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Old 05-08-2008, 07:54 PM   #1
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3 Phase Converter Wiring


Hello,

I just found this forum and I hope you guys can help me with a wiring question.

I have a 3 phase converter and I need a little bit help wiring it to my specific receptacle. I have wired a converter to a piece of machinery before but this one is a bit more difficult and I don't want to screw it up.

The outlet I have to wire is a NEMA L21-30. It's a 5 wire outlet. My 3 phase generator consists of black, red and blue (plus ground - no common). I know I can use the pre-existing ground but how about the common from the single phase (I think I can)?

Below is an image of the receptacle.



How I would wire it would be
X - Black (L1)
Y - Red (L2)
Z - Blue (L3)
W - Common
G - Ground (Existing Ground From Single Phase Power)

Would this be correct?

Thanks in advance for the help!

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Old 05-08-2008, 10:49 PM   #2
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3 Phase Converter Wiring


It would seem that your generator would require an NEMA L15-30 3Pole 4Wire receptical.

Is this the connector that is on the phase converter? If so you would not want to use the Common/Neutral as your generator does not require it.

KC

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Old 05-09-2008, 02:01 PM   #3
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3 Phase Converter Wiring


The outlet I posted a picture of is what the 3 phase converter needs to power. The power source for the 3 phase generator consists of 4 wires (2 hots, 1 common and 1 ground). So what I really need to know if (and I think I can) I can take the common from the existing single phase 220 line and use it with new plug. Also, does X, Y and Z look correct?
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Old 05-09-2008, 03:04 PM   #4
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3 Phase Converter Wiring


Quote:
Originally Posted by ideffects View Post
The outlet I posted a picture of is what the 3 phase converter needs to power. The power source for the 3 phase generator consists of 4 wires (2 hots, 1 common and 1 ground). So what I really need to know if (and I think I can) I can take the common from the existing single phase 220 line and use it with new plug. Also, does X, Y and Z look correct?
Since you are technically creating a second power source from the converter, you can't just take the neutral from the existing panel.

You would not get 120 Volts from the neutral on the single phase panel to either L1 - L2 or L3 from the phase converter.

If the device your connecting needs 208/3ph for the motor and 120V for control, then you could possibaly wire the motor with the converter and the control circuit separate from your single phase panel, but you can't do it in the same connector/recepticle. You would have to have separate circuits and plugs for each.

Hope this helps.

KC

Last edited by kencaz; 05-09-2008 at 03:06 PM.
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Old 05-09-2008, 04:24 PM   #5
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3 Phase Converter Wiring


Thank for the help KC.

Unfortunately, I can not use two power sources for the system since the motors and electronics are integrated. Here is a diagram of what I wanted to do but you are saying it won't work.

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Old 05-09-2008, 05:46 PM   #6
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3 Phase Converter Wiring


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Originally Posted by ideffects View Post
Thank for the help KC.

Unfortunately, I can not use two power sources for the system since the motors and electronics are integrated. Here is a diagram of what I wanted to do but you are saying it won't work.

I don't know of any easy way you could do it being that your converter does not have a neutral tap, I don't know where you would possibly get the 120V your machine needs from the phase converter.

Most equipment I have delt with uses transformers with 208/240 primary and 120v secondaries for the control circuits. This elimanates this sort of problem.

I don't know what else I can add...

KC
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Old 05-09-2008, 09:20 PM   #7
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3 Phase Converter Wiring


What type of phase converter is it? Basically, there are 3 types.

1) Static. This type is nothing more than a box with several capacitors in it. The two 240 single phase wires run into the box, one of them usually runs straight through and connects to one motor lead. the other one connects to one side of the capacitors, and on to another motor lead. The other side of the capacitors connects to the third motor lead.

2) Rotary. This type looks alot like an electric motor, without a shaft. Some of these are indeed motors, usually with the shaft cut off. There's also a box with a few capacitors in it, sometimes a starter as well. The two 240 single phase wires go to the rotary part, and also connect to two of the 3 phase motor leads. Another wire comes out of the rotary part, and connects to the third lead of the 3 phase motor.

