I dunno exactly but there's a practice involving metal conduit between meter box and panel: If there are concentric rings left on either the meter box or panel enclosure after installing the conduit, a bonding wire must be run through the conduit from meter box to a grounding/locking bushing on the panel side I guess because the remaining concentric rings are easily damaged and are therefore not a reliable bonding connection. Marc That's basically it, but it only applies to the connection at the service panel. As far as I know, you don't have to worry about it after that. ...so the knockouts, isolated so much by their nearly all around cuts, don't have enough area in common with the box to make a bond. BTW what happened to the red wire feeding the sub? I only see black ones coming in there, with one taped white. There is no red conductor for the feed. There ar two blacks, one behind the other. The other arguments throughout the thread about eccentric or concentric knockouts is moot for voltages under 250.