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Pulling hair out over 3 phase

12/28/14       
Andy

I have a single phase shop with four 230-240V machines. I am about to receive a three phase 220V CNC.

Part of me just wants to get a good rotary phase converter to run the CNC and be done with it, but the power company has offered to run three phase to my shop for free. The problem is that will put my 230-240V machines on 208V, and I don't like that.

I have read and researched until I am blue in the face, and I still don't know what to do. I'm not planning on buying more three phase equipment, but you know how that goes. I just need a reliable and affordable solution.

12/28/14       #2: Pulling hair out over 3 phase ...
Jon Member

You will still have 240v single phase when you get three phase. You will have the same two 120v legs that are 120v to ground and 240v from each other, and the third power leg will be 208 to ground. All your existing machines can be run the same as they are now.

I would strongly encourage you to get the three phase from the power supplier. I'm not sure that the third phase generated by the converter is of the same quality as what the power company will supply. As I remember, the phase shift depends on the load on the converter. Others can confirm or deny this. And I can tell you that you want a good reliable power source for your router. Small changes in voltage will cause problems.

I know you say you won't be adding any 3 phase equipment, but I bet if you have it, you'll use it more at some point. One real advantage is running a 5hp motor on a 20amp circuit. Less amps equals less heat equals forever motor and component life.

12/29/14       #3: Pulling hair out over 3 phase ...
Russ

Website: https://www.mirror-reflections.com/

Andy Phaze Perfect is a possible solution, I bought mine (PT-330) about three years ago and have solved all my electrical problems. The name says it all, three perfect, stable legs of power. I have two profile grinders, the manufacturer has tightened up the range of power fluctuations, it used to be + or - 10%, but they are now in the range of 6-7 % As stated above its critical to have stable legs of power with frequency inverters and other finicky electrical controls. In fact the owner of this company started this company because he could not run his cnc machinery with what he had available at the time . But... they are expensive, and you have to weight the fact that free three phase power from the electrical company vs paying for one of these units. I could not load Phaze Perfect website, but I found this one below that should help you get started. Made in the U.S.A is a bonus.

I researched mine for months, I previously owned a rotary converter, it worked well until the manufacture changed the tolerances on my frequency inverter which controls the speed of my motors. Good Luck Happy New Year Russ @ MR

Phase Perfect Digital Phase Converter

12/29/14       #4: Pulling hair out over 3 phase ...
David R Sochar Member

Get your 3 phase from the power company. Then contact the maker of the CNC to see what type of transformer you need to run the machine safely, with no compromise, on the power as supplied form your utility.

If in doubt, contact an electrical contractor and ask for a quote. Contact 3 if you want to be sure.

I have had my electrician find and install shoe-box sized transformers on several machines over the years. It is inexpensive, safe and easy.

While I also have experienced serious hair loss, that was not the cause.....

12/29/14       #5: Pulling hair out over 3 phase ...
Bill

Go three phase for sure. We are 208 and have no problems with 240 equipment.

A good CNC should come with a transformer.

12/29/14       #6: Pulling hair out over 3 phase ...
Andy

Thanks for the advice, all. I will be going with the power company three phase. I've heard good things about Phase Perfect, but it's a bit steep, considering I can get the real thing.

For those with three phase, do you have separate load centers for your three and single phase breakers, or do you run everything off the three phase load center? I have seen where it can't be done, as long as you don't use the high leg (or B line) for any single phase circuits.

Seems like it would be easiest to rip out the single phase load center and put in a three phase center to use for both. I'm just not sure if that is kosher. I don't have to worry about code inspectors where I am, but I don't want anything unsafe.

12/29/14       #7: Pulling hair out over 3 phase ...
Andy

Is it possible that I will need a buck transformer to get the 240v down closer to 220v for my CNC?

12/29/14       #8: Pulling hair out over 3 phase ...
JeffD

If they'll run it for free there's really no decision in my mind. You have to go with 3 phase from the power co..

