# Two phase system



## Robbie Rob (May 14, 2017)

I am working on a building from the 1800s, it has what I believe to be a two-stage system. It has 3 wires with 3 fuses but one is a neutral. So from ground to A is 240V ground To B is 240V and ground to C is 0V but, from any leg to leg is 240V. 
My question is if I move this machine shop to a new location will these motors that are running on 240V 2 phase run on a 208V three-phase system? I am not that good with motors. I assume I would also have to check the starters and contactors in the control system. Any advice would be greatly appreciated thank you.


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## Robbie Rob (May 14, 2017)

*believe To be a two PHASE system


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## MDShunk (Jan 7, 2007)

corner grounded delta.

Unless you're working in Niagara Falls, Hartford CT, Philadelphia, or the textile regions of the Carolinas, you're unlikely to see two-phase in your life.


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## MTW (Aug 28, 2013)

MDShunk said:


> corner grounded delta.
> 
> Unless you're working in Niagara Falls, Philadelphia, or the textile regions of the Carolinas, you're unlikely to see two-phase in your life.


Most of the smaller services of that vintage serving manufacturing in my area were ungrounded delta. A few still remain.


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## MTW (Aug 28, 2013)

A time capsule machine shop.  What does this place produce?


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## MDShunk (Jan 7, 2007)

MTW said:


> Most of the smaller services of that vintage serving manufacturing in my area were ungrounded delta. A few still remain.


Functionally, it makes little difference in this case. He doesn't have a two-phase system.


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## MDShunk (Jan 7, 2007)

MTW said:


> A time capsule machine shop.  What does this place produce?


The lathes and punch presses are WWII vintage or newer. Not original to the building, but old enough just the same. Perfect size for the home shop guy.


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## MikeFL (Apr 16, 2016)

Awesome pictures!


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## 460 Delta (May 9, 2018)

The answer to your question, is maybe. If the 208 star you’re going to put it on is on the hot side, say at 215 or so it should be fine. Most of those were designed at a time when 220 was the voltage of the day. Updates may be for 240 though so some testing will be necessary.


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## Robbie Rob (May 14, 2017)

MTW said:


> A time capsule machine shop.
> 
> 
> 
> ...


 Small metal gasket. Making the same gaskets from the 1800s still going strong


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## Robbie Rob (May 14, 2017)

460 Delta said:


> The answer to your question, is maybe. If the 208 star you’re going to put it on is on the hot side, say at 215 or so it should be fine. Most of those were designed at a time when 220 was the voltage of the day. Updates may be for 240 though so some testing will be necessary.


 Thank you, most of the nameplates were worn off so it’s hard to tell what they were and what they could run on. I’ll have to do a little figuring out


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## AU Facilities (Mar 25, 2015)

MDShunk said:


> corner grounded delta.
> 
> Unless you're working in Niagara Falls, Hartford CT, Philadelphia, or the textile regions of the Carolinas, you're unlikely to see two-phase in your life.


 

Not True...... The university I work at (long island, NY) still has one building that has 2 phase 5 wire. I also believe there is still some in the village of Rockville center, NY which has it's own power utility.


Gary


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## JRaef (Mar 23, 2009)

Robbie Rob said:


> I am working on a building from the 1800s, it has what I believe to be a two-stage system. It has 3 wires with 3 fuses but one is a neutral. So from ground to A is 240V ground To B is 240V and ground to C is 0V but, from any leg to leg is 240V.
> My question is if I move this machine shop to a new location will these motors that are running on 240V 2 phase run on a 208V three-phase system? I am not that good with motors. I assume I would also have to check the starters and contactors in the control system. Any advice would be greatly appreciated thank you.


As MDShunk said, you don't have a "2 phase" system, you have a 240V 3 phase delta corner grounded system. Very common. In days of old it may have started out as an ungrounded delta system, because so long as it was supplying 3 phase loads, it was considered "more reliable". But over time the potential dangers of that became so apparent that the NEC required that you EITHER ground one corner, or install a "ground fault monitoring system", which meant spending money. So many people opted to just tie one phase to ground because it was cheaper that way.


If you move to a place that has 208Y120V, those old motors may not like it, or they may be fine, there's no way to tell in advance. But it's true that if they were old enough, i.e. WWII vintage, they were likely built as "220V" and can tolerate +-10%. So that makes them good down to 198V, which is 208V -5%, within a utility's allowable deviation. However if your Voltage Drop at the actual machine is already 3%, AND the utility drops 5%, you may be out of tolerance for the motors. You'll just have to do it and measure it when you get there. If it's too low, add buck-boost transformers.


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## varmit (Apr 19, 2009)

You have a corner grounded 240 volt delta, three phase system system. 

Most motors, but not all, can operate on 240 or 208. As Jraef said, it can depend on the actual voltage at the machines at each location. I have seem a 240 system where the actual voltage was 219 and a 208 system where the voltage was 223. 

Remember, a lower voltage will increase motor current and heat. These old motors are pre NEMA standard, so replacements could be a challenge and rebuilds expensive. It could be cheap insurance to add a boost transformer to have a 240 volt system.


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## MDShunk (Jan 7, 2007)

AU Facilities said:


> Not True...... The university I work at (long island, NY) still has one building that has 2 phase 5 wire. I also believe there is still some in the village of Rockville center, NY which has it's own power utility.
> 
> 
> Gary


I didn't make a statement that could be responded to with true or false. I said "unlikely", but thanks for playing along. The places I listed are historically places where you're likely to still find two-phase. In the rest of the country, it's quite unlikely. It's neat that you have a building still served with this vintage system.


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## AU Facilities (Mar 25, 2015)

MDShunk said:


> I didn't make a statement that could be responded to with true or false. I said "unlikely", but thanks for playing along. The places I listed are historically places where you're likely to still find two-phase. In the rest of the country, it's quite unlikely. It's neat that you have a building still served with this vintage system.




My apologies...... And not really that neat, it's a pain in the ass because most don't know much about it. We have managed to get rid of all the loads and are down to one left, the old freight elevator.


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## frenchelectrican (Mar 15, 2007)

AU Facilities said:


> My apologies...... And not really that neat, it's a pain in the ass because most don't know much about it. We have managed to get rid of all the loads and are down to one left, the old freight elevator.


Just of few of us left is still famuair with old school true two phase system I already dealt 3, 4 and 5 wire system it kinda a big headache if you are not aware how it set up. ( too many guys end up hook up wrong phase and blow the fuse pretty fast is most common one )


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