Odd plug on table saw - Woodworking Talk - Woodworkers Forum
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post #1 of 80 Old 08-07-2016, 08:51 PM Thread Starter
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Odd plug on table saw

Last week I was given an old 10 inch craftsman table saw. One of the old heavy duty jobs. However, when I was checking it out this afternoon, I noticed the odd electrical plug. It appears to be a NEMA 6-15 or 6-30. It has the standard ground prong but the blades (which are the same size as the regular 120 15 amp blades, are turned the perpendicular to the regular 120 15 amp plug blades. (The closest I ever got to working with "phases" is being a stargazer and watching the moon. )

My work shop is not equipped for anything but simple 120, I suppose I could run a 240 volt line, but what a hassle
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post #2 of 80 Old 08-07-2016, 09:13 PM
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I think you know the options, if the motor nameplate says 120/240 and has a wiring diagram you can swap the wires around and run it 120. If not, it's run a 240 circuit or get a new motor. Or, just to include all the options, install a 120 to 240 transformer, which would be unusual.
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post #3 of 80 Old 08-07-2016, 09:39 PM
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The saw is wired for single phase 220. Rather than trying to re-wire the saw to 120v it will preform better on 220v so I would run a wire for it. Run at least a 12ga wire. If you have to go far from the breaker box I would go with 10ga.
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post #4 of 80 Old 08-07-2016, 09:53 PM
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Originally Posted by Steve Neul View Post
The saw is wired for single phase 220. Rather than trying to re-wire the saw to 120v it will preform better on 220v so I would run a wire for it. Run at least a 12ga wire. If you have to go far from the breaker box I would go with 10ga.
You are never going to get it are you Steve...

OP, check the motor plate, insure you have a single or "1" phase motor. Look for a marking that also indicates 120/240v or something similar. There is a high probability this is what you have but you need to check to make sure. Then you will need to pull the plate on the motor and check to see if it's wired for 120V or 240V, the plug won't tell you that. Someone could have had a special setup they used that plug for, just because it is a 240V plug, doesn't mean it's wired that way, so check.

If it is 120V, then install a new plug and you are golden. If it's wired for 240V then you need to decide if you want to run a 240V circuit, or if you have a sufficiently sized 120V circuit to run the saw.

The saw will not run better on 240V, so there is no need to waste your money on a 240V circuit, unless you want one in the shop.
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post #5 of 80 Old 08-07-2016, 10:08 PM Thread Starter
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Thanks every one. My knowledge of electricity and circuits is vry elementary, but I am learning.

The manual indicates that the thing was originally 110 volt, and cautions against changing the voltage up, even though some of the OEm motors were either 110 or 220. Saw I guess it is back to the barn to see what motor is on it. My only attempt at rewiring a motor thus far has been abysmal. No motter how I wire it it runs the wrong way. So I just used the old lathe by reversing the tool rest and letting it run backwards. Got three better lathes since so that lathe will be just given away.
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post #6 of 80 Old 08-07-2016, 10:18 PM
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I am with Steve on this, sounds like it is wired for 220 and if you can run a new 220 circuit do it, never regretted running 220, can't say the same for 110.

Never could understand why a motor would be dual voltage when there was no advantage to running it on 220 instead of just plugging it into a common 110 outlet.

Wise men speak because they have something to say; fools because they have to say something -Plato

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post #7 of 80 Old 08-07-2016, 11:46 PM
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I am with Steve on this, sounds like it is wired for 220 and if you can run a new 220 circuit do it, never regretted running 220, can't say the same for 110.

Never could understand why a motor would be dual voltage when there was no advantage to running it on 220 instead of just plugging it into a common 110 outlet.
The answer is, in terms of wiring costs, it can cost less to run a 240v circuit than a 120v circuit. And, it is true that you are more likely to have voltage drop when you plug a saw wired for 120v into a 120v circuit than a saw wired for 220 into a 220v circuit.

It is also true that if the wires are sized and run correctly a 120v circuit is as good as a 240v circuit, it's all in the voltage drop. That's because a 120/240 dual voltage motor winding always runs at 120 volts, it's why you have to swap the wires around. If you run 240 into a dual voltage motor without rewiring it to reduce the voltage at the winding's to 120v it burns up in seconds.

