North America uses three-wire AC distribution system. Two LINE wires feed 120VAC, 180° out of phase. The third wire is a return or NEUTRAL wire. For 120VAC you connect to one LINE and NEUTRAL. For 240VAC you connect to both LINE wires.

 

How do you get the other 120VAC phase? I must have read something but I don't remember now.

For domestic AC power distribution, a single-phase high voltage feeder runs around on poles. This drives the primary of a step-down power transformer. The secondary is center-tapped, so you can use it as both a single 240 V line, and two 120 V lines that are 180 degrees out of phase. The center-tap connection is called the Neutral.

ak

 

For domestic AC power distribution, a single-phase high voltage feeder runs around on poles. This drives the primary of a step-down power transformer. The secondary is center-tapped, so you can use it as both a single 240 V line, and two 120 V lines that are 180 degrees out of phase. The center-tap connection is called the Neutral.

ak

Every single house/building has this transformer?

 

No. A feeder can drive multiple transformers, and a transformer can supply multiple houses. The one on a pole in my neighbor's yard supplies three houses from one secondary.

ak

 

Every single house/building has this transformer?

Not sure about everywhere. But my next door neighbor and I share one. Many people call them "pole pigs".
https://en.wikipedia.org/wiki/Distribution_transformer

 

Not sure about everywhere. But my next door neighbor and I share one. Many people call them "pole pigs".
https://en.wikipedia.org/wiki/Distribution_transformer

I don't remember but I think residential lines are a 600v feed that gets stepped down by a transformer on the pole, to 220v at the service entrance on most residences. The actual electric panel amperage can vary from 60 amp to 200 amp, the later being an updated service requiring proper line size from the connection to the pole to service entrance, meter pan upgrade and circuit breaker panel upgrade.

 

Not quite sure I follow you.
Your house is supplied with 120VAC or 240VAC.
The usual way to bring this down to 12V is to use a step down transformer. Most houses with door bells and HVAC installations use a "bell transformer" to bring the voltage down to 24VAC or 12VAC.

The reason to have what is the "controls" power transformer fed by 240 volts is at least partly so that ifone side of the 240 volt feed is missing the system should not work. So an unsafe condition is prevented. The other reason is that if nothing in the system requires 120 volts, then no neutral connection is required, at least in some areas. That cuts out the cost of one heavy conductor in the power feed wiring. It also cuts out the cost of providing a neutral connection in the hot tub system.
"Why pay for what you don't need."

 

The yard/outside hot tubs I have wired used 120v 0(N) 120v plus GND.
240v for the Htr's and 120v for the auxiliary options etc.