Duplex and connecting to GEC

[George Stolz]

However, after further review, I would say this installation is legal, based on 250.58.
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I would say you could omit the conductor between Unit #2's panel and the GEC, as it is not required.

I am by no means 100% confident of my answer to this question, so any responses (yea or nay) are welcome. I figured I'd give this thread a bump this morning, looks like some folks cleverer than I are on at the moment.

 

[flick]

I'd say your service conductors are in violation of 310.15 - I would say that you cannot use Table 310.15(B)(6) for the sizing of the service conductors (on the line side of the meters) because they do not serve an individual dwelling unit, they serve more than one dwelling unit. The conductors on the load side could use the Table, but the line side ones should technically be sized greater than the calculated service load, using Table 310.16.

I'd call it a minor violation, because if left to their own devices, the utility would likely have installed conductors smaller than that anyway.

I am also curious about your routing for the service entrance conductors between the meters and the panels. Are they through the slab?

(Not trying to pick on you, I've learned I had some bad habits before folks here pointed them out to me. )

The SE conductors into the meter can are 4/0 aluminum. Calculated load is 60A in one duplex, and 65 in the other. Smallish 2 bedroom units, gas furnaces, gas water heaters, A/C each side. I don't have the calcs handy for square footage, etc.

Out of the meter cans, each SE cable is #2 SEU. These enter through the rim joist into the basement of each duplex. There is a dividing wall between basements.

I am not trying to eliminate the jumper from one panel to the GEC. Just wondered if that jumper needed to be crimped onto the GEC, or if splitbolt is ok.

For what it's worth, the setup of 4/0 AL to meters, then #2 SEU to panels is pretty standard here. Both of the local utilities I deal with and all the AHJ's in the area accept this setup as standard for a duplex.


John

BTW, the jumper to the GEC is just run over the top of the dividing wall to the GEC from the other panel and splitbolt connected. No bored holes. The dividing wall is notched for plumbing, cable tv, and telephone lines and I just ran the jumper through that hole (about 3 feet long jumper I'd say).

 

[George Stolz]

John, I would say that perhaps you won't win this discussion with the inspector. Both sides can look at the installation and see their own point of view. Perhaps, in the end, it's worth just installiing 40' more #4 to the water main and forgetting about it.

It looks like a grounding electrode tap. It also looks like a grounding electrode conductor. It could go either way. If the inspector's boss (the AHJ) looks at it and decides to confirm the inspector's decision, then it is officially a GEC and then the split bolt is no good (90.4).

What state are you in? If your service conductors are allowed to run across the basement ceiling of the first unit to get to the second unit, that's one of the more liberal interpretations of the service rules I've heard.

 

[flick]

What state are you in? If your service conductors are allowed to run across the basement ceiling of the first unit to get to the second unit, that's one of the more liberal interpretations of the service rules I've heard.

No, the service conductors pop in through the rim joist and the panels are right below where the cable comes in. About 2.5 feet of SE cable from outside to the panelboard. The meter can is mounted at the center of the building.

 

[George Stolz]

Thanks for the lightbulb sensation over my head.

 

[Davis9]

What state are you in? If your service conductors are allowed to run across the basement ceiling of the first unit to get to the second unit, that's one of the more liberal interpretations of the service rules I've heard.[/QUOTE]

New here, but why would this be a liberal interpretation? If it ran across ceiling it would have to have a disconnect outside and no longer is considered a service conductor. It would be a feeder, IMO.

Tom

I think that the GEC would be the Water Pipe that is located in the basement of the building the service is attached to. As long as a fire separation wall is installed between units they would be considered two seperate buildings. Now the panel in the second building would have to be bonded to the water piping system in that building via the ground bus.

Maybe it's all moot if the Metering is installed dead center of the two buildings.

 

[George Stolz]

What state are you in? If your service conductors are allowed to run across the basement ceiling of the first unit to get to the second unit, that's one of the more liberal interpretations of the service rules I've heard.

New here, but why would this be a liberal interpretation? If it ran across ceiling it would have to have a disconnect outside and no longer is considered a service conductor. It would be a feeder, IMO.

Tom, welcome to the forum.

If there is no disconnect, they would be service conductors. If they were running the way I first pictured them (diagram at the top of the second page of this thread), and through the ceiling of the basement, then that would be wildly liberal. As it is, I was mistaken in my first idea.

I think that the GEC would be the Water Pipe that is located in the basement of the building the service is attached to.

By this, do you mean the Grounding Electrode Conductor (GEC) should be connected to the water pipe that physically enters Unit #2, as opposed to where it enters Unit #1's basement? As in, the first five feet are where it enters #2's basement?

