The intent would to bond to building steel for lightning protection (It is a large steel manufacturing/warehouse building), not for use in the electrical ground system. The circuit grounds will still be provided. You have a good point though. We could form a ground mat and bond to the interior columns, then exit at one point near the electrical service ground and connect to the ground ring outside the building.
Is this lightning protection system being designed by a engineer or is this something the owner has spec'd
Are you a UL certified lightning protection contractor? I would be careful in how you word this kind of work in your contract as if you are not a UL certified lightning contractor, I would make sure the owners know this as they could come back on you if major damage to electronics was done in the event of a lightning strike if they are expecting protection, I would make sure you put in your contract that the work was spec by the owners or the engineer of charge and that any damage caused by lighting would not be covered.
It would have been nice if you had re-bar expose in these precast walls to bond to as they would offer you more protection by making it into a faraday cage around the building if you could bond each section to the building steel, I would not want to direct the lightning current into the building as even if it does dissipate into the earth it can still produce a EMP pulse into the circuits inside of the building that can damage electronics, you want to draw the energy outside and away from the building, most rings I have installed were 5' to 10' away from the building and at least 24" deep, putting rods at least 20' apart along the ring and using flat braided fine stranded copper cable to bond the ring back to the building metal or its electrical system GES, lightning is a high frequency event and the impedance can be very high using regular cable as the flat cable offers more surface area, keep in mind that the grounding in the NEC is not for lightning protection as many times or GEC's are too long to offer any protection from lightning because the impedance can be so high that lightning can't see or follow these paths.
Also many of these buildings will have multiple electrical paths into or out of the buildings at locations too far apart, to have a good lighting protection system require routing all conductors leaving or entering the building through what is called a ground window which acts like a choke to high frequency's as well as acting as a single conductor to lightning, which current can't flow if you only have one conductor, when we have several conductors entering a building at different locations we give the lightning a loop that its current can flow in, so there is allot to lightning protection and even the best design systems can still have some damage done in a lightning event the best we can do is keep it to a minimum by correctly designing the system and also using protection at the equipment that needs the protection such as good surge protection at both the service entrance and at the point of use.
So if you are not a lightning specialist or UL certified lightning protection system contractor then be very careful in how you offer this service as it can come back and bite you when things go wrong, make sure it is understood that you are offering to install this as spec'd by the owners or engineers and by no means are you guaranteeing it to provide the protection that a qualified lightning specialist would provide.
