Time to put your inspector hat on. Had a intersting debate with myself on a code issue. I had a Meter/main that is back to back with the panel that is connected by a rigid nipple. In my right ups, I reference the code I refer so anyone who reads it can be on the same sheet of music with me. I came to a good conclusion but I wanted to bounce this off of you to stir up some good discussion.
The nipple beween the panel and meter main is rigid and for the the discussion, lock nuted on both sides of the panel and meter main. Would this be adequate bonding? 250.92 requires all service equipment to be bonded and the double locknuted is not an approved bonding method. However, the nipple, is not a service raceway but a feeder raceway. Would 250.92 still apply to the nipple? explain your position
Sparky, In my opinion, if you install the main bonding jumper and the connection to the GEC in the outside cabinet, then most inspectors would consider the outside cabinet only to be the service. In that case, double locknuts and plastic bushings would be fine for bonding the rigid nipple, because it is a feeder. Both the GEC and the main bonding jumper must connect to the same physical buss. The inside panel would have to have a separate neutral and ground bar because it is not the service.
However, if you install the main bonding jumper and the Grounding Electrode Conductor in the inside panel, then both cabinets constitute the service, which is also quite commonly done. No separate ground bar is required, though many people do install them. At least one bonding type lock nut or bonding bushing would then be required.
Another solution which many people use is a PVC nipple with panel adaptors and a coupling or male adaptors, locknut and plastic bushings. The grounded conductor (neutral) is still considered adequate for bonding the service cabinets if it exceeds the minimum size required for bonding.
Sparky, I was able to install a CT cabinet back to back with a very shallow 1200 amp service cabinet by using pvc nipples and panel adaptors. The 500MCM was a tight fit. If I had used rigid nipples, the bonding locknuts and bushings would have taken up too much room to fit the 500's in the panel.
your service ends at the exterior breaker. From the exterior breaker into the interior panel you have a feeder. You should also do all your bonding of the grounded and grounding conductors at the exterior location as that is the service. The interior anel should be wired as a subpanel
That's why they make bonding locknuts .... though I much prefer actually running a wire between the lugs and busses!
I once had a Thanksgiving interrupted when a 19 yr-old building had just such a locknut connection come loose - resulting in some interesting power surges and toasted surge suppressors. Once the neutral was a wire, and no longer depended on the raceway for connection to the PoCo neutral, all manner of power quality issues went away.