I'm backing out of this. We are now at a point where you have an ungrounded 3ph3w delta and now are expecting that that the "4th wire" when run with the other 3wires will actually provide a ground for the newly derived 3ph3w ungrounded delta system.
No. Not what I said.
The OP needs to find out what industrial installation technique they used. Since the building primary is Delta the building must have a grounding electrode system present.
My guess from here is that they ran a four bar buss and therefore labeled panels as "4-wire", which they aren't. A four bar buss at such a site will be a 480 3-wire system with a GES tied to the fourth bar - not a neutral.
Alternately they ran a three bar buss. Then when they make a machine drop they bring a 4th wire from the GES tied building steel. In which case someone probably saw four wires in the drop and again presumed it must be "4-wire", which it's not.
A lot of machine tools use the ground for protection and leave the three-phase floating. They don't use a neutral in any fashion.
On the other hand, if you
need the neutral such as for 277 lighting then you have to install a Delta-Wye transformer for the lighting. That allows you to create a neutral on the secondary side.
In an industrial installation someone not paying attention
could wrongfully treat the GES like a neutral. There's typically enough magnetic linkage that the 3-wire system centers its voltage so it
appears to be 277 to ground. It'll function
most of the time since the linkage is typically very strong. It usually shows up as short bulb life due to the voltage instability.
Same with a machine tool. If someone presumed that it was 4-wire just because the drop has four wires coming down, then the machine components will have a shorter life span and frequent controller faults. Just because the magnetic linkage makes the 3-wire read 277 to ground doesn't make the GES a neutral. But if you measure thinking it's a 4-wire and see that reading you may fail to understand why it's down all the time.
I've been at my industrial site for 30 years. I
know it's 3-wire with GES building steel. In all that time I've never seen or heard of anyone reading less than 250V or more than 284V to ground on a functioning buss.