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In the Forum: Audio Discussions
In the Thread: It’s mad, mad, mad... electricity.

Post Subject: MDB groundingPosted by JOHNR on: 11/24/2015

Paul,
Please be careful here because good ol' USA is quite different when using residential pole mounted feeder transformers.
What you may have is a neutral wire coming off of the 0 volts tap of the 120-0-120 secondary. This center tap is connected in turn to a ground rod using a substantial conductor. This is designed to handle a transformer failure in the event of the primary coming in contact with the secondary. This happens due to surges or lunatics stealing the above mentioned ground rod. The source voltage ranges from 9 to 15 kilovolts on those installations that I have come across.

The DB ground is most likely to be a ground rod located near the main cable entrance.
I would prefer to use this ground path simply because no matter what happens to the commercial supply, surge energy cannot get to this path.

In the case of Europe, this DB ground comes from a tap taken from the incoming cable armored sheath. This is designed to handle fault currents only.
It used to be grounded only at the feeder transformer but this has been relaxed but you are not allowed to fit your own ground. Besides, it is incredibly noisy.

The fundamental reason for the different methods used is the sheer length of such feeder systems. The power companies can support large areas using a single high voltage wire. The trade off is that there is no local voltage regulation and why hifi is such a problem when it needs clean power. Moving to SMPS based systems does away with all that as an issue.
Regards
John

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