Thanks for the reply iwire. I’m sure my question seemed pretty dumb to a lot of folks here. I sat through a 4 hour seminar last night on transformers at the local tech school. Only the final 15-20 minutes covered connections. There is much confusion in our industry concerning grounding and bonding. My particular confusion comes in where parallel grounding paths might occur.
The particular transformer in question came with a factory installed bonding strap. If the XO terminal is bonded to the enclosure, and the secondary neutral and equipment ground are bonded at the XO terminal, then why the need for the additional chassis ground?
Another confusing issue at times is the requirement to bond the chassis to the building steel in certain situations. This particular building has a steel roof supported by steel joists, but no evidence that this steel is attached to anything other than the masonry building. The transformer is suspended from these joists by threaded rod and steel channel. If this building steel was not attached to earth and a high amperage fault occurred through the chassis, I wonder what would happen?
The transformer is installed per the code and is operating lighting & power as we speak. I went ahead and bonded it like the local inspector wanted it which is pretty much like your drawing.
Sorry to be so long winded, but I want to get to a point where I feel I have a competent understanding of grounding and bonding, and the reasoning behind the code requirements.
