how do you rewire a 1952 Delta Unisaw Rockwell Milwaukee table saw from 230 (220) to 115 (110)?

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Forum topic by bbbben posted 12-27-2014 02:46 PM 10219 views 0 times favorited 36 replies Add to Favorites Watch
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5 posts in 1425 days

12-27-2014 02:46 PM

Topic tags/keywords: rewire low voltage high voltage delta table saw vintage rockwell milwaukee question tablesaw

I would like to rewire the Delta table saw I just got from my grandfather from 220 to 110. I opened up the side of the motor and was surprised to find that the wires from the motor are numbered 1, 2, 3, and 4 … not colored (as the diagram on the motor indicates)!

Does anyone know how I should rewire this motor for 110?

Currently it is wired as follows (for 220):
1 to white
2 to 3
4 to black
green on screw to green on 220 plug

I bet it should be as follows for 110, but I want to make sure:
1 & 2 to white
3 & 4 to black
green on screw to green on 110 plug

Here is a photo of the diagram on the motor:

Here is a photo of the table saw:

Delta Rockwell Milwaukee table saw
CAT = MK-85B010
H.P. = 1
R.P.M. = 1725
Type = SR
Volts = 115/230
Amp. = 11.8/5.9
I based the year (1952) off the serial number

Thank you so much for any help you can provide!!!

36 replies so far

View Tennessee's profile


2891 posts in 2692 days

#1 posted 12-27-2014 03:16 PM

You are probably correct, but this is probably a motor with a start winding and a run winding and at 230 VAC they might have wired the start winding out of the picture. But I am guessing.

What I think did happen is the motor got rewound somewhere along the line, and the rewind shop put in the standard wire numbers and used all one color lead wire, which would be typical for a rewind shop.

-- Tsunami Guitars and Custom Woodworking, Cleveland, TN

View bbbben's profile


5 posts in 1425 days

#2 posted 12-27-2014 07:58 PM

Thank you for your input, Tennessee.

View Dallas's profile


3599 posts in 2665 days

#3 posted 12-27-2014 08:04 PM

Pull it out, take it down to your local electric motor shop and let them rewire it.
I would spend the extra money and have them go through and replace everything that needed it and let you know what condition the motor is in.

-- Improvise.... Adapt...... Overcome!

View dhazelton's profile


2789 posts in 2474 days

#4 posted 12-27-2014 08:27 PM

You’d actually be better off spending that same money to put in a 220 outlet. The saw will thank you.

View bbbben's profile


5 posts in 1425 days

#5 posted 12-27-2014 08:50 PM

More good input, thanks. I have decided not to put in a 220 plug because it would cost too much to run 220 to my detached car port… there’s already 110 out there…and I’m not worried about the cost of drawing twice as many amps with it not being used daily.

View johnstoneb's profile


3037 posts in 2350 days

#6 posted 12-27-2014 08:57 PM

220 and 110 draw the same amps. With 220 the load is split half the amps go down one leg and half down the other leg. You’ll get more torque and a quicker startup with the 220. It may run cooler on 220 also.
I would do as Dallas suggests. That is a 60year old motor probably still good but needing serviced. That would be a lot cheaper than replacing the motor because it needed a service and din’t get it.

-- Bruce, Boise, ID

View Dallas's profile


3599 posts in 2665 days

#7 posted 12-27-2014 09:14 PM

Bruce, Not actually true.

120V draws twice as many amps as 240V because everything comes down to power consumed, This is expressed in watts.
The formula for determining watts is V x A = P (P is expressed as watts).
In a perfect world without friction or other losses, 1 HP equal 746 watts. Real life makes it about 800 watts.

Therefore, using the 800 watt figure, 800w / 240v = 3.333a.
With 800w / 120v = 6.66a

HP, and watts always stay the same. Any change in voltage or current draw will effect the wattage number.

-- Improvise.... Adapt...... Overcome!

View CypressAndPine's profile


62 posts in 1985 days

#8 posted 12-27-2014 10:35 PM

Dallas is correct. 120V will draw twice the amps.

You are correct
1&2 to white
3&4 to black. Run it like this without WITHOUT A BLADE and check that rotation is correct.

If the motor spins the wrong way wire it as follows:

1&3 to white
2&4 to black

Be sure your earth cable (green) is grounded properly to the motor frame or machine frame. Also remember to test it without the blade to be extra safe. Have plug in hand in case there is a short circuit so you can unplug it quickly. It should work, but be safe because it looks like an old motor.

I am an industrial electrician so I hope you can trust me.


-- Cypress Jake, New Orleans

View chrisstef's profile


17721 posts in 3184 days

#9 posted 12-27-2014 11:00 PM

Great score on a bullet motor uni. Shes a keepah!

