2/3 way switching to follow

[SUNRAY]

American electricity supplies use a lot of tin can transformers. Often a tin can for every 2 or 3 houses

Not that it matters in the slightest but ironically that is a bad example of your statement as it's for a 3ph supply.

 

[bernardgreen]

that is a bad example of your statement

I agree, I have lost the photos I took of poles in a suburb of Nashville.

There was a 11kV circuit supplying the tin cans, then above that was another higher voltage ( 100 kV ? ) circuit with larger transformers feeding the 11kV circuits along the main road. Phone lines were strung underneath the electricity supplies with junction boxes in the middle of spans.

 

[SUNRAY]

I agree, I have lost the photos I took of poles in a suburb of Nashville.

There was a 11kV circuit supplying the tin cans, then above that was another higher voltage ( 100 kV ? ) circuit with larger transformers feeding the 11kV circuits along the main road. Phone lines were strung underneath the electricity supplies with junction boxes in the middle of spans.

My comment is based on the configuration of the transformers, I can't identify all of the primary wiring but I think it's wired Δ as shown in old colours and the secondary wired Y with earthed mid point as shown in harmonised colours:

Of course it's possible, but doubtful, this is is 11KV to 5KV or something.

 

[bernardgreen]

This chap is a bit confused about the reason for having a Neutral

and he also gives

as the Voltage of the supplies to the tin cans hung on poles.

 

[FrodoOne]

I strongly suspect that what is described in the second above illustration as "SECONDARY ELECTRICS 115/230 Volts" is NOT both of those voltages.

While the "usual" practice in North America is to supply each "premise" with a single phase 240 V secondary supply, "split" by using an Earthed/Neutral Centre Tap from a single transformer - so that there are two supplies of 120 V out-of-phase by 180 degrees - (as illustrated in the first picture), in some cases what is supplied is 2 out of 3 phases of 120 V secondary supplies (relative to the Earth/Neutral) - so that the supply derived from between two of these phases (out-of-phase by 120 degrees) is (only) 208 V.

The situation is shown in
https://www.thermalcorporation.com/208-volts-is-a-weird-voltage-where-did-it-come-from/
and "explained" in

and

This chap is a bit confused about the reason for having a Neutral

At 3:30 he is referring to the problem which occurs with a 240 V/120 V "Split Phase" system if the Neutral goes open-circuit. The two 120 V supplies are then in series and a high current device on one "120 V" supply will have a low voltage across it but a low current device on the other "120 V" supply (in series across 240 V) will have a high voltage across it.

(At 1: 50, isn't there a "phase conductor" broken off an "waving in the breeze"?)