Need 3 phase Assistance

[Matt Hutchinson]

As I am doing research into wiring 3 phase circuits, I keep coming up short. I mean, things are still a little hazy, and I would love help nailing down the details.

1.) Assuming I am using 10 gauge wire, do I need 3 conductors and a ground, or do I also need a neutral? For some reason I seem to be getting mixed messages in this department. (Or I am just misunderstanding.)

2.) What's the least expensive way to get power to the four 3 phase tools. Meaning, how do I connect four loads to the one power source with the least expense? Do I need a 3 phase load center, or do i just run all the tools into one junction box and feed it directly from the converter?

3.) Do you have any pictures of your 3 phase wiring/circuits?

Thanks for any help you can give!

Hutch

[Travis Porter]

I am not an electrician, so you get what you pay for.

1. 3 conductors and a ground. That is the way all my 3 phase tools are laid out.

2. I daisy chained the outlets just like you would do for single phase outlets. I want a 3 phase load center, just haven't found one cheap enough for my budget.

3. Sorry, no pics. I come out of a phase converter and go to twist lock 3 phase receptacles. The receptacles and plugs gave me sticker shock!

[Matt Hutchinson]

Yeah, same here. I went to price out the plugs and just about had a fit. Did you use twist lock plugs? I was told there wasn't any other kind available for this type of setup, and that means about $60 per tool just for the stinkin' twist locks!! Did you find any bargains?

Ok, so what you are saying makes a lot of sense. I think I am in a similar situation, not being able to find an affordable load center and all. So I think I will proceed to plan the receptacles in series, like you said.

Cool Stuff! Thank you!

Hutch

BTW, did you run the circuit yourself?

[Rob Russell]

When I was looking for 3-phase stuff, I found Ebay to be a good place. Just be patient and you can pick up great deals on plugs/receptacles. You can also find a good load center cheap.

For my equipment (Felder), I needed 3 hots + ground, but also a neutral because there are some 120v control circuits in the machinery control panels. That's not going to be normal.

It's wise to put a load center between your machinery and the phase convertor. That way you can size the circuits to the machines.

[Rick Christopherson]

First, the easy answer. Not only do you not need the neutral, but because this is coming from a phase converter, you CANNOT use the neutral under any circumstances. Regardless how the motor is wound internally (delta versus wye) you NEVER connect the neutral to a motor!!!!! (And that holds true regardless whether it is true 3-phase or generated 3-phase, but it becomes absolute when dealing with generated 3-phase.)

Secondly, 3-phase power uses a lot less amperage per horsepower than single phase, so it is not very likely that you need #10 wire. #10 wire is for 30 amps, and at 3-phase, 30 amps gives you 11 to 12 horsepower!!! Anything less than 5.5 horsepower at 3-phase can be run with #14 wire, and #12 wire will give you up to 7.5 horsepower.

If you are powering several tools from the same converter, then it is probably in your best interest to use a small 3-phase load center. I think you could do this with raw terminal blocks, but it is not the best solution. Oh, as I see Travis pointed out, daisy chaining outlets is fine too.

I prefer the load center because you would bring in the two house phases separately, and only the generated leg comes from the converter. There are a lot of ways of doing this, but this is the most straightforward.

[Rick Christopherson]

For my equipment (Felder), I needed 3 hots + ground, but also a neutral because there are some 120v control circuits in the machinery control panels. That's not going to be normal.

This is a special case because those control circuits are single-phase, not 3-phase. It should be pointed out that when you do this, you are actually taking the original single-phase house power to accomplish this task, and it is independent from the phase converter (even if you think it is going through the converter, it is not).

[Matt Hutchinson]

Aaaahhhh, I love the information age.....

So the largest tool I have is an old 5 hp, but it's 440V at this point. I am going to take it to a motor shop to re-lead it (for 230V), and if that doesn't work, I will have to have it rewound. So, without running out to the shop to check its amperage, I may need 10 gauge for that one tool....maybe. But great to know that I may only need 12. Any way to shave off a few dollars here and there is helpful.

And the clarification of the neutral helps a lot too.

The more info the better. Thanks so much!

Hutch

[Bruce Page]

Matt, do you have 3 phase coming into the box? If not, are you planning on using a converter e.g. static, rotary, vfd?

[Rick Christopherson]

So the largest tool I have is an old 5 hp, but it's 440V at this point. I am going to take it to a motor shop to re-lead it (for 230V), and if that doesn't work, I will have to have it rewound. So, without running out to the shop to check its amperage, I may need 10 gauge for that one tool....maybe.

At 440 volts, a 5 hp motor only draws 7 amps. It is a common misconception that the higher the voltage, the larger the wire needs to be. This is not correct. The size of the wire is only dependent on the amperage. If this is your biggest motor, then all of your wiring can be 14 gauge.

However, don't confuse this with the requirements on the line-side of the phase converter. Your phase converter supply wire needs to be larger than the output wire.

[Matt Hutchinson]

Actually, I am still planning on using 10 gauge wire into the converter. But what I meant about the 5 hp motor was that switching to 230V would double the amps, but if it's 7 amps to begin with, then it's irrelevant anyway.

