# Reversing a single phase 120 V motor



## Jimbir (Feb 15, 2019)

First, thanks for letting me join this group.
I have an old Delco motor with four leads, two of them are line in and the other two are red and connected to terminals on the motor. The nameplate on the motor says "to change the rotation Reverse the two red wires". I'd like to control this motor with a double pole double throw center off switch. Can someone send me a diagram showing how to wire this combination?

Thanks, Jim Birke


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## markba633csi (Feb 15, 2019)

Hi Jim, 
A toggle switch would connect like this,  jumper wires needed between 2,5 and 1,6
You may need a second switch to turn the motor on and off


Mark


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## Jimbir (Feb 15, 2019)

Yes. Just a simple three position toggle switch.

Jim


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## Jimbir (Feb 15, 2019)

markba633csi said:


> Hi Jim,
> A toggle switch would connect like this,  jumper wires needed between 2,5 and 1,6
> You may need a second switch to turn the motor on and off
> View attachment 287819
> ...


Where would the line in wires be connected?


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## markba633csi (Feb 15, 2019)

Line in wires as per your photo, left side posts
Also you should be using a 3-wire power cord, 3rd ground wire connects to a motor housing screw
M
ps you need to extend the red wires as long as necessary to reach the toggle. Same with the posts connections.
If the motor does not stop with switch in center position you will need a second switch to remove power to the motor


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## markba633csi (Feb 15, 2019)

If that is an instant-reversing motor you need to use caution, if this is for a lathe (chuck can loosen when spun in reverse)
Mark


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## David S (Feb 15, 2019)

I would recommend a separate ON / OFF switch, rather than a single three position centre off switch.  Just incase when turning it off quickly you didn't go into reverse.

Also a good point about chuck attachment.  I know my Atlas 618 will spin the chuck off If I am not careful.

David


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## Jimbir (Feb 15, 2019)

Since you don't use reverse very often, I'm thinking (not my strong suit) a spring-loaded tab that would prevent you from switching into reverse until you lifted it. Along the lines of the hooded prop feather switches on an airplane.


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## hman (Feb 16, 2019)

Or something like this?  Got this switch cover from Radio Shack, before they went belly up.  I'm pretty sure you can still get them from electronics suppliers.  Grainger has them for $6.34:





						Toggle Switch Cover, Switch Collar Mount
					

Toggle Switch Cover, Switch Collar Mount




					www.grainger.com


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## KBeitz (Mar 10, 2019)

Use a 3 pole double throw toggle switch.


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## Truefire (Mar 14, 2019)

Just make certain that the switch comes with a cover like 'Hman' posted (in post #9) or that you make some sort of cover so that you do not (and can NOT) accidentally bump the switch in the opposite direction while motor is in operation.  I'm certain you know this but it's worth saying, make certain toggle sits in center position until motor has come to a complete stop.  I accidentally fried my board on a piece of equipment because I didn't have a cover, brushed the switch and inadverntently flipped it.  It created an emotional event   $$


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## Superburban (Mar 14, 2019)

Those covers are made to keep the switch in off, on a two throw (on/off), or one of the ends in a 3 throw switch(on/off/on).  I have never seen on that will lockout one throw of a 3 throw switch. 

You can easily make a block, using a spring loaded hinge, with one side cut, and bent so that it will block the one end movement.\, and needs to be pulled out of the way to use that position of the switch.


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## Truefire (Mar 14, 2019)

Superburban, well there are tons of them out there, without covers, that's why I posted what I did.


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## Bi11Hudson (Mar 14, 2019)

Old geezer throwing his 2 cents worth in, yet again. This issue has been covered many times in the past, just look into older posts. It seems to have been covered here, as well. Although a little spotty, with so many contributors holding forth. I am (was) a commercial/industrial electrician. This job is always just a few minutes of studying the motor and then hooking it up. You've already studied the motor, so... ... ...
    First issue, single phase motors are *NEVER* instantly reversing. Plugging only works on 3 phase and DC motors. If you flip the reversing switch when it's running, nothing happens. It keeps running, usually to the detriment of whatever work is being done. There must be an *ON/OFF* switch, usually separate. There are exceptions to these, as any, rules. But, all in all, rare.
    Many(most) folks *end up* with a drum switch, which serves both purposes. Although they may not have started with one. Looking into the "innards" of a drum switch, you will find a pair of contacts that operate in both directions. And four others that make up a reversing switch. I won't go any further on that subject because there are many different designs.
    To answer your original question, you will need 2 switches. Assuming that most of your work will be uni-directional, the ON/OFF switch is the more subject to wear. On my Atlas miller for example, I had the front panel switch  for ON/OFF. The reversing switch was hanging on a pigtail that dropped from the motor. It was eventually rewired with a drum switch, once I settled on a standard. In your case, where to hang the switch will be your call. Just make it a determined movement to operate.
    There are several switches that are for that purpose, mostly costly. Just a DPDT switch works well enough. Wire the two red wires to the center two lugs. Wire the two motor stabs to the two lugs on one end. Then take the other two lugs and cross them and connect to the first end. Most any switch will do the job. Just look for the six lugs on the back. Go for the higher current switch, if available. The post prior has a very good photo of the switchs. The one on the left.
    I must apologize, I'm still recovering from a computer crash. I have the drawing, just not sure where it resides right now. A couple of months back, I was prowling on eBay. There was a listing for a motor switch, a drum switch, for about $12US. Plastic, but well made. No flexing. I bought a half dozen, some to "standardize" my machines, some for standby parts. Not much more than a good toggle switch will cost. Just a longer delivery time. Worth looking for... ... ... BTW, WinDoze 10 sux, big time... ... ...
Bill Hudson​


