panel] run rmc to a detatched structure for a sub panel will the rmc be accepted for a gec at the service or the subpanel or a egc to the subpanel or either.
 
electricalist said:
So if i have a service outside of a structure and from a panel [service panel] run rmc to a detatched structure for a sub panel will the rmc be accepted for a gec at the service or the subpanel or a egc to the subpanel or either.
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If you bury it to an 8' or greater depth somewhere along the way, sure it'll qualify as an electrode... :p

...otherwise, just an EGC.
 
Was there ever an exception that one could lay a ground rod horizontal if for some reason it couldnt be driven straight down,
If a water line isnt 8 ft. deep and qualifies why wouldnt rmc?
 
So does that qualify my nec to a garage as a gec....technically no I'm sure, but if it It will still do the job then underground rec conduits should qualify at 3'
 
electricalist said:
So does that qualify my nec to a garage as a gec....technically no I'm sure, but if it It will still do the job then underground rec conduits should qualify at 3'
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I suppose if you had rock bottom such that the requirements for placement were met, but I think there is another problem: There is new wording saying an EGC cant be a GEC (I am pretty sure on that but I cant find it right now). So does that mean you could if you had a wire EGC installed but not if you were using the RMC as the EGC?
 
electrofelon said:
I suppose if you had rock bottom such that the requirements for placement were met, but I think there is another problem: There is new wording saying an EGC cant be a GEC (I am pretty sure on that but I cant find it right now). So does that mean you could if you had a wire EGC installed but not if you were using the RMC as the EGC?
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That was added in 2011... but made less restrictive in 2014 (exception added).

250.121 Use of Equipment Grounding Conductors. An
equipment grounding conductor shall not be used as a
grounding electrode conductor.

Exception: A wire-type equipment grounding conductor installed
in compliance with 250.6(A) and the applicable requirements
for both the equipment grounding conductor
and the grounding electrode conductor in Parts II, III, and
VI of this article shall be permitted to serve as both an
equipment grounding conductor and a grounding electrode
conductor.
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However, there is nothing prohibiting the use of a conduit EGC as a GE.
 
Dennis Alwon said:
Yet a copper water line can be only 2' deep and still be an electrode.
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I think the assumption at the time those rules were written was that the metal water line was part of a metal water distribution system that could be several tens of feet long to miles long and likely connected to the electrical systems of many other services. :)

This is the same reason a metal water line requires a 'full size' GEC.
 
iwire said:
I think the assumption at the time those rules were written was that the metal water line was part of a metal water distribution system that could be several tens of feet long to miles long and likely connected to the electrical systems of many other services. :)

This is the same reason a metal water line requires a 'full size' GEC.
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I agree, but as you know that has changed. I am curious how a 20' run of rmc that is 6 or so inches below grade would compare to a 8' rod.
 
Denis I think you see where I was going with this.
I picked the better connection with RMC. Being threaded, the depth of an allowed electrode under exception as well as a electrode this is 2' deep as all being basically the same while taking no assumption as to what they thought the cold water was in depth or length.
For sure I wasn't after proving a point as much as learning.
 
250.52(A)(5) Rod and Pipe Electrodes - IMO means a rod or pipe used solely for the purpose of grounding elecrode.

There also is 250.52(A)(8) Other Local Metal Underground Systems or Structures. Which I see no reason why this can't include a RMC raceway undeground. This section as well as the following 250.53 doesn't really give any specific details of what requirements may be to use any electrode included in 250.52(A)(8), and I think you possibly find many inspectors may reject using a RMC raceway as an electrode because of lack of such details in the NEC - unless the raceway also met the general rod and pipe electrode requirements.
 
While reading my 2014 handbook I came across detached building and the egc requirements and thought. In the bigger picture if RMC was ran between them it could complete a bigger ges by offering a grounding electrode that bonds that at nearest entrance. With cold water going to RMC at sub panel.....
 
electricalist said:
While reading my 2014 handbook I came across detached building and the egc requirements and thought. In the bigger picture if RMC was ran between them it could complete a bigger ges by offering a grounding electrode that bonds that at nearest entrance. With cold water going to RMC at sub panel.....
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I believe you are correct. How much better of a GES is made, that can vary. 250.50 only requires electrodes mentioned in 250.52(A)(1) through (A)(7) to be used if they are present - a metal raceway would IMO be an (A)(8) electrode and is completely optional.

But 250.50 does also say if none of the electrodes in 250.52(A)(1) through (7) exist then one or more of (A)(4) through (A)(8) shall be used.

For most applications this usually means if there is a qualifying water pipe, building steel or CEE, you must use all of them that exist. The water pipe must have at least one other electrode type to back it up in case the water is ever converted to a non metallic system. If there is no water pipe, building steel or CEE present, then you must make at least one of (A)(1) through (A)(8) become present. Ground rods are the most popular to make become present because they are usually simplest and least cost. Rings, pipes (other then water), plates and other non mentioned electrodes usually have more design decisions behind the reason for their presence.
 
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