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 have never ran across 120/208 3 wire system as a single phase... if I did run across it, I would probley be calling the power company wondering what was up....:confused:
 
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.

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.
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Maybe this is an open delta corner grounded?
 
This is a Trick question from point of view. The 208v if from utilities originated from a 3 phase system. IMHO the one that meter's two ungrounded wires feeding a PNL and reads 208 phase to phase will logicly determine 1 phase.But from what source did the EMF originate? 3 phase or single? It's the same as saying. I installed a Buck boost Xfer from a 3 phase supply it's now single phase cause i'm only using two legs. Now that baseball has started it's hard for me to focus. lol
 
frenchelectrican,

I believe hardworkingstiff has left us hanging bro. We have been disenfranchised. :grin:
 
mivey said:
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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I've always called it a "network". and I just thought I was being clever. :grin:
 
hardworkingstiff said:
There has been a lot of intense discussion about 208/120-volt "single-phase" service. What do you think?
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Your referring to this as premises, "What is a 3-wire 208/120-volt feeder to a meter base?

I think you mean service-entrance, and if I take this literally "what is a 3-wire 208/120-volt service entrance to a meter base? I'd say the service-entrance is single phase.
 
LarryFine said:
After all, what do we call it when a 3-phase motor loses a phase?
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208 L1-L2 is definitely single phase. There is only one possible current flow to the load so this current is in phase with itself. This is the case with a single-phasing three-phase motor. But in that instance, we aren't involving the neutral conductor.

But 208 L1-12 and L1-N and L2-N can create three distinct and seperate out of phase currents. And three distinct and seperate currents, all out of phase with each other looks like 3 phase to me.

I still won't argue with the IEEE definition of it being single-phase.

And, I am not even sure if you would call the "neutral" of that 208 system a neutral. It definitely carries more than the unbalanced load.
 
crossman said:
...208 L1-12 and L1-N and L2-N can create three distinct and seperate out of phase currents. And three distinct and seperate currents, all out of phase with each other looks like 3 phase to me...
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Where is the 3rd phase?
 
Karl H said:
I've always called it a "network". and I just thought I was being clever. :grin:
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You were just ahead of your time. Mort de Rire (for you Marc)
 
mivey said:
The "bowstring" neutral
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I'm not sure what "bowstring neutral" is but in this case the neutral would not be a supply phase like one of a three-phase system, rather it is a return [phase] grounded conductor??
 
No way no how can anyone convince me that 2 xformer windings 120* electrically out of phase can be considdered single phase. It is not so get over it.
 
ultramegabob said:
I have never ran across 120/208 3 wire system as a single phase... if I did run across it, I would probley be calling the power company wondering what was up....:confused:
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Lots of it in my area. They call this a "network service". They run all three phases around at distribution voltages, and just jump off here and there with single phase to each building (or 3-phase, if you need it). Lets them put one large transformer somewhere out of the way. These network services (often called network loops) are typically double end fed, to allow sectionalizing a part for service without taking an outage for everyone on the network.
 
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tryinghard said:
Where is the 3rd phase?
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Phase or line? My point is that we can have three distinct and different and out of phase currents flowing from the given voltage source/system.


00three-1.jpg


For example:

1. There is a current which flows from B through Load 1 to N.
2. There is a current which flows from N through Load 2 to A.
3. There is a current which flows from A through Load 3 to B.

There are three load currents. Each individual load current is out of phase with the other load currents.

The current in each conductor is out of phase with the current in the other conductors.

There is a rotating magnetic field produced at the three loads.

A standard three phase motor squirrel cage motor will start and run with this system. (granted, it will not run with full efficiency and HP, however see the next sentence)

We could design a "three phase" motor which would run perfectly fine on this system.
 
tryinghard said:
I'm not sure what "bowstring neutral" is but in this case the neutral would not be a supply phase like one of a three-phase system, rather it is a return [phase] grounded conductor??
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It is a neutral point that is not on a vector line drawn beween the two conductors V1 & V2. Since this reference point is shifted away from the V1-V2 vector, the path drawn from V1 to N to V2 is no longer straight (like in a 120/240) but has a "bow" in it (see crossman's picture). This offset neutral reference gives us the angle we need to create rotation.

mdshunk said:
...They call this a "network service"...
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I guess sloppy wording caught up with me again. We should use the term "3-wire network service" when referring to the 3-wire 120/208 service. I think this is different from the network you were referencing.
 
e57 said:
Which calculation method would you use - single phase, or 3 phase serving single phased loads?
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Could you please describe these two calculations and/or what you see to be the difference in these two calculations?
 
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