From searching the code, I can find only three places where bonding bushings are required. Around concentric and eccentric knock outs are two of them. The other is on the line side of the service, so I plan to put a bonding bushing on the new transformer but do I need one on the line side of the feed to the new panel?
Thanks for the tips and additional information. Now when I am reading it seems to indicate that bonding bushings are only required on the line side of theservice entrance conductors coming into service equipment, so since I am adding a transformer that is far downstream from them, I take it to mean that one is not required. That is also considering that the transformer is not establishing a new service because there isn't a meter being added.
Thats correct. I am assuming you have a transformer with voltages of 480/277 and 208/120, either on the primary or secondary. Whichever side the 480 is on will require bonding IF a concentric knock out is used.
Make sure you use a non-metallic raceway off your XO to the GEC, or you will have to bond it as well.
Section V of article 250 starts at 250.90, where it is made clear that in any situation where the electrician suspects that grounding continuity is not too good, he will have to bond. Bonding bushings MAY be used for this purpose. I teach my apprentices that we have levels of required bonding. The most restrictive level is " At the Service" (250.92), followed by "Over 250 Volts" (250.97), and then "Other Enclosures" (250.96).