OT Metroliner telephone article 4104

Answers below refer to US-CA style power; the details will be different in 240V countries

I know you can transmit across the two halves of a single 240V circuit, so my presumption is that as long as all your devices are on the same side of the transformer they can talk, just not from one side to the other. I don't know enough about multi-phase transformers to be sure, though.

This also means that if there's multiple houses on the same transformer (very typical), you can talk to you're neighbor's network too. Not so good.

... unless you live in a low-density area served by a stub line, in which case there'll only be one phase up there. Many residential-only areas are designed so that there's one three-phase line running through the middle with single-phase lines going off to serve each street. They tap a different phase for each street to keep the load even.

Well, you get approximately zero Volts. The tolerances in a delta feed are still loose enough to kill you even though the sum is supposedly ground. That's why Y feed was developed, which is a delta feed plus a real ground. However, there's a lot of delta stuff still out there, and some new delta being installed because it's cheaper to run three wires instead of four. The really high voltage long-distance stuff is always delta for that reason.

Not even close. Distribution lines are measured in kilovolts; the exact number depends on the power company's whim when they installed it. The feed to individual houses is typically tapped off a single phase and transformed down to 240V, with a center tap so that you get two 120V circuits that are 180 degrees out of phase. This makes it convenient to mix 120V and 240V equipment in the same house.

S

-- Stephen Sprunk "God does not play dice." --Albert Einstein CCIE #3723 "God is an inveterate gambler, and He throws the K5SSS dice at every possible opportunity." --Stephen Hawking

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