MOTM

I would've guessed electrolysis too -- if only do to Paul's hint. I had no 
idea about the corrosion problems averted by using a positive ground, but 
I've seen water mains corrode in a few years when the originals lasted about 
twenty -- until the plumbers change them out and remove the ground straps 
(job insurance I guess).

I'll also note that the house I currently live in (probably built in the 
thirties or forties) doesn't have ground = neutral. I found this out while 
recently swapping out some stereo components -- holding a tape deck in my 
sweaty hands when my sweaty arm rubs against another component (OUCH!). 
Apparently each side is about 60 V about the ground pin.

Sweat is a good conductor!
JB

In a message dated 9/13/2000 10:31:09 AM, tony@... writes:

>It has to do with electrolysis. In a huge system like this, there will
>be
>leakage current into the earth. The leakage is through wet phone wires.
>In
>the process of electrolysis, corrosive action is confined to the anode
>or
>positive side.  When the wires are at negative potential compared to the
>ground the metal ions go from the ground to the wire instead of the
>situation where positive voltage would cause metal from the wire to leave
>which causes quick corrosion.
>