# Phase Converter



## sparky80 (Aug 1, 2016)

Hi guys I went to look at a job this afternoon in a woodworking shop. He had purchased a used phase converter. I have wired all in one units before, but this one was made by Desco Electric and had a capacitor bank in a control/splice box and a separate 30 horsepower motor. Any advice on a wiring diagram and the best way to make a code compliant installation? Thanks in advance.


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## Tonedeaf (Nov 26, 2012)

does it have just 3 wires?


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## MechanicalDVR (Dec 29, 2007)

Model and maybe serial number would help.


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## sparky80 (Aug 1, 2016)

The control box has a L1 and L2 for the single phase and L1, L2, and L3 for the outgoing. Hope that answers your question.Thanks


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## Tonedeaf (Nov 26, 2012)

alot of times the wires aren't marked

two of the wires do the magnetic controls. trace them out they are L1 and L2 single phase.

Run L1 and L2 through a 3 phase fused switch to the converter motor and load.

Run the 3rd wire from the converter motor through the last leg of the fused switch to the load.


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## sparky80 (Aug 1, 2016)

I didn't see a model or serial number for the control box. Sorry.


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## sparky80 (Aug 1, 2016)

What wire size would you recommend? He is currently feeding a 3 phase panel with two smaller units in parallel. It is a rather "rough" looking set up.


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## Tonedeaf (Nov 26, 2012)

80amps #4 awg copper...the phase converter needs to be rated to for 30HP


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## hardworkingstiff (Jan 22, 2007)

A quick Internet search pulled up this.


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## sparky80 (Aug 1, 2016)

Thank you for the replies. Very helpful. Someone has bundled the wires on the motor and labeled them A, B, C. L1 and L2 to A&C then the third phase from B?


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## hardworkingstiff (Jan 22, 2007)

sparky80 said:


> Thank you for the replies. Very helpful. Someone has bundled the wires on the motor and labeled them A, B, C. L1 and L2 to A&C then the third phase from B?


If this is not factory labeling, I don't know that you can make a correct assumption (you might get lucky, you might not).

Any way to use an ohmmeter to determine which 2 leads actually drive the motor on the phase converter?


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## hardworkingstiff (Jan 22, 2007)

Since L1 and L2 feed the load and the RC, it is safe to assume that L1 and L2 remain 180 out (in reference to neutral) and the manufactured phase is 90 degrees out from L1 and L2?


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## sparky80 (Aug 1, 2016)

I took some pictures and just reviewed them. The control box is AB on L1 and L2. And is labeled ABC on the outgoing side so, I think the ABC listed on the motor has the third phase as C. Hope that makes sense.


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## JRaef (Mar 23, 2009)

sparky80 said:


> I took some pictures and just reviewed them. The control box is AB on L1 and L2. And is labeled ABC on the outgoing side so, I think the ABC listed on the motor has the third phase as C. Hope that makes sense.


It doesn't really matter, but what IS important is that you know and mark all of the 3 phases so that you always know which two are "real" and which one is "manufactured". The reason is, you don't want the manufactured leg going to anything other than true 3 phase loads like motors or heaters. So a common issue is control power transformers and single phase power supplies. You ALWAYS want those fed from the real phases. So when you hook up a machine that was originally made for 3 phase, you want to go through the control panels and ensure that all tap offs are connected to A and B in your case. That's likely WHY yours is wired this way now, because the machine was already tapping control power from A and B, so connecting the RPC that way saved them the trouble of rewiring the controls.


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## mitch65 (Mar 26, 2015)

Make sure that the machine connected to the phase converter is interlocked so that it cannot be started without the converter running. Saw a MAU motor burn up last summer because somebody started the MAU without running the converter and single phased the motor to death.


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## JRaef (Mar 23, 2009)

mitch65 said:


> Make sure that the machine connected to the phase converter is interlocked so that it cannot be started without the converter running. Saw a MAU motor burn up last summer because somebody started the MAU without running the converter and single phased the motor to death.


Seems intuitive, but yes. I've seen similar mistakes.


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