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[Tom Bourke]

Actually, many (all?) high leg or wild leg services are really variations of a split phase service-they just add an additional transformer and create a 3rd phase.  So, the right way to deal with it it to use the 2 "normal" legs and the neutral just like you would use a single/split phase service. Leave the wild leg alone for anything other than 3 phase motors just to be safe.  IMO, this is a really good argument against the "2 phase" terminology.  Someone might think since single phase uses 1 transformer, and 3 phase uses 3 that if they see 2 transformers you have "2 phase" and that could lead to an interesting result.

No, high leg delta or wild leg delta, is not just a transformer off a split phase service for a 3rd leg.  It is 3 transformers off of a 3 phase service, one of witch has a center tapped secondary for 120 volt loads. Leg to leg is 240V.  Neutral to the wild leg is 208 and can typically handle 10% or less of the total system capacity.

All modern systems are 3 phase if you go far enough up stream.  There is the possibility of a utility company using 2 transformers to service an area from a 3 phase system.  It is a cost savings measure. The trade off is the cost savings of a transformer vs system capacity of the installed transmission lines.  If the area grows to the point of needing more capacity they can simply add the last transformer.

[John Sulek]

Just going to throw in here that there is the American way, and the European way.  For everywhere except Norway

+1
And parts of Spain.

[Stephen Swaffer]

No, high leg delta or wild leg delta, is not just a transformer off a split phase service for a 3rd leg.  It is 3 transformers off of a 3 phase service, one of witch has a center tapped secondary for 120 volt loads. Leg to leg is 240V.  Neutral to the wild leg is 208 and can typically handle 10% or less of the total system capacity.

All modern systems are 3 phase if you go far enough up stream.  There is the possibility of a utility company using 2 transformers to service an area from a 3 phase system.  It is a cost savings measure. The trade off is the cost savings of a transformer vs system capacity of the installed transmission lines.  If the area grows to the point of needing more capacity they can simply add the last transformer.

Tom, I have personally seen wild leg delta implemented with 2 transformers-my understanding is that that is a cost savings measure on the part of the POCO.  I have no doubt they use 2 transformers on a 3 phase system at times as well-but my experience is based on actual physical observation of both the install and working with it inside the building.

In either case, ignoring the high leg and using the 120/240 phases with their neutral should still give the same result as a normal single/split phase service since the neutral is not common to the high leg.  I would not expect triplen harmonics to create the same issue on this type of system.

[Tom Bourke]

Tom, I have personally seen wild leg delta implemented with 2 transformers-my understanding is that that is a cost savings measure on the part of the POCO.  I have no doubt they use 2 transformers on a 3 phase system at times as well-but my experience is based on actual physical observation of both the install and working with it inside the building.

For true 3 phase you need 120 Deg between the legs.  You can't create that with just a transformer.  In the case where you saw wild leg delta with just 2 transformers it was most likely a main transformer for the split-phase loads and a second smaller one for the 3rd leg in a V formation.  It would still have been 3 phase from the POCO.

I had to look up the proper term, it is Open Delta.  For more info:
http://forums.mikeholt.com/showthread.php?t=144067

[Frank DeWitt]

Well,  I'm glad we got that settled.

I think Mike is just going through a phase.

[Mike Sokol]

Well,  I'm glad we got that settled.

I think Mike is just going through a phase.

Yup...

[Stephen Swaffer]

For true 3 phase you need 120 Deg between the legs.  You can't create that with just a transformer.  In the case where you saw wild leg delta with just 2 transformers it was most likely a main transformer for the split-phase loads and a second smaller one for the 3rd leg in a V formation.  It would still have been 3 phase from the POCO.

I had to look up the proper term, it is Open Delta.  For more info:
http://forums.mikeholt.com/showthread.php?t=144067

You are right-it is run off a different phase.  Still my point being that the single phase/split phase transformer is the same as a single phase-so it can be used in the same way.  I made the assumption that open delta was the most common form because the primary reason for using a high leg scenario is to save the cost of a transformer. On the service distribution side it is nothing but a headache.

[Frank Koenig]

I'm a little late to the party but can't pass up the opportunity to argue about nomenclature. With all respect, I object to both "split-phase" and "two-phase" as names for the funky center-tapped system we use in North America. The problem is that both terms already refer to something else and, aside from just dulling the language, borrowing a term -- incorrectly in someone else's view -- can make one sound ignorant. Like calling the rear hatch on a hatch back passenger car a "lift gate", which all sound guys know refers to that toe crushing appliance on the back of a truck. I'm sure there are better examples.

Split-phase is a type of single-phase induction motor that uses a starting winding (without the benefit of a phase-shifting capacitor) to provide the necessary field rotation to get going. Once the motor is spinning the starting winding is disconnected by a centrifugal switch.

Two-phase is also preempted in the world of motors but a bit more obscure. Two-phase motors are induction motors where two windings are driven in quadrature (90 degrees out of phase). These were used as servo motors at a time but, I believe, have largely been supplanted by DC motors of various kinds (brushless, brushfull, permanent magnet, etc.).

So what to call it? How about "Edison system" or "125/250" or "3-pole (4-wire) single-phase" like in the plug catalogs? Thinking about it, 3-pole single phase sounds pretty good and is only a little awkward.

Best,

--Frank

[Steve M Smith]

I think Mike is just going through a phase.

Is that like the guitarist who goes to the doctor because his voice is sounding strange, who gets told "don't worry, it's just a phaser you're going through"?


Steve.

[Mike Sokol]

Is that like the guitarist who goes to the doctor because his voice is sounding strange, who gets told "don't worry, it's just a phaser you're going through"?

I was pretty sure this topic would bring out both the best and worst comments. 

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