This is not correct for the majority of US households. Two of the phases DO NOT run to the house, a typical US household service is split-phase. The primary w

This is not correct for the majority of US households. Two of the phases DO NOT run to the house, a typical US household service is split-phase. The primary winding in the transformer at the pole connects between a single phase and ground, and the secondary winding is center-tapped to provide a 'neutral', with 120v on either side of the neutral. The voltages are indeed 180 degrees out of phase. Your test would show 220-240v in the vast majority of US-based residential situations. The 120/208 you are referring to is when all 3 phases are fed in to a WYE transformer that has 3 120v secodary windings fed from a center point, which becomes the neutral. With a WYE transformer, each phase gets 120v to ground/neutral, and the phase-to-phase voltage indeed peaks at 208v due to the 120 degree rotation between phases. This is typically only found in large residential(600+ amps), and medium to large commercial and industrial buildings with 3-phase service. Another method would be using a 'Delta' transformer, in which one of the phase-to-phase windings are center-tapped, similar but a little different than the single-phase residential service. The two phases on either side of that center-tap will be 120v to neutral, but the 3rd phase will be 208v to netural/ground. This is usually called the 'wild' leg and is often used to power lighting loads. Source: I've been doing this for a long time. Also https://www.doityourself.com/forum/electrical-ac-dc/549775-laymans-explanation-240v.html https://www.doityourself.com/forum/electrical-ac-dc/549775-l... And https://ctlsys.com/support/electrical_service_types_and_voltages/ https://ctlsys.com/support/electrical_service_types_and_volt...