As for panels I've used 2 different systems in shops. My last shop had separate single phase and 3 phase panels. In that shop I was getting something like 240v from the 3 phase panel. In my new shop I have both coming from the same line. This provides 208 volts for the 3 phase. Only a couple newer machines need to have the overloads adjusted for the lower voltage. Though I am still having trouble with an older CNC that may be voltage related:(

Anyway point being that either way should work fine for your equipment. If they happen to leave the original panel as is and just add a separate 3 phase meter though that would be the ideal for your situation.

good luck,
JeffD

12/29/14       #9: Pulling hair out over 3 phase ...
Jon Member

Remove your present load center and replace with a 3 pole load center. I use Square D. The breakers are available almost anywhere. Every third space will be the 208v leg. The other spaces will be exactly the same as what your previous panel voltage was...should be 120-125 v to ground, and 240-250v between them. So when placing single phase breakers, just skip that third space. You can always add another panel with 3 lugs and no main if you run out of spaces. I put a 100amp 3pole breaker in my main panel and feed a second 3 pole panel with lugs and no main to gain additional circuits.

As far as the buck transformer to reduce the voltage, that will depend on what your voltage readings are from the power company. You should have the close to the same voltage when tested across any two of the three power legs. Mine reads 230 - 235v between any two of my power legs. The tech that installed my router said I was on the edge of needing a buck transformer to reduce the voltage. You will need to discuss this with your tech after you get your power into your panel, and test the voltage. I opted to not use a transformer, and have had no issues.

12/30/14       #10: Pulling hair out over 3 phase ...
Joe Calhoon

Running it in for free sounds like the way to go. I would check to see if they put you on a demand meter when they do this. That would be a deal breaker for me depending on demand rates.
Joe

12/30/14       #11: Pulling hair out over 3 phase ...
JeffD

Something about the previous posts sounded funny so before saying anything I went and checked my power today. If you test between any 2 leads on my system you get 208v, (+/- mine actually runs a bit low), but not 240v! Any single lead to ground pulls about 115v with one high leg that pulls closer to 125v. So maybe there are still different systems in use in the states?

Anyway just wanted to post as something you may want to check out and know beforehand…..though I'd still go for the 3 phase every time.

good luck,
JeffD

12/30/14       #12: Pulling hair out over 3 phase ...
Jon Member

I have had two different power suppliers over the years and both were the same, 1 "wild" leg 208v to ground (mine actually runs 218v), and two legs that act like single phase 120v to ground and 240v between them. I am in Indiana. The differences may be in the way that the power company gets the third leg. I have fried a contactor transformer or two over the years by hooking up the wrong leg.

You need to find out what yours will be. 208v will be a little low for you existing 240v motors. Will probably work, but I would get some advice from a professional. Remember volts and amps are inversely proportional.

12/31/14       #13: Pulling hair out over 3 phase ...
Bill

I am not expert but I would put a transformer. The CNC manufacturer will specify a voltage range that you definitely want to be within.

There are other benefits to a transformer such as leveling out the voltage.

1/5/15       #14: Pulling hair out over 3 phase ...
B.H. Davis Member

Jon's experience is interesting but not what I've experienced. I've always found 208 between any 2 legs of a 3 phase service and 110 to 120 between any leg and ground.

My old rotary converter used to give me one high leg that I had to be careful about placing on a motor or electrical controls.

There are different methods of producing 3 phase power so that could explain the different readings from various posters here. I will forward this thread to an industrial electrician friend who is very knowledgeable in these areas to see what he says.

All that aside I've never had a problem running 230v or 240v motors on 208v 3-phase. The motors do have a voltage range tolerance.

BH Davis

1/5/15       #15: Pulling hair out over 3 phase ...
B.H. Davis Member

Ok.........I've had a long conversation with my friend Neil the electrician. He been doing industrial wiring his whole life. He wires such outfits as Frito-Lay and independent small hydro plants and is an authority on electrical theory. I'm lucky to have him as a friend. His crew has done jobs for me but more importantly he has taught me more than I'd ever expected to know about electricity.