3) Motor-generator. This type has a single phase motor which drives a 3 phase generator. These are pretty rare, most of them use a 3 phase 60 HZ motor driving a 3 phase 400HZ generator. Usually found in large airports, sometimes several hundred HP.

If yours is a static or rotary type, connect the two single phase lines to X and Y. The neutral goes to W. The generated leg goes to Z. The neutral is already grounded at the source, don't ground it again. You'll have genuine 120 from either X and W, or Y and W. The voltage from Z to W is theoretically 208, but in reality it'll be anywhere from 150 to 250, depending on the type and size of 3 phase load. Make sure that any 240 volt single phase loads (like control transformers) are connected to X and Y. The only thing connected to Z is a 3 phase load.

If it's a motor-generator set, you can get 120 from it only if the generator is connected wye. Not delta. You'll need to get into the generator, 1, 2, and 3 are the output leads, 4, 5, and 6 are spliced together. You'll have 120 from this splice to 1, 2, or 3.

I realize this is somewhat complicated, if you need more clarification, just ask.

Rob
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Old 05-09-2008, 10:57 PM   #8
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3 Phase Converter Wiring


Quote:
Originally Posted by micromind View Post
If yours is a static or rotary type, connect the two single phase lines to X and Y. The neutral goes to W. The generated leg goes to Z. The neutral is already grounded at the source, don't ground it again. You'll have genuine 120 from either X and W, or Y and W. The voltage from Z to W is theoretically 208, but in reality it'll be anywhere from 150 to 250, depending on the type and size of 3 phase load. Make sure that any 240 volt single phase loads (like control transformers) are connected to X and Y. The only thing connected to Z is a 3 phase load.
Micromind:

I have a couple of questions on this setup... I don't deal much with phase converters but have installed lot's of 3 phase equipment.

If I follow you correctly, your saying use the single phase load from the panel to power the converter and also to supply 220, and 110 volt to X, Y, and W. Then your saying to get the 3rd phase/L3 only from the generator.

I have a couple of problems with that the least being that you would have 2 legs of 220 and a single 208 leg.

1. Is not the phase generator considered a power source separate from the main panel? If that is the case it would be a code violation to have supply voltages not comming from a single source.

2. Now, even if you had 110v from either X and Y to W. How is the OP suppose to guess how the controls are wired in that they could be pulling 110v off of Z and W. In that case you could have a disaster. You would have to know on which leg the panel is looking for 120v, X,w or Z,W. You have a 50-50 chance but that's bad odds.

Again, I'm no expert on phase converters but are'nt there any 5wire converters out there?

Last edited by kencaz; 05-09-2008 at 11:06 PM.
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Old 05-10-2008, 12:39 AM   #9
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3 Phase Converter Wiring


Notice in the drawing a few posts back how the single phase power goes to the converter, and 3 phase power comes out. What's not shown is that the single phase wires are spliced to two of the converter leads, and are also brought directly to the 3 phase load. Think of it like this; if you have an existing building service that is single phase, and you now need 3 phase, and the POCO has 3 phase outside, all they need to do is hang one or two more xfmrs on the pole, change the meter base, etc., and you have a 240 delta. You still have the same single phase system as before, but a third leg has been added to get 3 phase. A phase converter does the same thing. With either system, you have 240 across any 2 phases, 120 from 2 of the legs to neutral, and 208 from the 3rd leg to neutral.

As far as W, X, Y, and Z wiring is concerned, W, X, and Y are the exact same single phase as the service. Z is the added third phase. Article 455.9 specifically states that single phase loads downstream of the converter shall not be connected to the manufactured (generated) phase. Every phase converter I've ever connected came with explicit instructions and warnings to check equipment carefully to ensure that single phase loads are not connected to the generated phase. It's not all that hard to do, you really only need to avoid connecting anything thats not 3 phase to Z. If you remember what color you used for Z, it's easy.

