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What do Americans mean by 'single phase'?

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DavidA:
Hi all.

I'm a bit puzzled.

When we in the UK talk of single phase we refer to one leg of the three phase system generated by the power supplier, and a neutral leg. which is, if I remember correctly, connected to the centre of the three phase 'star' at the generator.

So we have 240Volt (nominal) between each phase and the neutral line.  And 415 volt (nominal) between any two phases.

Unless specially requested (and paid for) we get use of just one leg and the neutral.

I have been running my 415 Volt three phase motors via a 240 to 415 transformer, then using capacitors to make the ghost phase.  It works, but not very satisfactory as the pony motor soon gets too warm.

However, I recently watched the video...



By sbirdranch 'Building a phase convertor (parts 1 to 3)'

I began considering checking if my motors are 240/415 Volt. And if so maybe I can run them as 240Volt. Saving the transformer and making the purchase of run capacitors a bit less expensive.

But then I got to wondering about the American supply.

I think they have three phase 120 Volt to their houses, and they obtain the 240 Volt by utilising two of the phases.

They don't appear to use the neutral line in this set-up as this would not give 240 Volt required.  I'm not altogether clear on this point.

I someone could take a few minutes and look at the link, then get back abs tell me whether or not I can use our normal single phase system in the same way, I would be very grateful.

(also, does this require the motor to be connected in Delta ?)

Dave,

efrench:
It's a phase most teenagers and young adults go through before finding a mate. :Doh:

WeldingRod:
We Americans have the thrill of getting access to a single leg feeding a center tapped 240 vac transformer, with the center tap grounded.  Like you, three phase service for houses is "bought and paid" dearly for, assuming it gets anywhere near your house.  Most of the runs down the street are a single leg!
Our small loads get 120 vac, and the big stuff goes across the full transformer output of 240.

Sent from my SAMSUNG-SM-G891A using Tapatalk

djc:

--- Quote from: DavidA on September 16, 2019, 06:06:10 PM ---...I began considering checking if my motors are 240/415 Volt. And if so maybe I can run them as 240Volt....

...tell me whether or not I can use our normal single phase system in the same way, I would be very grateful...
--- End quote ---

To answer the second part first, many urban areas in UK have a three phase cable running down the street and each home is fed alternately off one of the phases (i.e. house 1, phase 1; house 2, phase 2; house 3, phase 3; house 4, phase 1). So if you are friendly with the neighbours on both sides, you could borrow a phase of each of them and have 415v phase to phase. This is undoubtedly illegal and unsafe, but theoretically possible.

For the motors, start with the data plate. If it says 240/415v or has symbols resembling a Y and a triangle on it, then it should be easy. Three phase motors have three coils inside, so six wire ends. To give maximum flexibility of connection, all six ends need to be user-accessible. In most modern single speed motors this is the case, but in older ones, three of the ends are connected together (star point) and buried more or less deeply inside the guts of the motor.  If you have the time and inclination, you can dig out the star point, separate and insulate the three wires and bring them out for use.  In some motors, this is not too difficult; in others, it is all but impossible. The only way to find out is to open up the motor and have a look.

mattinker:
So we have 240Volt (nominal) between each phase and the neutral line.  And 415 volt (nominal) between any two phases.

Yes

Unless specially requested (and paid for) we get use of just one leg and the neutral.



But then I got to wondering about the American supply.

I think they have three phase 120 Volt to their houses, and they obtain the 240 Volt by utilising two of the phases.

They have 220 volt three phase, one phase and neutral providing the 110 volt out put.

You can't get 415volts out of the UK system from a single phase supply without a transformer.

If you have 240/415 motors, you can wire the "Delta" run the on 240 three phase which you can obtain through a phase converter or, alternatively, a VFD.

It is worth noting that for small sizes, VFDs are now very cheap, probably less than the price of your condensers! I recently bought one, postage included, for a 3/4 hp motor for £42!!!

Regards, Matthew.

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