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## Superburban (Mar 14, 2019)

Bi11Hudson said:


> First issue, single phase motors are *NEVER* instantly reversing. Plugging only works on 3 phase and DC motors. If you flip the reversing switch when it's running, nothing happens. It keeps running, usually to the detriment of whatever work is being done. There must be an *ON/OFF* switch, usually separate. There are exceptions to these, as any, rules. But, all in all, rare.
> 
> Bill Hudson​


Thankyou Bill. I thought that was the case, but not positive. Now I know. Will it hurt the single phase motor? my understanding is the run windings are the same for either direction, it is the start windings that work differently for each direction. So fliping the switch while the motor is above the speed where the start winding switch kicks out, will do nothing.


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## Bi11Hudson (Mar 14, 2019)

Operating the reversing switch while the motor is running, in most cases, will do nothing because the "start winding" is run through a centrifugal switch that opens at around 50% speed. But will cause a definatly  unsettling experience the next time power is cycled. Basically the motor runs on one winding once up to speed. There are exceptions, sure. But the way you described the motor, it sounds like the theory fits. 
    It won't damage the motor in most cases, unless something out of the ordinary happens. Like when it doesn't start "right now", the magic smoke will get out. As long as it comes up to speed in a second or two, you're good to go. When you question whether or not there is something wrong with the motor, remove the load(belt) and run it. If it runs well enough there, then start looking. If it hums, or rattles, or shakes, and doesn't come up to speed right away, look at the *capacitor first*. *Then* the start switch. The cap is easier to get to, and the most likely to fail. Keep an extra on hand and swap it out at the first sign of trouble. The centrifugal switch is inside, and very difficult to get back together right.


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## Truefire (Mar 15, 2019)

Hudson, thank you for highlighting that a motor's centrifugal switch is out of operation when a motor is at full speed.

For others that follow, a motor's internal centrifugal starting switch, does become engaged again (drop back in) when the motor begins to slow down.  This does occur with most motors while motor shaft is still spinning from it's prior operation.  With some motors that's almost at creep revolution.  But, none-the-less, the centrifugal switch does drop back in and become 'engaged' again while motor's rotor (shaft) is still in motion.  You can hear the switch on most motors if you listen closely.....sounds like a clicking sound coupled with a thud.

For what it's worth and for clarity sake on my part...of the switches that I posted in #13, the two on the right are more than likely not rated for the amperage capacity of most motors on most of our machines.  Some smaller benchtop machines, using small dc motors, they may be fine.  I had posted those three photos, by just arbitrarily grabbing some offline, as a measure to reveal there are double pole, double throw switches which don't possess safety covers.  I didn't however, consider them being interpreted as a suggestion of a grade of switch to be used in this situation.  That is my fault, I should've put more thought into my post I suppose.   

However, as Hudson highlighted, the one of the left could more than likely be used for a situation similar to the original post.  It has beefier contacts and spades, which appear to be of a rating to handle a 1/2-3/4 horse single phase motor.  Most of that particular style are rated upwards of 15-20 amps.

I apologize for taking the thread into skewfield for a moment.  

(changing gears) The start windings are no different than run windings in the way they see electricity.  Apart from the fact, which we will not get into, their make/turns and wire size are different for the start winding.  But they don't "work differently than run windings".  They're just a winding just as the running winding is.  It's just that when we switch the hot and nuetral wires 'ahead of' the start capacitor, which is what we are doing with the double pole-double throw switch, that we reverse the path of the power feeding through -capacitor to start winding- so that it's now flowing through -start winding to capacitor-.  And its that momentary current lead or lag associated with this arrangement which allows either the start winding or run winding to build up it's magnetic field before the other.


