# how common are 240v 3ph sources in the US? (electrical system history discussion..)



## Electric_Light (Apr 6, 2010)

It's just my guess, 277v is a byproduct of 480v where 480 was chosen as the "standard" voltage.

415v in Europe, I think is a product of designing around the 240v ph-N as the "standard" voltage. Just like our 208/120 where the need to serve 120 in commercial application was chosen over a system centered around 240v motors and provide 240v/139v system. 

Meanwhile, in Canadia, they went on their on their own tangent and still use 600Y/346v system. 

So... why are 3ph motors usually primarily designed for 240v service?


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## RePhase277 (Feb 5, 2008)

A delta service does good with motor loads, so since 240 volt single phase was standard, it kinda makes sense to have a voltage where you can use single and 3-phase motors. A 240 volt delta can do both.

And if you center tap one phase you can get 120 volts too, so it is a win-win service if you have alot of motors to power. I have noticed that, at least around here, they don't seem to install many new 240/120 V delta services.


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## retiredsparktech (Mar 8, 2011)

InPhase277 said:


> A delta service does good with motor loads, so since 240 volt single phase was standard, it kinda makes sense to have a voltage where you can use single and 3-phase motors. A 240 volt delta can do both.
> 
> And if you center tap one phase you can get 120 volts too, so it is a win-win service if you have alot of motors to power. I have noticed that, at least around here, they don't seem to install many new 240/120 V delta services.


According to our Poco's metering manual, 240 delta is NLA for new installations. They will support existing services.
They're really pushing 120/208 and 277/480 for new installs.
Look up your local Poco and see what they offer.


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## ampman (Apr 2, 2009)

about 60% of the services i work on are 240 v delta


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## retiredsparktech (Mar 8, 2011)

ampman said:


> about 60% of the services i work on are 240 v delta


One plant I spent 20 years as an electrician, was 240V corner grounded delta. 
There were several different parts of that plant, built over the years. We owned our own transformers, so we weren't held to the Poco standards.


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## McClary’s Electrical (Feb 21, 2009)

retiredsparktech said:


> According to our Poco's metering manual, 240 delta is NLA for new installations. They will support existing services.
> They're really pushing 120/208 and 277/480 for new installs.
> Look up your local Poco and see what they offer.


 
I can still get up to a 200 amps from Dominion in some locations.


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## Bulldog1 (Oct 21, 2011)

We have a few areas here where they are common. One poco will still provide one up to 400 amps. Someone else said they work well with motors and that is exactly why a lot of old factories here had them.


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## Electric_Light (Apr 6, 2010)

The permissible 120v load is very small on 120/240 delta. I don't know the exact percentage though.


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## frenchelectrican (Mar 15, 2007)

Electric_Light said:


> The permissible 120v load is very small on 120/240 delta. I don't know the exact percentage though.


 
It depending on which type of transfomers and conferation it used.

If single three phase transfomer with centre tap some are limited to 5% of total KVA rating without getting overloaded or get it out of balance otherwise the common three indivual transfomers useally the best if you know the proper connection to get pretty good load capacity.

Merci,
Marc

Oh by the way in my POCO area in Wisconsin ( WPS ) 3 Ph Delta is NLA either only on exsting installment but may allowed to upsided to match the main breaker rating but nothing more only on exsting installment.

In France the Delta system is very limited as well most resdential and commercal use wye format.


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## Jerome208 (May 10, 2013)

Here in PG&E territory, all small services are two-can, open delta, 120/240, with the lighting pot much larger than the kicker. I thought that was the only way until I began reading about what other parts of the country do. I suspect it is because PG&E is a *very* old company and set in its ways.

They will serve larger loads with 3-bushing transformers which I assume are usually wye but I haven't measured them all. Either 208 or 480.

It is very rare to see 3 pots on any pole here, except for some very old installations and they are still usually 120/240 delta with the center pot much bigger. But there is the occasional 3-pot wye service.

Just to give some idea of how things are done differently.


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