On Mon, 18 Nov 2013 06:39:55 -0800 (PST), TimR
wrote:

I hate to display ignorance, and I know I should know this.

But maybe somebody can explain.

The power lines are 3 phase, meaning they're 120 degrees out of phase to each other

Yes.

allowing 3 wires to carry what 6 wires should (since they're generated by 3 sets of coils at the power plant).

Kinda sorta.

The house is fed by just one of these wires, through a center tap transformer.

Yes.

That transformer sends 3 wires to the house: Neutral, +120 volts, -120 volts.

Well... There are two AC wires that are opposite, yes. If you said
they were +120wt and -120wt, you would have a point (w being the
angular frequency, or 2*Pi*f and t=time).

Connect the two hots and you get 240, connect either hot to the neutral and you get 120.

Yes.

Your safety ground is bonded to the neutral and so you should also have 120 from any hot
wire to the ground.

Assuming no faults and ideal wires, sure.

Neutral is the center tap.

Yes. ...which is grounded.

Here's what I'm not getting at the moment. What are the connections to that transformer? If it is 3 phase leg to neutral on the primary side,

Yes. Almost always, though it really doesn't matter.

then the center tap should be above neutral on the secondary (house) side, right?

No. The center tap is grounded at both the transformer and the
entrance panel. It *is* ground.

Which would mean that house neutral is NOT at ground level. But I'm pretty sure it is.

It is. I don't see your problem. You described things pretty well.