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## Bi11Hudson (Mar 15, 2019)

I'm not sure where it came from, but a response showed up in my eMail inbox. Maybe I'm just not up to speed yet on this new WinDoze 10 stuff. When I answered, it bounced.
    The biggest reason I pointed out the switch from the post was that it indicated the crossed wires clearly for a reversing switch. I have used that contact arrangement for many a year with my model trains. Going back to the 60's... ...
    Once I came off of ships in the early 70's and went to work in the mills, it was instinctive. The drum switch I mentioned is at:
https://www.ebay.com/itm/60-A-Drum-...877932?hash=item5b5075232c:g:UxwAAOSwfQtbUAmo
The price hasn't changed much, a few cents higher. They include a diagram in their posting. But it shows only which terminal to connect to, not what the contacts actually do.
    I am pleased with the heavy plastic used. Not flexible in the slightest. At 60 Amps, it should stand up for a long time on fractional HP motors like I use.
    BTW, my Atlas mill must be reversed because in addition to the arbor mounted cutters, I use single ended end mills. Reversing the motor  prevents "climb" milling that way.

Bill Hudson


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## Blackjackjacques (Apr 11, 2019)

As a matter of isolation, you never want to break out 120V lines to a switch appliance, especially a metal bat handle type switch.  I see it done all the time, and although expedient, it is not cool.  The preferred means is using a relay with the switch powering a low voltage relay coil.


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## Truefire (Apr 11, 2019)

Blackjackjacques said:


> As a matter of isolation, you never want to break out 120V lines to a switch appliance, especially a metal bat handle type switch.  I see it done all the time, and although expedient, it is not cool.  The preferred means is using a relay with the switch powering a low voltage relay coil.


Just to clear up the waters for any future readers-- it's perfectly ok to use 120 volts at drum switches.  I wouldn't say "never".  There are more than one ways to wire up projects and some ways could be argued to be safer than others.  However, modern drum switches are almost always rated up to 600VAC and possess contacts which are not only engineered to carry motor loads but manufactured to do so.  As far as concerns regarding shock hazards, this is what the green bonding screws are for inside the device-- for grounding the metallic housing to prevent electric shocks.


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## Superburban (Apr 11, 2019)

Agreed. Look around the house, and shop. Very few 120V items use relays. almost all have the 120V right behind the switch. Electronic items are the main things I see looking around, taht do not, and they are likely done more for noise isolation, and simplicity in manufacturing, then to move the 120V away from the switch.


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## Truefire (Jun 28, 2019)

Superburban said:


> Agreed. Look around the house, and shop. Very few 120V items use relays. almost all have the 120V right behind the switch. Electronic items are the main things I see looking around, taht do not, and they are likely done more for noise isolation, and simplicity in manufacturing, then to move the 120V away from the switch.



Agreed-- I think it is more often than not--simply done for economics there within the manufacturing process.  Saving that green.  That and the electrical noise issue.  

When looking at it from a global perspective, where the vast majority of the electrical component manufacturers are located, our 120V is already seen as a low voltage.  On the other side of the pond anyway.   Almost 80% of the world utilizes 230 volts for their common, everyday lighting and general purpose receptacles..even within their little huts.  We're the only ones really using 120 volts.


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## ErichKeane (Jun 28, 2019)

FWIW, I have used this drum switch before and really liked it: https://www.ebay.com/itm/Drum-Switc...fIAAOSwsZJaYFmX:sc:USPSFirstClass!97119!US!-1

It has a center 'off', can switch 2 wires at once, and has a pretty solid on/off to it.  I wired an E-Stop button in when I put it on my lathe, but it works really well for this use case.


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## Truefire (Jun 28, 2019)

Erich, do you have a three phase motor in your arrangement or did you just break your start winding's leads across contacts 2,3 and your nuetral across 1 for a single phase arrangement?  Those are nice switches by the way...made fairly decent.


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## ErichKeane (Jun 28, 2019)

Truefire said:


> Erich, do you have a three phase motor in your arrangement or did you just break your start winding's leads across contacts 2,3 and your nuetral across 1 for a single phase arrangement?  Those are nice switches by the way...made fairly decent.


I'd only had a single phase motor with that drum switch.  Typically the 'reverse these two wires to reverse rotation' for single phase is how it works, so you just wire up the motor like normal, then have the two reverse-wires go through the two diagonal parts of that switch.

I wired the ground directly to the motor.  I wired the lines to the unchanged wires directly.  Then, I pulled the "red" wires (the ones needing switching) into the switch on 1 side, and the two line-ins into this switch as well.


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## ErichKeane (Jun 28, 2019)

Here is how I wired mine.  The motor side was slightly more complicated (additional wires/stuff since it was a dual voltage motor).  I chose blue for Line in, since white shows up poorly   There is also a ground that just goes 1 to the other.


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## Truefire (Jun 28, 2019)

I'm familiar with wiring, I had initially asked because we have a lot of outside readers that land on this forum and therefore desire some clarity.  I knew you had a slightly unique situation, in that, it's not as simple as switching the two leads supplying the motor.  After your pictorial, indeed you do. Essentially what someone did- either you, the manufacture or someone owning the setup before you, had the start winding leads extracted from inside the motor housing and pulled outside of it...this is not the case for most single phase motors.  Others would have to dig those wires out from underneath the end cap and extend them to create a situation like yours.  In your scenario, after that was obviously done, then that switch works great--we were just flipping the start winding leads.


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