Residential Power

[SmokinJoeR]

There seems to be some controversy on the internet wherever I check on how 240 volts is brought into your house. Some sources say that the electrical output of the transformer on the power pole is a 3 wire single phase, or others say it is 2 single phase 120V that have 180 deg of phase difference. I know the transformer has a secondary that is center-tapped, but I could never get the clear answer whether or not its 240V/single phase and (2) 120V/single phase output or (2) 120V with 180 deg of difference between them.

Anyone know for sure?

Thanks!

 

[stevenal]

rbulsara,

I cannot see that I've misconstrued anything you've said, because you have stated it over and over above, rewording it each time. Here is what I heard, please correct me if my hearing is bad: A 120/208 three wire circuit derived from a 120/208 4 wire three phase circuit is properly called single phase because it feeds no loads at the component level that are not 2 wire single phase in nature.

I disagree with the above for the reasons cited in previous posts. I agree we are discussing semantics. I disagree that it is a game, since speaking and understanding the jargon is important in this field.

 

[rbulsara]

stevenal:

The jargon is used by electrical utility companies in the US and posted on nameplates of UL listed panelboards, so it is widely accepted and it means what it says, it is intended for single phase loads. You may not agree with all that, but that is what it is.

For the likes of you, the definition of a single phase source would be a source with single sinusoidal waveform of a given frequency. The translation of which is a two wire circuit.

 

[BJC]

Back to the first post- It says residential power not appliance, coffee pot, garage door opener etc.
They are except for dryers and ranges single phase two wire loads. The residential power can be two phase.

 

[stevenal]

BJC,

I'm not aware of any two phase services used residentially. Two phase is an archaic industrial service. See Davidbeache's description above and the FAQ I linked.

Single phase panel boards are commonly used on open wye systems. I expect their listing allows this. 208 V rather than 240 so insulation is not an issue. The only difference is in the meter base and meter which have five lugs rather than four.

An open wye open delta transformer can be used to convert an open wye service to full three phase, so it is not true that only single phase loads can be fed.

 

[BJC]

The attached link has about 150 residental units with 2 phase power. Put a s scope on the two hots in any panel and you'll see two sine waves 120 degrees apart.

http://www.bpr.com/localsearch_display.html?mls=RMLS&listingid=7060651

I know lots more.

 

[rbulsara]

BJC:

No one denied that.

 

[jghrist]

The attached link has about 150 residental units with 2 phase power. Put a s scope on the two hots in any panel and you'll see two sine waves 120 degrees apart.

The building is probably served by a 120/208 3Ø service, with two phases going to each apartment service. By convention of most utilities, the individual services are called single-phase 120/208 volt. This avoids confusion because the apartment service panelboards are single-phase panelboards and all loads are either 120 volt 1Ø loads or 208 volt 1Ø loads. It might be more properly referred to as two phases of a three-phase system because the service does not meet the IEEE definition of either a single-phase circuit or a two-phase circuit (see FAQ link in Stevenal's Aug 20 post).