not in NEC and my electrician friend could not answer. Block wall, meter and service panel back to back connected with steel threaded pipe. The steel threaded pipe is the only means of bond between the two. Meter box grounded to electrode outside.
Is the steel pipe an acceptable bond for ground?
Walter
You need a bonding lock nut if the nipple is in the largest knockout. Or a bonding busing and jumper if it is in a concentric knockout.
A PVC nipple is MUCH easier in this case. NO bonding is necessary.
A PVC nipple also eliminates the “parallel neutral” problem caused when you have a bonding jumper in the service disconnect enclosure and the PoCo bonds the neutral in the meter base. They changed the code (2002?) to make this legal but it is still troubling to people who take 250.6 seriously.
All metalic raceways carrying service conductors need bonding connectors like Speedy says.