Rob
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Old 05-10-2008, 08:21 PM   #10
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3 Phase Converter Wiring


Thank you both for the help and insight!
The converter (not generator. Duh) is a 10 HP CNC Rotary Converter.

Below is a modified version of the wiring according to micromind's info. It's all starting to make more sense...


Again, thank you!
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Old 05-10-2008, 09:55 PM   #11
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3 Phase Converter Wiring


Quote:
Originally Posted by ideffects View Post
Thank you both for the help and insight!
The converter (not generator. Duh) is a 10 HP CNC Rotary Converter.

Below is a modified version of the wiring according to micromind's info. It's all starting to make more sense...



Again, thank you!
Hmmm, I'd be surprised if that works... I would be curious to see what voltages your getting between L3 -- L2 since the input voltage from the panel L1 and L2 are unlikely to match the output L3 of the converter...

And if your even getting any voltage across L3 -- W?, which I would think not and could be a problem with the controls.

Good Luck and keep us informed...

KC

Last edited by kencaz; 05-10-2008 at 09:57 PM.
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Old 05-10-2008, 10:13 PM   #12
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3 Phase Converter Wiring


Thanks KC.

Let me ask you this. How would you do it safely so each line gets the correct power starting from single phase? Would there be something better to use than a phase converter that does not cost a fortune?

Also, since W (the common) is basically a ground, what would be the problem? The common should just complete the circuit, correct?
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Old 05-11-2008, 12:00 AM   #13
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3 Phase Converter Wiring


Quote:
Originally Posted by ideffects View Post
Thanks KC.

Let me ask you this. How would you do it safely so each line gets the correct power starting from single phase? Would there be something better to use than a phase converter that does not cost a fortune?

Also, since W (the common) is basically a ground, what would be the problem? The common should just complete the circuit, correct?
Well, I have been doing a little reading on the subject and it seems that most all phase converters generate a Delta 240/120 configuration. If that is the case then you may have a high leg situation where you have 240 between L1 and L2 and 120 between L1, L2 and Neutral, (W), however, the voltages between L3 and W would be 208V, and you would have a problem.

The best way to find this out is if you hook up the phase converter and measure the voltages.

It would be nice if you could give us some specs on what your attempting to run of of the converter. If the controls do require 120V and you can't separate them from the 3phase input then you may have to install and isolation transformer to convert the Delta configured output from the converter to a more equal WYE configuration. This would give you 208 across each leg and 120 from all three legs to neutral.

This is the only way I can see that you could do it without possibly re-wiring the controls...

Give us some info on what your installing...

KC
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Old 05-11-2008, 12:06 AM   #14
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3 Phase Converter Wiring


I can see two problems with the latest drawing.

The first one might not be an actual problem, it might be only a reference. W is shown grounded. If this is only a reference to the neutral being grounded at some point, (at the main panel), then it's OK. There can be only one neutral to ground jumper, is must be in the main panel or main disconnect, not the receptacle.

Secondly, 120 volts will exist from W to X, as shown, and it will also exist between W and Y, (which is not shown), but the voltage between W and Z will be anything but 120. Z can only be used for 3 phase loads, nothing single phase can be connected to it.

Other than that, it'll work as planned.

Rob
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Old 05-11-2008, 12:39 PM   #15
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3 Phase Converter Wiring


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Originally Posted by micromind View Post
Secondly, 120 volts will exist from W to X, as shown, and it will also exist between W and Y, (which is not shown), but the voltage between W and Z will be anything but 120. Z can only be used for 3 phase loads, nothing single phase can be connected to it.
This could be a major problem if your control was looking for 120v on W-Z. Again, you have a 50-50 chance.

I believe if he were to move L2 to Z and L3 to Y it could solve the issue since the control would not be looking for 120v accross W and Y.

KC

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