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#83015 - 01/01/03 03:32 PM Main Bonding Jumpers
Nick Offline

Registered: 08/13/01
Posts: 603
Loc: Riverside, CA
I have a question I have been pondering. I am installing a 2000A 480/277Y switchboard that has multiple metering capabilities. Section one is the utility pull section. To the right is section two a combination meter and 100A disconnect for “house power.” Section 3 is a meter/ 1000A disconnect for TI power. Section 4 is a distribution section for the TI Power. The un metered bus runs through sections 1,2 and 3 with bus tapping off to the service breakers at sections two and three. The ground bus runs continuous through all sections with the grounding electrode conductor connections in the 1000A main sections. The 1000A breaker has ground fault protection. There is future provisions for two 400A meter mains to the left (and around a corner) of the utility pull section. My question is this: Do I connect the main bonding jumpers in both the 100A main section and the 1000A section? Or do I just connect one because the ground bus is continuous to all sections.

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#83016 - 01/01/03 04:25 PM Re: Main Bonding Jumpers
electric-ed Offline

Registered: 07/08/02
Posts: 184
Loc: Canada
One main bonding jumper of the correct size is sufficient, connected between the grounded (neutral) bus and the grounding bus. This is normally done in the main disconnect section at the same point that the grounding electrode conductor is connected.


#83017 - 01/05/03 02:09 AM Re: Main Bonding Jumpers
Scott35 Offline

Broom Pusher and

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA

Just adding to Ed's reply; One GEC is needed to bond this gear + system to the building's GES.

Land it at the "usual" place - with regards to the "Neutral Disconnect" link.

How's everything going with your Anaheim project? Might be nice to drop by and visit you before my work load becomes "all encompassing" again!

Maybe Scott W (Electure) and I (Scott35) could meet you???
(a thought, but would you be able to handle two Scotts??? ...)

Scott s.e.t.
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#83018 - 01/05/03 08:28 AM Re: Main Bonding Jumpers
Nick Offline

Registered: 08/13/01
Posts: 603
Loc: Riverside, CA
Anaheim is all done and up & running. A lot of work but it sure was a nice boost in the pocketbook at Christmas! I would like to meet up with you guys but I am not sure when I will be back to OC. I am headed to the San Diego division next week to help on a bid for a job they want me to run. (It is with ***** and we have to interview for the project as well as bid it) They have been trying to get there hands on me since did Legoland. The right deal just hasn’t come up. ($$$$ ) I will e-mail you if I am going to OC any time soon and maybe we can meet up.
As far as the main bonding jumpers go, I connected one in each cabinet. They are the bus links that the switchgear manufacturers leave there for us. After looking at the bus layout it seemed to be ok weather one or two was hooked up. I was originally worried about problems with the GF system on the 1000A breaker. The neutral current transformer is placed in such a way it will work either way. There is no “main” disconnect in this line up. The six disconnect rule is being utilized. 250.28 states as a general rule that a main bonding jumper shall be connected within the enclosure of each service disconnect. In this case I have two service disconnects in two (attached) enclosures. Exception #1 goes on to talk about more than one service disconnect in an assembly listed for use as service equipment. (This is what I have.) “an unspliced main bonding jumper shall bond the grounded conductor(s) to the assembly enclosure.” “An” meaning one and only one? Or at least one? I just figure that if I connect say only the one in the 1000 am section, a fault in the 100A section would have to travel backwards to MBJ in the 1000A section before getting to the common grounded conductor bus. It would probably be fine but it doesn’t make since. The worst thing that could happen with the MBJ connected in both enclosures is I now have a parallel path within a listed assembly. Any problem with this?

[This message has been edited by Nick (edited 01-08-2003).]


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