He read through the thread and said there is truth in what everyone had to say. However there was also a lack of understanding as to why they were seeing those results. I'll try and write out what he explained to me.

There are two types of 3 phase power in the US: Delta and Wye. The Delta is a 3 wire system that uses a separate ground wire to create 120v power. The Wye is a 4 wire system with the 4th wire being a neutral.

The Delta system is what Jon has experienced. You have 240v between any two of the three legs and 120v between either one of 2 of the legs and ground. The third leg though gives 208 between the leg and ground. That is why every third breaker in the 3 phase panel is a single wire 208v circuit. This, as Jon has discovered, can lead to costly installation errors. Neil started to give me an elaborate explanation of this 208v leg being the result of an angular vs. algebraic calculation but that was getting a bit beyond a phone conversation explanation so I told him not to try and explain it further.

Delta 3 phase would not be considered the preferred system for a typical installation. However you take what the power company has to offer. While Neil knows the Delta system is still in use in the US he did not know of the geographical locations.

Here in CT (at least our northeast corner of the state) the Wye system is supplied to 3 phase customers. With Wye power you have 120v between any single power leg and the neutral wire of the 4 wire system. Then between any pair of the 3 legs you have 208v.

Neil suggested that Andy ask the power company if they are providing Delta or Wye. If he has a choice then request Wye. If Delta is the only option he feels you'll still be better off than with a rotary converter.....you just have to be very careful when wiring circuits into the panel to make sure you don't pick up that 3rd leg that is 208v instead of 120v to ground.

As to 208v for your motors he agrees with those that have said it is fine for your 240v motors. I know I've been running that way for years without a single issue on a 240v single phase motor.

He also said that while you don't plan on buying any more 3 phase machines don't count on that being the case. 3 phase motors are less expensive and provide increased torque over single phase motors, thus making them the preferred choice when new machines are considered down the road. The main advantage to buying single phase motors in those situations is ease of selling to a wider customer base.

BH Davis

1/5/15       #16: Pulling hair out over 3 phase ...
Andy

Thanks again for the input.

I will be going with the power company 3 phase. I purchased a 42 space 3 phase load center and will use it for both the single and 3 phase circuits in my shop. I'm pretty sure the service will be a wye-type.

I am still considering a transformer to dial in the voltage, but I don't understand how that works, either.

2/10/15       #17: Pulling hair out over 3 phase ...
Jim Lewis

The easiest way for me to understand this stuff is by drawing vectors. If you use mm the lines are reasonably long, 1mm=1volt. With Wye (also called Star) the ground is in the center and the hot legs are at 120° to each other. With Delta, draw a triangle and center the ground below the top point. Measure the distance between the connections to get the theoretical voltage.

Think of the electricity as the power in a bicycle, and for Star/ Wye it has three pedals. The same way the pedals go up and down, the voltage goes positive and negative.

Using this metaphor, single phase is a bike with two pedals. There are spots where simple pressure on the pedals won't start the wheels turning. Hence, single phase motors employ tricks like capacitors to move the phase during starting— essentially, making a bike with four pedals. With three phase, you always have a leg that can efficiently turn the crank.

Beats me how to translate this to Delta. We don't have it in my part of upstate NY, so I never had to deal with it.

If you are set on stepping up your voltage to true 220/230/240, you generally use a transformer that will boost the voltage 10% or so. Sometimes they come with multiple taps that give you several choices.

If you don't step up the voltage, you have to compensate on the heaters of a mechanical motor starter. I'm not sure about the electronic ones, they weren't around when I wired my shop. I believe they might have dials to adjust precise cutout amperage. The point is, if you have lower voltage you'll use higher amperage.

If your electrician can't figure this out, you need a better electrician, one who handles industrial applications. It just doesn't crop up in residential, unless you are talking the Hearst Mansion.


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