maintenanceguy.the greenlee or ampprobe tracer.(not your voltage/amprobe) will locate the short in the conduit.
ground/floor/ceiling.but you have to follow the path of the signal.
with the wires connected on the circuit breakers did you try to turn on one at a time.?did it hold or trip???
did they pull one neutral for all 3 circuits or 3 neutrals
check the exhaust fans,you said there are 3 of them.go to the first 1900 box closest to the panel and disconnect the wiring for the fans and check again for a short at the panel.
