Grounding meter stacks

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kenman215

Senior Member
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albany, ny
Just wanted to double check the grounding on this install:

1200A OCPD feeding a bus style terminal cabinet. 4 buses, 3 hots and a neutral. Ground is separate in the TC, bonding jumper not being used due to the fact that it's after the breaker. So I have 4 pipes that my feeders pass through into the TC, each with a set of 500MCM AL with a 250 ground. In total, I have 4 250 MCM grounds that attach to the cabinet, and this pathway is carried through the stack via 2 1/4-20 bolts. I believe this install to be code compliant, but the fact that the 50 meters downstream share the same 1/4-20 ground path just doesn't feel right in my gut.

Opinions?
 
Smart $

Smart $

Esteemed Member
Location
Ohio
Is the 1200A OCPD the service disconnecting means?

Is it in the same cabinet as the bus connections... or is all in a switchgear-, MCC-type configuration with multiple section of same equipment. Your thread title vs. question is contradictory, misleading at worst.

Also, I don't believe you are allowed to double up grounding terminations (which are different than splices but the distinction can be vague).... I'd have to look it up to verify.
 
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kenman215

Senior Member
Location
albany, ny
Smart $ said:
Is the 1200A OCPD the service disconnecting means?

Is it in the same cabinet as the bus connections... or is all in a switchgear-, MCC-type configuration with multiple section of same equipment. Your thread title vs. question is contradictory, misleading at worst.

Also, I don't believe you are allowed to double up grounding terminations (which are different than splices but the distinction can be vague).... I'd have to look it up to verify.
Click to expand...

1200A beaker in the main switchboard feeds a terminal cabinet. Bolted on to that are ten sections of meter rack, each with 5 meters and 5 125A breakers. Not sure where the contradiction came in. I have meter racks and want to double check the grounding. Where did I suggest doubling up grounding terminations?
 
Smart $

Smart $

Esteemed Member
Location
Ohio
kenman215 said:
1200A beaker in the main switchboard feeds a terminal cabinet. Bolted on to that are ten sections of meter rack, each with 5 meters and 5 125A breakers. Not sure where the contradiction came in. I have meter racks and want to double check the grounding. Where did I suggest doubling up grounding terminations?
Click to expand...
Here...
kenman215 said:
...I have 4 pipes...
...I have 4 250 MCM grounds that attach to the cabinet, and this pathway is carried through the stack via 2 1/4-20 bolts.
Click to expand...
 
Smart $

Smart $

Esteemed Member
Location
Ohio
kenman215 said:
1200A beaker in the main switchboard feeds a terminal cabinet. Bolted on to that are ten sections of meter rack, each with 5 meters and 5 125A breakers. Not sure where the contradiction came in. I have meter racks and want to double check the grounding. Where did I suggest doubling up grounding terminations?
Click to expand...
How are the 1200A breaker and the bus-style terminal cabinet connected???

Again, is the 1200A breaker the service disconnecting means.
 
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kenman215

Senior Member
Location
albany, ny
Smart $ said:
How are the 1200A breaker and the bus-style terminal cabinet connected???

Again, is the 1200A breaker the service disconnecting means.
Click to expand...

1200A breaker is the service disconnecting means from the main switchboard. There are wires that terminate at the breaker, that then travel through pipes and attach to lugs that are attached to bus bars in the terminal cabinet. Those bus bars attach to bus bars in each 5 meter section of the stack. The cabinet comes with 1 ground lug, whose hole accommodates 1 250MCM AL.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
kenman215 said:
Still don't see how that is a contradiction between the thread title and question I asked. Still seems like I'm talking about grounding a meter stack as the title would imply...
Click to expand...
In bus-terminal cabinet: 1) two grounding studs, and 3) four grounding wires (actually five if one is run with the feeder, but I'll give you the benefit of the doubt and say it uses a different bolt and lug). That means you have to double up on both or triple up on one as I'm imagining it. Perhaps you can explain away my imagination... such as using two-conductor mechanical lugs.

BTW. I'm not certain it's totally required to have distinctly separate terminations... but I seem to recall there's a requirement that grounding conductors must be installed so you can remove any one without interfering with others. Someone will correct me if I'm wrong. I'm being lazy right now, or I'd look it up myself.


And I'm still wondering about the lug hole size. The stud or bolt size vs. lug hole sie is not a Code requirement. It may be a listing requirement, i.e. 110.3(B).
 
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kenman215

Senior Member
Location
albany, ny
You're uncertainty is not warranted and your recollection is correct. Grounds are sized for the breaker, not quartered off like the parallel feeders.

