Back when I used to install PBX's, the manufacturer REQUIRED a #6 (min.) ground wire be run from the PBX service panel in the PBX room to, with no taps, the xformer that provided the power. If we simply wired the ground to the panel that provided power to the PBX room or building ground then we would void the warranty. Also, nothing that was fed from the PBX panel could be in contact with building ground. With some of the installs being in the range of millions of dollars, we were told that we could loose our job if we didn't get the electrician to wire the ground "correctly." There were many times that this would lead to a heated argument between us and the contracted electrician. We did mostly new construction. To put things into perspective, some of the larger installs would require as much as up to 6-30 amp 220 volt feeds (if I remember correctly) and would power, truck sized banks of batteries and refrigerator sized inverters and rectifier units. The PBX's ran on 48 to 54 volts DC and each of the up to 6 rectifier units could pump out up to 50 amps DC. Was it simply a matter of the manufacturer not wanting to put trust in the local wiring? Was it a matter of trying to eliminate any chances of ground loops? Was it a matter of the manufacturer trying to get the cleanest power available? Was it just a Nortel nuance? ???
Just wondering.
Chris