In the USA the NEC requires, on panelboards, for the high leg to be on phase B. It must also be orange, or by other effective means. If running a 240V single phase load from this system, you could tap A-B, A-C or B-C, but with a catch. Most two pole breakers are rated 120/240V, in this case you cannot tap B because B is 208V to ground so you'd have to go A-C. There are straight 240V breakers available but these are special order and you can forget about walking into your local home depot and picking up a straight 240V two pole breaker. Typically this system is found in older commercial and industrial facilities, as well as some newer facilities in extremely specific applications. Only useful where most of your loads are 3 phase motors, with a small amount of 120V equipment. Load balancing tends to be poor when compared to a more common 120/208Y system. Also a very easy and costly mistake is to connect a single pole breaker to the B phase thinking your getting 120V, and smoke up everything on that circuit when the breaker is turned on.
In the USA the NEC requires, on panelboards, for the high leg to be on phase B. It must also be orange, or by other effective means. If running a 240V single phase load from this system, you could tap A-B, A-C or B-C, but with a catch. Most two pole breakers are rated 120/240V, in this case you cannot tap B because B is 208V to ground so you'd have to go A-C. There are straight 240V breakers available but these are special order and you can forget about walking into your local home depot and picking up a straight 240V two pole breaker. Typically this system is found in older commercial and industrial facilities, as well as some newer facilities in extremely specific applications. Only useful where most of your loads are 3 phase motors, with a small amount of 120V equipment. Load balancing tends to be poor when compared to a more common 120/208Y system. Also a very easy and costly mistake is to connect a single pole breaker to the B phase thinking your getting 120V, and smoke up everything on that circuit when the breaker is turned on.
Long be the high leg. Down with the wimpy Wye (120/208).
What if all legs read 120v on a 3phase 208v panel?