I said in a previous post that the grounds are attached to the cabinet. It's my failure for not elaborating that although there is only one grounding lug, the other three are separately purchased mechanical lugs attached to the cabinet via Tech 4 drill point screws, whose thread pattern is code compliant for a mechanical grounding means. How to attach the other three was never the problem.

My issue, what doesn't feel right in my gut, is that the ground path from one section of the stack to the other, all the way back to the TC is accomplished through the two 1/4 20 bolts and star washers (thanks for that) that are used to mechanically attach each section to the next.

Hopefully this clarifies what I was talking about. If not, I'm throwing in the towel.

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Smart $

Smart $

Esteemed Member
Location
Ohio
kenman215 said:
...
Hopefully this clarifies what I was talking about. If not, I'm throwing in the towel.
Click to expand...
If I understand you correctly, each meter stack section bus bars connect directly to the bus bars in the terminals cabinet (typically this requires "jumper" bars, but I'll let that fly for now). The terminal cabinet is mechanically attached by way of two 1/4-20 bolt w/nuts, washers per meter stack section. The grounding conductor lugs (except one?) are not bonded to the cabinet via the bolts mentioned in the last sentence. There are no wire-type grounding conductors from the terminal cabinet to the meter stack sections. Correct so far? If no, please elaborate where I am wrong.

If yes, is the terminal cabinet and meter sections sold as compatible sections by the same manufacturer, and simply assembled in the field? ...or is the terminal cabinet custom shop made? If manufactured and sold as a field assembled unit, is the assembly or the terminal cabinet a listed accessory... or something like that?

Are there any bolts securing section to section?


It sounds like you are aware of Code to a degree, but I must say I do not believe there is any "approved" means to correctly terminate a 250kcmil EGC using a tech screw, or several, even if they have machine-thread.... and I believe most other patrons here will agree with me. And this concerns me more than the two bolts per section you are concerned with.
 
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kenman215

Senior Member
Location
albany, ny
You're close. All sections, are made by the same manufacturer with interlocking bus bar sections, so you don't need any jumpers, just have to tighten one 3/8" nut per section of bus.

The 1/4 20s with star washers are what secure section to section. There are machine threaded receivers formed into one side of the section. On the opposite side of the section are simply just 5/16" drilled factory holes, which is what the 1/4 20s pass through to thread into their receiver counterparts, and is also why, I'm assuming, the star washers are necessary, so that they scrape the painted metal.

There is no grounding bus, neither in the TC, nor the meter sections. What does exist in the meter sections is a small ground bar that is bonded to the bottom of the cabinet, where the grounds of the SER'S are terminated. The only metal to metal contact is through the 1/4 20s attaching the meter sections together. They are 3R rated, so there is a gasket between both cutouts where the bussing connects, so there isn't even incidental contact.

The TC ships with with only a single mechanical grounding lug, which is bonded to the metal enclosure via a 10-24 or 10-32 machine screw. You have to add lugs to accommodate more than 1 ground, in this case 4 of them. I don't believe that there is anything in the code about what screws to use for this purpose other then a minimum gauge or I might be possibly confusing it with a listing for the Tech 4s. Either way, the additional mechanical lugs tend to sit tighter then the factory installed ones.

My issue is, as I stated before, is what kind of path could the 1/4 20s with star washers possibly provide?

When you look at the required ground conductor size coming in and what passes for a ground path by the manufacturer, it seems like we're putting monster truck tires on a smart car...


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Smart $

Smart $

Esteemed Member
Location
Ohio
kenman215 said:
...
My issue is, as I stated before, is what kind of path could the 1/4 20s with star washers possibly provide?
Click to expand...
Well if you think the 1/4-20's are insufficient as bonding jumpers, there is nothing in Code to prevent you from increasing or enhancing the effective grounding path. I can't imagine the manufacturer only provides for two 1/4-20 bolts per section. If it were my design, it'd have at least four, if not six per section.


Yet I find this all ironic, coming from the person that uses tek screws to bond 250kcmil EGC'c to a cabinet. :slaphead:
 
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kenman215

Senior Member
Location
albany, ny
Smart $ said:
Well if you think the 1/4-20's are insufficient as bonding jumpers, there is nothing in Code to prevent you from increasing or enhancing the effective grounding path. I can't imagine the manufacturer only provides for two 1/4-20 bolts per section. If it were my design, it'd have at least four, if not six per section.


Yet I find this all ironic, coming from the person that uses tek screws to bond 250kcmil EGC'c to a cabinet. :slaphead:
Click to expand...

The TCs factory 250 lug is attached via an 8-32 machine screw, which is listed and approved for this purpose. The Tech4 screws that we use have a drill point, followed by a very ironic 10-32 thread. Thus the screw choice...
 
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