MBJ and GEC for Multiple Main Breaker Panels

[Jerramundi]

Hey all. Trying to help a friend out who just bought a building and really not used to the grounding and bonding of multiple main breaker panels.

Single main breaker panel I got. Single main breaker panel and sub panel(s) I got. Multiple main breaker panels are not really something I deal with regularly... so any clarification you guys can offer would be extremely helpful.

THE SET-UP: It's a two family building. 3-wire, single phase system, 200A 3/0 AWG wire in a single riser going to a (3) triple meter bank.
From the (3) triple meter bank, they have (3) separate raceways, each containing 3-Wire, single phase, 100A #3 AWG wire and feeding (3) separate 100A main breaker panels (public, 1st floor, and second floor).

If my understanding is correct, I need...

(1) A #8 AWG Main Bonding Jumper in EACH Main Breaker Panel sized according to 250.28(D)(1-2)... which needs to be continuous in bonding (1) the enclosure, (2) the EGC's, and (3) the ungrounded/neutral bus bar.

What I'm thinking about doing is starting an MBJ at the EGC bus bar, feeding it through a bonding bushing on the service entrance raceway to the neutral bus. Does this sound correct? I'm working with older, existing Challenger panels so there is no green screw to bond the neutral bus to the enclosure.

(2) A #6 GEC from the street side water main, bonding bushing on both ends of the raceway, to each individual neutral bus bar.

This is where I get somewhat confused because I'm not used to running a the GEC to multiple main break panels. Would I terminate this in the first panel and run a second wire run through a raceway to the 2nd and 3rd panels and their respective neutral buses? Or does it also have to be continuous? Would each intermittent raceway also require a bonding bushing on both ends?

Thanks in advance all! Stay safe.

 

[texie]

Are the 3 main breakers located next to the meter?

 

[electrofelon]

Your MBJ detail looks ok. I had to think about it a bit as I cant remember the last time I used an MBJ that wasnt a screw or strap. One question though, if these were existing panels, what was there for an MBJ before?

For the GEC, see 250.64(D), it gives you several options. I would likley use the "common location" to the meter socket, or the "GEC busbar" method.

 

[Jerramundi]

Are the 3 main breakers located next to the meter?

They are not. The meters are outside. The 3 Main Breaker Panels are in the basement.

 

[Jerramundi]

Your MBJ detail looks ok. I had to think about it a bit as I cant remember the last time I used an MBJ that wasnt a screw or strap. One question though, if these were existing panels, what was there for an MBJ before?

For the GEC, see 250.64(D), it gives you several options. I would likley use the "common location" to the meter socket, or the "GEC busbar" method.

NO MBJ before. Just one GEC to the water main off the public panel. Nothing on the other panels... and one ground rod outside off the meter bank. We actually had an issue of a circuit on the first floor unit grounding out and not tripping the breaker because of this.

I'm not sure what you mean by "common location" to the meter socket. There is already an existing GEC from the meter bank to a ground rod. I'm talking about the other GEC inside the building to the water main... and how to terminate this correctly in (3) separate main breaker panels.

 

[Little Bill]

They are not. The meters are outside. The 3 Main Breaker Panels are in the basement.

So no breakers outside at the meters?

 

[Jerramundi]

So no breakers outside at the meters?

No sir. Short 5 ft run from the meter bank to the panels inside. I'm not sure what the distance requirement is before you have to hit a disconnect on the feeders inside a building, but I'm fairly certain we are covered.

Any thoughts about how to terminate the water main GEC on 3 separate main breaker panels? Or if my MBJ installation sounds correct?

 

[texie]

I would just use the ground bus method as electrofelon suggested. It's easy and flexible. It's a commercially available item that is 1/4" X 2" X what ever length (6"'12", etc. Comes as kit with mounts. Just run all of your GECs to that.
Then just make the appropriately sized MBJ for each main. Are you metallic service raceways bonded per 250.92?

 

[electrofelon]

No sir. Short 5 ft run from the meter bank to the panels inside. I'm not sure what the distance requirement is before you have to hit a disconnect on the feeders inside a building, but I'm fairly certain we are covered.

Any thoughts about how to terminate the water main GEC on 3 separate main breaker panels? Or if my MBJ installation sounds correct?

did you read 250.64(D)? Probably best if you familiarize yourself with that, then come back with any questions

 

[texie]

They are not. The meters are outside. The 3 Main Breaker Panels are in the basement.

Are they grouped?

 

[Cow]

For the GEC, see 250.64(D), it gives you several options. I would likley use the "common location" to the meter socket, or the "GEC busbar" method.

I like the GEC busbar method, although was recently shot down on a MV pumpstation install using this method by a Washington inspector. In the interest of getting water on for crops, we relented and changed it to a full sized GEC(wire) with irreversible Burndy crimps for the taps to the individual service disconnects.

Be sure your inspector is on board with this install. It's code compliant, but it never hurts to discuss with your inspector beforehand because some inspectors may not see this method used much(or ever before, as was our case).

 

[texie]

I like the GEC busbar method, although was recently shot down on a MV pumpstation install using this method by a Washington inspector. In the interest of getting water on for crops, we relented and changed it to a full sized GEC(wire) with irreversible Burndy crimps for the taps to the individual service disconnects.

Be sure your inspector is on board with this install. It's code compliant, but it never hurts to discuss with your inspector beforehand because some inspectors may not see this method used much(or ever before, as was our case).

The inspector needs some training. You must be more easy going than me. In my old age I just won't tolerate inspectors like that.