We've been through this at least twice before. Yes, it's just for redundancy, something required by UL incase the line cord is pulled. Can't have all that premises wiring on one side of the system and the outside CO lines on the other without a ground.

My experience is that the supplemental ground should always be connected to the same point as the line cord ground. This ensures that there will never be a voltage differential between the two that will damage the equipment. You can never be certain that there will always be a zero potential between the receptacle ground that the system is plugged into and another point such as a cold water pipe or building steel.

Racks and enclosures should also be bonded to the same point that the equipment they contain is grounded to. I've seen in excess of 50 volts between the receptacle ground and building steel. In addition to a shock hazard it creates a dandy ground loop.

Secondary CO line protectors are another story if they are located with the equipment. You don't have to worry about a voltage differential there and you want a solid low impedance ground. So a cold water pipe, building steel or the electrical service ground is what you want and you want to use a substantial size wire.

-Hal

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