single-phase?

single-phase?

  • This is a single-phase service.

    Votes: 26 49.1%

  • This is part of three-phase service feeding single-phase loads, and not actually single-phase.

    Votes: 27 50.9%
  • Total voters
    53
  • Poll closed .
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I want to answer 'both' :)

It _is_ a 'single phase service' by the definition of a single phase _service_.

But it is not true single phase power being delivered to that service.

-Jon
 
Can I directly run three phase equipment from this service?

No, because it is a single phase service supplied from a three phase source.

In other words I agree with Winnie and really wonder what all the hubbub is about.

To try to call it a three phase 'service' is IMHO ridiculous.
 
I like jon's, zog's, bob's answers - all good

IEEE 141 refers to NEMA C84.1, which calls it a "208/120 open Wye". I didn't see anything in IEEE 100.

carl
 
With only two ungrounded conductors and the neutral of a 208Y/120 3phase 4wire system, we can take two single phase transformers and create three phase.

The IEEE may call this single phase (and I don't neccesarily disagree with them). But, with single phase 240/120 3 wire, the neutral only carries the unbalanced load and doesn't have to be counted as a current-carrying conductor. This is not true of the 208/120 system with 2 ungrounded conductors and a grounded conductor. The grounded conductor has to be counted as a current carrying conductor because the loads do not balance.
 
winnie said:
I want to answer 'both' :)

It _is_ a 'single phase service' by the definition of a single phase _service_.

But it is not true single phase power being delivered to that service.

-Jon
Click to expand...
Winnie, why don't we just use the terminology that EEI uses for metering and call a 120/240 a single phase service and a 120/208 a network service?

[edit: Marc, you just did beat me to the finish line]
 
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iwire said:
IMHO you did.
Click to expand...

I guess you could look at it this way, but.....

A building contains walls, floors, roof, etc. Would you call the walls and floors a building (leaving the roof out)?

I did not mean to say that 2-phases of a 3-phase system would constitute a 3-phase system, nor do I believe I said that (I think it's what you expected I would say).

I also do not believe it is a single-phase system although it is allowed to serve single-phase loads.

I now believe this is a topic that will never have consensus and I intend to leave it alone (I hope, I have said this before, lol).
 
crossman said:
With only two ungrounded conductors and the neutral of a 208Y/120 3phase 4wire system, we can take two single phase transformers and create three phase.
Click to expand...
Yep. The power company does it all the time, and calls the secondary an open Delta.

But, with single phase 240/120 3 wire, the neutral only carries the unbalanced load and doesn't have to be counted as a current-carrying conductor. This is not true of the 208/120 system with 2 ungrounded conductors and a grounded conductor.
Click to expand...
Then the question is whether neutral cancellation is a characteristic of single phase. I say not.

After all, what do we call it when a 3-phase motor loses a phase?
 
I'm not sure about the the single/dual phase argument but I do know that all the 208 I've ever seen came from Y-connected three phase transformers. The 208 is the phase to phase voltage. 117 is the phase to ground/ center tap of the transformer. (117 x sq. rt of 3=208)
 
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