Bruce, I am going to be using a 10 hp rotary converter. (I chose to go much larger than I need right now cuz it wasn't much more expensive, and I may want to run multiple tools at once down the road.)

Hutch

[Thomas Syrotchen]

Matt,
I'm not sure if I understand your response below about the 7 Amp or not. If you use a higher voltage on a motor then the current will be reduced. Most industrial stuff is run on 460V because it requires less current and hence a smaller conductor. There are other reasons before I'm quickly corrected, but it certainly one advantage of using the higher voltage. If you rewire a motor for 230V you will double the current draw for the motor and hence require a larger conductor. The nameplate on the motor should show two numbers for Full load Amperage (FLA) one for 460 and one for 230 if its a dual voltage motor. When sizing a conductor, you should read the FLA from the Nameplate, motors will vary on current draw based on a few factors not all 5HP motors will draw the same current and I come up with 8 amps at a minimum for a 5HP motor at 460V with no losses. 10 amp I believe would be a more realistic ball park figure when you account for the efficiency and power factor. If you wire it for 230V your looking at 20 amp ball park figure. Conductors should also be sized at 125% of FLA at minimum. I personally use 150%, it rarely is much of an increase in cost.

Depending on what your trying to accomplish with a "load center" there may be more economical ways of accomplishing the task. If your are simply looking to protect branch circuits, fuse blocks are normally the most economical way to go. If you looking remove power from a device and provide circuit protection, then fused disconnects or a fuse block and a local disconnect may again prove to be more economical. If your looking to distribute power in one box and provide circuit protection, then I'd look for a prebuilt box on E-bay.
My two cents on sticker shock, remember that your buying items that are built for industrial type uses that are usually built for a more demanding environment. I hate the prices too, but I haven't had to replace anything I've bought for home as well.

A few things you may want to keep in mind as far as running multiple tools at once.
Check with the manufacturer, but some size their converters using 746W/HP of power output based on the idler motor size with no loss. Since motors in the real world have loss, they use more power than 746W/HP. A 10 HP rotary converter may not handle two 5HP motors running. Now factor in that at start up a motor can draw up to 150% of it FLA and one can quickly overload a phase converter. It all depends on how the manufacturer list their size. Since marketing has a say, my bet is that 10HP converter may not have a lot of capacity left on it once you factor in starting that 5HP motor.

[Rollie Meyers]

Motors are quite different then normal branch circuits which means the ampacity can be used as listed in table 310.16 if conditions are met per art. 430 of the NEC. BTW, this means 14 AWG is rated for 20 amps, 12 AWG is 25 A., read it carefully to apply the rules.

Article 430---Motors,Motor Circuits,and Controllers.

[Matt Hutchinson]

LOL! Tom, I guess I didn't really explain what I was saying clearly. I actually was trying to say what you just said. That is, if I were to take a 460V motor and convert it to 230V I would double the draw. That's why I said I didn't know if I would still need 10 gauge for that one tool, but I see now that 10 still seems a bit oversized.

As for the converter, I don't know all the details. It was built by a guy in New York under the business name WNY Supply. A number of fellas on a machinist forum said it was a good converter for the money, so I thought I'd give it a try. Running multiple tools on it is probably okay, because I only have one 5 hp machine, and the rest are 3 hp or less. But running multiple tools is not something that would happen often. Only if I had someone helping me with a project.

In an ideal world, I would have the machines breaker protected on their own circuit. But putting them on one circuit will get me started I think. Could you elaborate about the fuse blocks? Do you have a link to a pic?

Thanks everyone!

Hutch

[Thomas Syrotchen]

Matt,
If you go to WNY's website, they have a sizing chart. If I read it correctly, based on their sizing chart you would be limited to 7.5HP of total load on a 10HP converter to allow the starting of your 5HP load. In other words your 3HP load running and then trying to start your 5HP load may exceed the capacity of the converter. Likely your 5HP load will start, but at the same time your causing damage to the windings on the idler motor and ultimately shortening its life. Based on your 5HP 3HP I'd probably look at a 15HP unit. WNY though should be able to help you determine if you really need a 15HP unit. Obviously the other option is to run one machine at a time, or never start the 5HP unit with another machine running.

A fuse block image.
http://images.grainger.com/B282_27/i...MALL-4XF45.JPG

You could probably do fuse blocks for under $30 a machine, and maybe half that on ebay.

As Rollie pointed out, motor circuits have their own section of the NEC and for good reason as they place a much more complex load on a circuit than your average 60W light bulb. Correctly sizing conductor isn't as simple as saying I need 10 AWG or 12 AWG. I'd echo Rollie's comment, spend some time reading the NEC.

[Matt Hutchinson]

Okay, thanks for the heads-up (and all the other info)!

Sorry, please bear with me.

So, the fuse blocks protect the motors. If I chose to ran 10 gauge with a 30 amp breaker, the circuit would be way more than I need for most of the machines, but the fuse blocks at the individual machines would protect the motors while the 30A breaker protects the wire? (Just trying to make sure I comprehend the concepts.)

Hutch