The 110VAC/220VAC thread, plus recent events at my home prompted this 
posting. See the paragraph enclosed in '*****' lines for the meat of the 
post.

I live in a suburb of Buffalo, New York. Some of you may have some news 
about a small storm we encountered here last week :-)

My power was out for over a week due to a tree falling on and breaking a 
primary line in my backyard.

In this case the wiring is done as follows:

Along a nearby major street, which runs perpendicular to my street, they run 
a three phase high voltage line. I am pretty sure that this is a 13,500 volt 
phase-to-phase connection (although they do not carry the neutral along the 
poles, I believe the service is referenced to earth ground via a WYE wound 
transformer or some other means at its source).

One of the three wires is then connected (via a disconnect switch) to a 
single conductor high voltage primary line running on insulators sticking 
out of  the tops of the poles which run down the center of my block (along 
the back fences). If the phase-to-phase voltage is indeed 13,500 volts, then 
this wire is at about 7800 volts from ground.

*******
Periodically, along this high voltage wire, a single phase transformer is 
mounted on a pole. The primary is connected between the single high voltage 
wire on the top of the pole, and a wire run down the side of pole and 
connected to a ground rod. In other words, the transformer's primary power 
is actually driven through the physical earth. This scheme is very scary 
because if ever the ground connection goes bad you will have the full high 
voltage (7800 V) present at the bottom of the pole! The wire used to provide 
this ground appears to be about 8 gauge, insulated wire. Its only protection 
from damage, besides its insulation, is a wooden molding with a U-shaped 
cross section which is stapled over the wire to the pole. The thickness of 
the wood in the molding is about 3/16" (5 mm). On many poles this molding is 
missing or damaged.
*******

By my count, there are 12 houses powered by the transformer nearest my 
house. They typically have 150 amp main service breakers. Assuming a typical 
load (say with air conditioners running) of about 40 amps per house at 220V, 
this comes to 480 A in the secondary of the transformer. Dividing this by 
the transformer ratio of 7800/220 we get a primary current in the 
transformer of  abound 13.5 A. This current is being sunk into the ground by 
the ground rod mentioned in the prior paragraph.

[When the weather clears up a bit, I intend to perform a little experiment 
by driving a couple of stakes into the ground, one right next to the pole 
with the transformer and the other a few feet away and seeing what 60Hz 
voltage I can measure between them.]

The secondary of the transformer is 220V center tapped and connects to three 
wires running from pole-to-pole about 2/3 of the way up the poles. Drops to 
individual houses then connect to those three wires.

At each house three wires connect to the 220V lines on the pole in the 
backyard (either via an overhead or underground line) to provide 220V from 
phase to phase and 110V from phase to neutral. The neutral conductor for 
overhead services is nearly always uninsulated in a 'triplex' cable (two 
insulated phase conductors and the uninsulated neutral twisted together in a 
spiral).

At each house, a safety (earth) ground is established by connecting an (8 
foot?) ground rod, the incoming water line and the incoming gas line all 
directly or indirectly to the service panel. In the service panel, the 
incoming neutral and this safety ground are bonded together. This prevents 
the neutral from "floating" relative to earth ground.

Bob Ammerman
RAm Systems 

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