# Can you use a 3 phase on/off switch with single phase power?



## gearhead

Details: I bought a Powermatic 6" belt sander that had a 3 phase motor. The seller gave me a single phase motor to swap into it. I made the swap and want to use the original on/off dual-button power switch. Now, when I push the ON button and hold it in the motor starts, but the switch will not remain engaged. The minute I take pressure off the button the power goes off. I have looked at the switch innards and don't understand how it works. Does it maintain contact in 3 phase operation with some kind of electromagnetic function? It's obviously different than a regular toggle type of switch. To be clear, I am not running the single phase motor through any of the other 3 phase electrics. The single phase motor just plugs into the wall and I wanted to use the existing power switch if I can. If not, well, I'll just swap it out. I've been doing some internet searching and can't find further info. Thanks.


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## Tony Wells

I wouldn't do that too much. Those contacts are probably not rated for the voltage and current of the motor. I would say there is a magnetic contactor involved, and the push button station is rated only for the coil voltage and current for it. But yes, the answer is you can do this with the existing  electrics. If possible, can you post a photo of the control box? I can give you a diagram to follow if I can see what contactor is there.


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## gearhead

Thanks, Tony! No, I didn't goof with it too much, just went, "Huh, well that's not going to work," and left it at that. I don't even have a sanding belt on it yet.

At any rate, I believe this is the control box you wanted a photo of:


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## Rbeckett

GH,
Looks like you got the man on it already.  Tony definately know his stuff about 'lectricity so tou can depend that what he says is dead nutz good info.  Follow his advice closely and you will have very few problems.  I trust Tony to wire anything in my house or shop that needs it.
Bob


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## gearhead

Rbeckett said:


> GH,
> Looks like you got the man on it already.  Tony definately know his stuff about 'lectricity so tou can depend that what he says is dead nutz good info.
> Bob



Excellent, excellent. Good to know. I hope that this is the last of the screwing around I have to do with this thing. Between getting this thing lugged down my tiny stairs into the basement and installing the single phase motor, I've about had my fill of things. Still have a Powermatic band saw that has to go down there too. At least that one is already single phase. Too bad I can't get people to help lift things over the internet, or I'd have that thing installed already.


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## Tony Wells

Well, I just got in from a rather large meal celebrating my wedding anniversary, and I feel a strong need for a nap. When I get back up, I'll go over how the existing system works, and an easy way to incorporate it into a 110 volt two button stop/start system. If I tried to explain it now, I'm sure it wouldn't make much sense. Ah'll be Bach!


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## gearhead

Congratulations on the anniversary, Tony. I'll be happy to wait until you're making sense(!). I like that the word "easy" was included in the coming instructions!


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## Tony Wells

Thanks, Gearhead!

Now to your situation. Before we get too specific with Furnas, let's look at this. This is specifically for using a 3 phase starter on a single phase motor. 






And forgive me if I either spell out too many elementary details, or omit too many. usually I get into too many irrelevant details, or add too much information not truly germane to the discussion. After you look at this, we'll talk about the specifics of your installation. We do need to know what the coil voltage in the contactor. If there is a control transformer in the enclosure, we need the specifications on it.


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## Hawkeye

Gearhead,

From your description of the operation, you're almost there. If you refer to Tony's diagram, you'll note the two parallel lines to the left of the circle in the "Contactor Relay" section. The circle represents the coil that pulls in the contacts. The small parallel lines to the left represent the holding-in contacts connected in parallel with the "on" pushbutton. These contacts are not doing their job. When they are closed, they are doing the same job as the pushbutton and hold the contactor in.

Make sure power is disconnected. Check the wires running from the coil terminalsto other parts of the circuit. You should be able to trace wires to all of the points related to the start and stop buttons, including a set of lighter terminals on the upper (green) contactor. If anything appears to be missing, trace it through logically and see what is needed to make it work. Check especially to see if it is trying to pick up power from the set of large contacts that is no longer being used. Remove the wires that aren't going to the motor any more.


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## gearhead

It seems I'm still pretty far off, Hawkeye. I do not have the power running through any of the current 3 phase electrics. The single phase motor has two cords coming out of it, one for power supply that has a wall plug, the other for the switch. I wired the switch wires directly to the 3 phase push buttons, and that's where I'm at right now. I need some time to get back down in the basement, but it looks like I need to be running power through the Furnas and then into the motor, correct?


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## Wade8A

GH, what is the HP of your single phase replacement motor?  Your NEMA size 00 starter is only rated for up to 1 HP on 240V.  Assuming you are ok there, you may have to install different heater coils to match the full load amp rating of your motor.  The E48 coils on your starter are rated for 5.62 to 5.91 FLA.  http://www.southlandelectrical.com/FurnasHeaterChart.asp  If you need new heaters, Southland Electric can provide them for you.

Greg


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## Hawkeye

GH, you are correct in that the power should go through the controls and not directly to the motor. Study the connection diagram on the motor and remove all of the wiring coming out of the junction box. Connect a pair of wires, plus ground, in the configuration that works for your intended voltage and direction of rotation. Connect those wires to the output of the contactor. All other wiring relates to running the power into the contactor and the control circuits, which should match the diagram Tony posted.

Wade8A, thanks for the link. I'm setting up a Furnas size 0 to control the new single-phase motor in my 'new' mill. Your link tells me I need E61 heaters for my 16 amp motor.


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## lotechman

Thanks to this post I got brave and my mag switch now works on single phase.  I am not concerned about the heater section since my VFD provides motor protection.


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