-- Its not a crack, its a casting imperfection.

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18381 posts in 3854 days

#10 posted 12-28-2014 12:58 AM

I’m going to disagree. 1 & 2 are probably the ends of winding #1. 3 & 4 are probably the ends of winding #2.

1&3 to white and 2&4 to black should work for 120 volts. If it hums or blows your breaker, the winding are opposing one another. Reversing the wires will not reverse the rotation of this motor.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View REO's profile


929 posts in 2252 days

#11 posted 12-28-2014 04:23 AM

it is easy to check with an ohm meter to find which are opposing ends of the windings. For low voltage the windings are in paralell for high voltage the windings are in series. for those who say that there is a different draw current remains constant. Amps x volts = watts (power) therefore 110 volts 11.8 amps 1298 watts (low voltage). 220 volts 5.9 amps 1298 watts high voltage. The noticeable start up difference and a lower power on low voltage can usually be attributed to the connection wire size and voltage drop. if you want to run heavy gauge wire to the saw it will start just as fast and generate the same power. The power remains constant and heat generation is the same because the windings actually carry the same current in both configurations.
Just an experiment: plug a circular saw directly into an outlet and pull the trigger. The plug the saw into a 100 foot cord and the cord into the outlet and pull the trigger. There will be a noticeable difference even with a heavy gage cord.

View bbbben's profile


5 posts in 1425 days

#12 posted 12-28-2014 04:33 AM

Thanks again, everyone, for responding! Every bit of input is appreciated.

Reo, do you mind going into more detail as to how I would use an ohm meter (voltage meter?) to make sure I wire it correctly for low voltage? (I am grateful for your patience explaining things that are most likely very elementary!)

View REO's profile


929 posts in 2252 days

#13 posted 12-28-2014 04:20 PM

if you have a reading or continuity between two leads they have to be a continuous winding. if there is no reading then they are different windings.

Make sure all the leads are separate. put your meter or tester on 1 and 2. if they are both ends of the same winding then your meter will light beep or display a reading other than 0 or OL.
it could be 1-2 (A) 3-4 (B) or it could be 1-3 (A) 2-4 (B) you cant tell for sure without testing
if you GET a reading on 1-2
1-3-white 2-4-black
if you DONT GET a reading on 1-2
1-2-white 3-4-black
white and black from the cord can be switched around and make no difference.
switch off. plug in the saw without the blade and quickly switch the saw on and off again checking for movement and rotation. in a four wire dual voltage motor it is possible to reverse rotation by changing two leads.
check this far and get back if the direction is wrong or it just hums or buzzes.

View Dallas's profile


3599 posts in 2665 days

#14 posted 12-28-2014 08:51 PM

Reo, I disagree about your figure of 1298 watts per HP, except under certain unusual conditions. It’s nearly as far off as my 746 watts. I have history and math on my side, along with the ratings on the motor pictured above.
Curiosity leads me to ask where the 1298 watt figure comes from.
I’m seriously not trying to start an argument, but I have never heard that figure before. I would like to find out the reasoning behind it.

Most of the time, I figure 1Kw per HP, it makes life easier.

Horsepower and watts are both units of power, just from different systems of measurement. One horsepower (interestingly the horsepower was defined by James Watt) is 33000 lbf x ft/min (lbf = pound force). One watt (of course named after James Watt) is defined as 1 N x m/s (N=newton). To convert simply convert each underlying unit:

33000 lbf x ft/min x (1 min / 60 s) x (4.448 N / 1 lbf) x (1 m / 3.28 ft) = 745.85 N x m/s = 745.85 W

It doesn’t matter what type of power we are talking about, the conversion between HP and W is fixed.

The difficulty when dealing with electric motors is (1) motors are rated by the number of HP they deliver (under very specific conditions) and (2) we are generally concerned with the current which they draw. The 745.85 W/HP conversion factor would only apply for a perfect (100% efficient) motor which presents a purely resistive load. A real motor will have less than 100% efficiency (consuming more power than is delivered to the load) and will present a reactive load (meaning that the current draw is higher than the number of watts consumed would indicate).

-- Improvise.... Adapt...... Overcome!

View klassenl's profile


190 posts in 2837 days

#15 posted 12-29-2014 12:50 AM

Reo, I disagree about your figure of 1298 watts per HP, except under certain unusual conditions. It s nearly as far off as my 746 watts.
- Dallas

All Reo did here was apply Ohm’s law (in one of it’s forms) Watts = Volts * Amps. There is where 1298 comes from.

-- When questioned about using glue on a garbage bin I responded, "Wood working is about good technique and lots of glue........I have the glue part down."

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