new 400amp Comm. service bonding

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CopperTone

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MetroWest, MA
I have posted before this service scenario now I an at the proper bonding requirements. Here is the layout and type of system.

120/208V 400 Amp 3 phase 4 wire coming in from street underground in Rigid steel conduit.
Hits a 400amp non fused disconnect then the CT cabinet then the 400amp MCB Panel.
No building steel (wood framed) with a 1 1/2" water service coming in near it - metal pipe.

Now I know I want/need 2 ground rods with #6 tied into the main disconnect. I also will use 250.66 to bond the water piping which is a 1/0.
My grounding conductor will originate from the main non fused disconnect? And continue though all the equipment looping through bonding bushings and lugs on each cabinet and land on the ground bar in the MCB Panel?
My question is bonding bushings - Do I need to bond both ends or just one end of each section of conduit between each cabinet? I thought it was just one end.
I saw some of those bonding pictures posted here before
thanks
 
You need to make sure each conduit and cabinet is bonded.
If the cabinets are bonded by a bonding conductor (wirew) (or grounded conductor) then all you would need to do is assure each service raceway is bonded on either end. This could be by a hub, grounding locknut (if not concentric or eccentric knockouts) or bushing (or per other 250.92 means)

If you are depending on the conduit to be the grounding means from cabinet to cabinet (without a wire connection) then you would need to bond both ends.

I hope this makes sense.
 
so if I am not using an additional wire for the grounding conductor then I would bond both ends of the conduit through the entire run (grounding locknuts) then I would keep separate the neutral bar and ground bar in the 400amp MCB panel to avoid a parallel path for objectionable current.

I would need to bond every cabinet to the grounded conductor still.
 
I have to be careful and not mix apples and oranges here.
To me we have two seperate issues.
Bonding service equpment and bonding raceways.
Addressing the raceways. 250.92 states serice raceways must be bonded by an acceptable means listed in 250.92.
This, to me, would mean each section of raceway would have to be bonded on one end by an acceptable means. If a metallic nipple is installed between your disconnect and meter cabinet, that nipple would need to be bonded on at least one end.
So address each nipple seperately to see if it is bonded.
If you are using the nipple as your bond means (conductor), then both ends would need to be addressed. In this scenerio, if the disconenct is bonded by connection to the neutral (grounded) conductoir then it is bonded.
If the meter cabinet is bonded to the neutral, then that connecting nipple only need bonding on one end. If the meter is not bonded by the nerutral or a bonding conndor but is depending on the nipple to be the condictor, then that end of the nippple would need an acceptable (250.92) bonding means to attach the cabinet.
As far as neutral bonding....it might be more debatable. In this scenerio, I would consider everything to be ahead of your "service" MDP panel and I would bond the meter disconnect and meter can to the neutral and use (1) bonding means (locknut or bushing) on each nipple.
Everyoine may not approach the equipment bond that way.
 
. . . Hits a 400amp non fused disconnect then the CT cabinet then the 400amp MCB Panel. . .
I think everyone is missing that the 400 ampere non fused disconnect is a meter disconnect and it is not your service. Your grounding conductor is to be derived in the service, not the meter disconnect. :smile:
 
I think everyone is missing that the 400 ampere non fused disconnect is a meter disconnect and it is not your service. Your grounding conductor is to be derived in the service, not the meter disconnect. :smile:
I don't think our utilities around here would allow a disconnect before the meter. Someone could easily shut it off, and possibly steal electric from inside the ct cabinet. Some won't even allow connections inside unless they're irreversible.
 
I

My grounding conductor will originate from the main non fused disconnect? And continue though all the equipment looping through bonding bushings and lugs on each cabinet and land on the ground bar in the MCB Panel?
My question is bonding bushings - Do I need to bond both ends or just one end of each section of conduit between each cabinet? I thought it was just one end.
I saw some of those bonding pictures posted here before
thanks


This "grounding conductor" is not required. For bonding on the line side of the MCB you would only use the neutral to bond the metallic parts of the non-fused disconnect, the CT cabinet and the service raceways. Each section of raceway containing the service entrance conductors requires bonding beyond the use of standard locknuts. You may use a bonding bushing or another method outlined in 250.92 This requirement is only for one end of each service raceway.
 
The utility is requiring the main disconnect first upon entering the building. it is also inside a locked electric room.

I think everyone is missing that the 400 ampere non fused disconnect is a meter disconnect and it is not your service. Your grounding conductor is to be derived in the service, not the meter disconnect. :smile:

I agree with you here. My thoughs were to bond the 400 ampere non fused disconnect to the grounded conductor, use bonding type locknuts at least on one end of each "nipple or short section of conduit" between each cabinet, then bond the MBC panel to the grounded conductor and derive my grounding conductor from there, bonding my water pipe from there and landing my ground rods there too. (Not keeping separate the neutral and grounds)

I figured that is where the main service begins - not at the 400 ampere non fused disconnect which is used for servicing the meter - the wires come into the building underground from a manhole - the utility would have a hard time shutting off the power to the building.
So, would you all agree with this?
 
assuming your CT cabinet is bonded by the grounding conductor also, what you describe appears to be Code compliant.
(note: locally, POCO locks the meter disconnect to prevent tampering)
 
So do we. :smile:

Charlie, he mention NF disconnect. I agree with that from a
"logic" standpoint, but have concerns for AIC ratings on most jobs.
(mist NF I've seen are 10k)
How do you handle that ?
 
. . . How do you handle that?
We don't really make a big deal out of it since it is for our use only, it doesn't interrupt anything, and has no overcurrent protection (it is used as an isolating switch). In my opinion, the switch should be rated for the available fault current. That would be a fusible switch with shorting fuses (tubes) instead of standard fuses. :)
 
POCO here is lookimng into it. They didn't realize the NF were low AIC.
Now it's a jurisdictional thing.... POCO switch wired by contractor ...elect insp vs POCO
 
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