Single phase or three phase?

No, I've got several true RMS meters (Fluke 87V, Agilient U1252B) and they all read 120v/240v with a volt or two. If you're reading 220V, that's at the low end of what the utility should be delivering.

Away from the panel, you can get some voltage sag if there's heavy loading on the line.

What everyone said above about phases and legs. Nominally the US 240VAC lines have two phases, but since they are 180 degrees apart, you can't use them to start a motor directly. There's a dead spot and no preferred direction.

It's not really a summing issue. If you sum all three phases together from the power company you'd get 0V, too. That's not true with RPC power, since two phases come directly from the mains. The generated third phase (wild leg) is 90 degree apart (relative to ground) and the vector sum of the three winds up at 120V * tan 30 ~= 70VAC.
 
If you plant o have multiple three phase machines then a rotary phase converter feeding a three phase breaker box with a three phase circuit breaker and circuit running to each machine is what I would suggest.

Below is a photo of my RPC/three phase set up with only one machine installed (Icurrently have four three phase devices). Left side is my single phase breaker box. On the right is my three phase RPC idler on the floor running up to the phase converter I built which feeds the three phase breaker box. In between the single phase breaker box and the three phase system is a cut off switch/isolation switch to the three phase setup.

This set up will allow me to add to more than the four existing three phase devices.

Vlad


RPC Wall.JPG
 
Times may have changed but I wonder about the economics of grid 3 phase power. Here in the farming community I am given to understand grid three phase is more expensive than single phase. It seems that "power factor" has to do with the electricity cost and availability to the grid source and I believe single phase is billed by electrical power used. I stand ready to be corrected on this subject.
Have a good day
Ray
 
As far as initial installation cost 3 phase is more expensive. As far as power usage (at least in this area) everyone is charged by the kilowatt hour used, plus a "demand charge". The demand charge is larger or smaller depending on the size of the service installed. The larger the potential current draw the larger the demand charge. Then comes the "volume discount rate". Once you reach a certain usage level the price per kilowatt hour is reduced substantially.

I have seen instances where a homeowner with a 300 amp, 220 volt single phase service is paying more than a commercial shop with a 300 amp 3 phase service. They both pay a similar demand charge, but the commercial shop is actually using fewer kilowatt hours because the 3 phase machines draw less amperage than similar sized single phase machines.

I doubt you'll ever see 3 phase power go away. The largest 220 volt single phase motor I am aware of is 50 hp. More realistically 10 to 15 hp is the maximum that could be used in a residential setting. There are 220 volt 3 phase motors that put out as much as 250 hp. The most extreme hp units I've seen are made by Baldor. They have some up to 15,000 hp, but don't try to run one unless you have a 13.2 KV power supply available.

When we built our current house I tried to get a 3 phase service for running shop equipment. The power company was happy to do it if I was willing to pay to have it extended from the nearest available connection. Unfortunately the nearest connection was a little more than a mile away. The cost was prohibitive in that had I run every machine I had at the time 24/7/365 I would never been able to recover the installation cost.
 
Here in New York City, it is now common for residential homes to get 3 phase power, mainly to run central air-conditioning and sometimes elevators as well.
 
Having seen a surface grinder , yes the same machine run on true 3 phase and a phase perfect generated 3 phase coming from single phase source, the machine gave better surface finish and ran quieter and smoother on the phase perfect. I don''t know how or why that is, but having seen it with my own 2 eyes, they are the real deal. If surface finish is not a big deal, I would go with static or VFD. I ran a Clausing 5 hp machine on a 4-8 hp rated Heavy Duty static for years and it worked fine with very nice surface finish.
 
I bought a used 5hp rotary phase converter in 1998 . This converter runs a 13” LeBlond servo shift,a step pulley Bridgeport,a 6x18 Reid Brothers surface grinder , a 10” pedestal grinder ,and a 20” heavy duty Cincinnati shaper . I needed 3 phase because all these machines came equipped for it .
The rotary phase converter cost $450 plus wiring and disconnect panel . The surface grinder has a small motor so I balanced the high leg with a transformer .
The converter is a little noisy so I mounted it above the insulated ceiling . Not bothersome after that .....Steve
 
Mans Racing said:
Well I decided to go with a 3 phase unit so I ordered a PM1440GT Lathe.Im just going to start out with a static phase converter then at a later date when I have the time I will install a VFD.Even at 2/3 power to start with it should be just fine.I was just concerned about how smooth it would run with single phase vs three phase. Thanks for all the response and help on this matter.Being very inexperienced in being a machinist I’m sure glad I found this site.
Thanks
Click to expand...

I used a static phase on my mill that I purchased because it was the simplest solution


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Another vote for 3 phase. My first 3 phase machine was before I had line 3 phase. I made a rotary converter from a 3 phase motor, some big electrolytic caps and a couple of switches. Ran for years that way. A minor catch is your machine won't quite have the same amount of power. 3 phase motors are way more durable/reliable than singles. I now have 800A 3 phase service but my electrician says I'll need to add more if I want to run additional equipment. You can run 50 cycle motors on 60 but not recommended to go the other way.
 
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