Double Bonded

[jwatts]

Just finished installing a stand by whole house generator. The ATS was mounted adjacent to the meter outside. I bonded the ATS since this is now my service disconnect. Problem I found is that I can not find a bonding screw inside the existing 200 amp panel. It is a Murray panel. The bus bar on the left is all grounds, and the one on the right is all neutrals. Both bars are bonded to the enclosure. There is also a strap that ties the two bars together. Pretty sure I am double bonded? I believe this is a problem. Please confirm, and advise on how to resolve the issue.

 

[augie47]

From what you say, I believe if you look closely at the panel nameplate you will see "suitable as service equipment only". Pretty common for manufacturers to make these and fasten the neutral bars securely to the can.
On possible solution, if your AHJ will accept that you are altering the listed panel, would be to install an isolated neutral bar for your grounded conductors.

 

[texie]

Augi raises a good possibilty. The key here is the word "only" as in SUSE ONLY. If it says just SUSE and has no "only" with it then the bond screw or strap must be there. While I have seen much SUSE ONLY equipment, I don't recall any being Murray/Siemans load centers but it is sure possible. Sounds like a panel change out is in store for you if you can't change the neutral bar to be isolated.
On another note, I trust you have a SUSE transfer switch (or a separate new main disco) and have relocated your GES to that?

 

[Pierre C Belarge]

Is the location of this installation in Chicago or a suburb of Chicago?

 

[jwatts]

Installation is in the suburbs, so it doesnt fall undr CEC. Also, the transfer switch is service rated with a disconnecting means. GEC is relocated to the ATS. So if the AHJ is ok with it, I will have to isolate only the bus bar containing the neutrals. Also, could someone explain exactly why being bonded at two points is incorrect. I know it is wrong simply because I was taught it is wrong. However, never really had it explained to me why. Thanks!

 

[charlie b]

Also, could someone explain exactly why being bonded at two points is incorrect. I know it is wrong simply because I was taught it is wrong. However, never really had it explained to me why.

If you bond N to G in two enclosures, then the neutral wire and the ground wire that are run between the two enclosures will be in parallel with each other. You get parallel wires by connecting them at both ends, and that is what you will have here. But the neutral wire is intended to carry current and the ground wire is not (unless there is a fault, and then only briefly). Then, presuming the conduit between the enclosures is metal, that conduit will also be in parallel with the neutral and ground wires, so the conduit itself will be carrying current. As a result, it will be dangerous to touch the conduit. But even if the conduit is PVC, any and all normally-non-current-carrying-metal components that are bonded throughout the building will be energized. The voltage level will be small, to be sure. But it could be enough to make it unsafe to touch anything metal in the whole building.