High voltage wiring in residential area?

[Jamie Buxton]

Can somebody 'splain to me about the high-voltage wiring in my residential neighborhood? I've been looking at the tops of the power poles, and it makes me curious.

I'm talking about the high-voltage stuff -- the stuff that feeds all the transformers which produce the voltage fed to the houses. It seems to me that we'd only need two conductors with the high voltage on it. After all, all the transformers are only fed two conductors. However, at the tops of the power poles, I can see two conductors in places, three conductors in other places, and four conductors in other places. What is going on here? Why are there extra conductors? Spares?

[Scott T Smith]

Two conductors usually indicate the availability of single phase power, and 3 or more indicate the availability of 3-phase power.

[David G Baker]

What Scott S. wrote.

[Jamie Buxton]

Yeah, that might have been my guess. But this is a standard residential neighborhood, and there's no 3-phase. Furthermore, all the transformers on the poles are fed with just two wires, so it isn't 3-phase. And on top of that, as I said, there's 2, 3, and 4 wires on tops of the poles. Hence my confusion.

[Mike Henderson]

In some residential neighborthoods, where the power is fed above ground, the power company sometimes runs "low voltage" from a transformer along the top of the poles in order to feed additional homes from the same transformer. That's three wires - the two outside wires on the transformer and the center tap. In some places, the HV is terminated at a transformer and three wires continue but they're low voltage.

When I go walking in a neighborhood with above ground power, I often try to figure out the wiring and that's what I've observed in some places. It gets fairly complex sometimes trying to figure out what the power company did.

But for all the residential neighborhoods I've walked through, there's only single phase power available.

We have in ground utilities in my neighborhood and I had the opportunity to look down into one of the transformer pits. The high voltage power is brought in on a coaxial cable, where the center is hot and the shield is ground. I think that's somewhere around 44K volts but I'm not really sure. Pretty big cable.

That cable feeds into what looks like a standard distribution transformer (same as you'd see on a pole) and there are three wires coming out - two hots at 240V across them, and the center tap. Those go underground to the homes.

Mike

[Dan Friedrichs]

If the pole has a bare wire running along its side, that often runs from a ground rod up to the top conductor, which is a sacrificial lightning "rod" of sorts. This is more common on taller poles and towers, though.

[Jamie Buxton]

...In some residential neighborthoods, where the power is fed above ground, the power company sometimes runs "low voltage" from a transformer along the top of the poles in order to feed additional homes from the same transformer...

What happens in my neighborhood is that the high voltage lines are at the top of the poles. House-voltage lines run about six feet down from there, and the transformers are between the two levels.

[Steve Rozmiarek]

Mike, don't they feed a local substation with three phase, and drop voltage and split to single phase there?