I will preface my question with the existing conditions of this install. We are working in a 13 story building which has been around for quite some time, and we have installed a new 1200 amp panel on the 13th floor of the building (it’s a mechanical room and the panel is meant to serve new HVAC equipment while powering some existing circuits). We installed 4 parallel feeds to supply it, and they come from the sub basement of the structure, which is 2 floors underground in the parking structure. This is where the switchgear/service equipment is located. We are about to install a transformer on the 13th floor fed from our 1200 amp panel, so my main question is how to bond to building steel if there’s none available (or at least none that isn’t buried under inches of concrete) and no other means is available. I’ve always bonded to building steel or a grounding electrode etc. just haven’t seen this particular situation before. I have a few code references I’ve found, but nothing solid. What are your thoughts?