As long as a fire separation wall is installed between units they would be considered two seperate buildings.

I think the notches in the rim joist seem to indicate a lack of firewall, but I'm not sure. However, I think your idea has merit. (Not just because it supports my 'two services' theory. )

Now the panel in the second building would have to be bonded to the water piping system in that building via the ground bus.

Do you mean the grounded conductor bus? 250.24(A).

Maybe it's all moot if the Metering is installed dead center of the two buildings.

Why's that?

 

[Davis9]

You are right on the first point if there is no disconnect.


2nd if the Service is attached to one side of the structure(one building not the other)then the Water pipe inside that building is where the GEC is connected. Within 5 feet, with exceptions.

Fire separation can be penetrated as long as a U.L. listed method is used.



I was thinking 250.104A(3)

Then half of the service would be on both sides so would be on bothe buildings thus both water pipes would be used(both), use 250.64(F).

Edited :to add that I don't know how to do all that cut and past stuff very well!

Tom

 

[George Stolz]

Here is the revised diagram of John's (flick's) installation.

Edit to add: I'm not quite clear on your references to 250.64(F) and 250.104(A)(3). I'm not sure what you're trying to say.

 

[Davis9]

Well, if that is what He has then He should have just gone to the Meter Socket w/GEC.

Was thinking that Water Pipe was in Both buildings.

Tom:smile:

 

[flick]

The wall in the basement is not fire rated. It is not even a structural support down the center of the structure because it runs parrallel to the joists. The basement ceilings are uncovered and the joists are bare.

I haven't seen a residential service where the GEC is run from the water main all the way to the meter base. Is that common in some areas?


John

 

[Davis9]

The GEC has to be connected "at or before the first means of disconnect", may make life easier for you.

Tom

 

[flick]

Around here, it is always done "at" the disconnect as far as I've seen.

 

[George Stolz]

I haven't seen a residential service where the GEC is run from the water main all the way to the meter base. Is that common in some areas?

John, it's common around here to install Metermains (meter/main disconnect combination boxes) for this application. Actually, we'll stick with the same basic setup for as large a dwelling structure as you would normally see. So, essentially, yes, in my area it is extremely common to run the GEC all the way out to the meter location, because that's where our service disconnects are too.

With a single point for disconnecting, much of the thinking just goes away.

Some jurisdictions I've heard check in here on the forum consider a ground-rod connection in the meterbase (when it's meterbase only) to be inaccessible, due to the POCO seal. Some places, the POCO requires a ground rod under the meterbase but the installer doesn't get credit for it in their uses.

Based on my experience and what flies around here, I can't believe you're allowed to put the service handles in seperate basements in your area. Some folks hear that we put all our handles outside, and can't believe it due to the risk of vandalism. It's a big country.

 

[infinity]

Am I following this thread correctly?

You have:
-Two dwelling units with a common basement separated by a non fire rated wall.
-Two service disconnects not grouped together inside of the basement
-Two sets of service entrance conductors originating in separate meters
-A GEC from the two water mains to one service with a tap to the other
-A split bolt for the jumper to the second service

So the question is can a split bolt be used for this? When the two services are grouped together than you fall under 250.64(D) which allows taps without using crimp style connectors. Since the two services are not grouped does this change anything?

 

[flick]

Am I following this thread correctly?

You have:
-Two dwelling units with a common basement separated by a non fire rated wall.
-Two service disconnects not grouped together inside of the basement
-Two sets of service entrance conductors originating in separate meters
-A GEC from the two water mains to one service with a tap to the other
-A split bolt for the jumper to the second service

So the question is can a split bolt be used for this? When the two services are grouped together than you fall under 250.64(D) which allows taps without using crimp style connectors. Since the two services are not grouped does this change anything?

Yes, that's the setup. I guess I never thought about the grouping of the disconnects, and apparently noone else around here has either. This setup is very common in this area. About the only time you'll see meter/mains here is when the panelboard is more than 5 - 7' from the point of entrance of the SE cable.


John

 

[George Stolz]

When the two services are grouped together than you fall under 250.64(D) which allows taps without using crimp style connectors. Since the two services are not grouped does this change anything?

My thought was, if the handles are grouped it's a single service, and therefore 250.64(D) is readily applied.

I can't see a path for calling this a single service, if the handles are not grouped. It could just be my own mental hurdle, but I can't get past it in my head.

On a side note, ditching the jumper altogether would also have the added benefit of not serving as an alternate neutral path between panels, too.