This gets covered over and over again, so lets look at it from a practical view. If the OP has a garage someone ran a 120v lighting circuit to, and it's a long run, and maybe there is a freezer plugged into it and 300 watts of light bulbs, there will be problems running a table saw on it. So, a dedicated 240v line is run to it, resulting in a vast improvement to the saw. Is 240v better than 120v? No, but in so many real-world cases, for practical reasons a 240v circuit has solved a lot of problems.
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post #8 of 80 Old 08-08-2016, 12:25 AM
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And I have said this before here that I have a 2 HP air compressor that has been fitted with a 1.5 HP motor because it's all I had at the time (35 years ago but it's still running). If I run it on 120V then I have to let air out of the tank for it to run but when it is wired 240V it starts as soon as the switch calls for it to run. When I had my old DeWALT radial arm saw on 120V it took longer for the blade to come up to speed than when I wired it for 240V, so I'm sold on 240V is better. Everything in my shop that can run on the higher voltage is running 240V.
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post #9 of 80 Old 08-08-2016, 01:42 AM
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And I have said this before here that I have a 2 HP air compressor that has been fitted with a 1.5 HP motor because it's all I had at the time (35 years ago but it's still running). If I run it on 120V then I have to let air out of the tank for it to run but when it is wired 240V it starts as soon as the switch calls for it to run. When I had my old DeWALT radial arm saw on 120V it took longer for the blade to come up to speed than when I wired it for 240V, so I'm sold on 240V is better. Everything in my shop that can run on the higher voltage is running 240V.
If you drag that compressor over to the panel and run a 120v circuit to it with #12 wire it would probably run better than it does now with 240v. Clearly there is a voltage drop issue with the 120v circuit you have available. But it's working for you on the 240v wires and that's great.
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post #10 of 80 Old 08-08-2016, 02:05 AM
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Many years ago when I bought my first radial arm saw I had it sitting 10 feet from the panel and was trying to run it on 110 volts, I was ripping 1 1/8" plywood and the saw was continually overheating and cutting out. I went to the local service center to see if there was a chance of installing a larger motor so I could get some work done. The serviceman laughed and handed me a 220 volt plug and outlet and told me to install it the way it should have been done in the first place, worked like a charm.

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post #11 of 80 Old 08-08-2016, 05:20 AM
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Steve is right.

"When I have your wounded." -- Major Charles L. Kelley, callsign "Dustoff", refusing to recognize that an LZ was too hot, moments before before being killed by a single shot, July 1, 1964.
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post #12 of 80 Old 08-08-2016, 07:11 AM
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Quote:
Originally Posted by Brian(J) View Post
If you drag that compressor over to the panel and run a 120v circuit to it with #12 wire it would probably run better than it does now with 240v. Clearly there is a voltage drop issue with the 120v circuit you have available. But it's working for you on the 240v wires and that's great.
Can't disagree with that at all, Brian. But when it was wired for 120V it was sitting where it is now, 8' from the panel, and wired with #14. I need it sitting where it is and running so 240V was the quick and easy solution.

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post #13 of 80 Old 08-08-2016, 07:16 AM Thread Starter
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Again, the saw manual warns against wiring for 240 volts, however, I do not know if it is the original motor. The manual warns against using motors that are the wrong rpm, so it looks like I have quite a bit more investigation to do. (And here I thought I would just have to replace the blade)

My shop is currently split between the pump house and the barn. I laid wires to have 240 volts to the barn's sub panel, but the electrician that hooked things up did something that resulted in only 120 volts to the barn. The barn is 125 feet from the main panel. I remember the underground 4 wire was gosh awful expensive, 8 ga perhaps. The pump house has 240 volt service but is cramped at only 8 x 13 ft. so when I am done investigaing the motor, I may have to switch the saw to the pump house.

When I have the motor figured out, I suppose it is time to correct the problem with the wiring to the barn as well.


and all I wanted to do was cut some wood!

Last edited by holtzdreher; 08-08-2016 at 07:18 AM.
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post #14 of 80 Old 08-08-2016, 08:58 AM
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I'm curious as to why it cost less to run things on 240/220 volts.

I pay by kilowatts; watts = volts * amps.

240 motors have more starting torque/etc - but in the end it takes a certain amount of power to saw a board -
whether it's 3 amps @ 240 volts or 6 amps @ 110 volts seems to matter very little except for a possible slight difference in power factors.
other factors - size of wires=pounds of copper needed for more amps, line loss, etc apply - but outside of factory size shops, how much difference does this really make?
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post #15 of 80 Old 08-08-2016, 09:25 AM
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I'm curious as to why it cost less to run things on 240/220 volts.

I pay by kilowatts; watts = volts * amps.

240 motors have more starting torque/etc - but in the end it takes a certain amount of power to saw a board -
whether it's 3 amps @ 240 volts or 6 amps @ 110 volts seems to matter very little except for a possible slight difference in power factors.
other factors - size of wires=pounds of copper needed for more amps, line loss, etc apply - but outside of factory size shops, how much difference does this really make?
A motor uses magnetic fields to make it rotate. If only one field is used as in 110V it draws more amperage to get the job done than if it used two magnetic fields as in 220. You can tell this by the the heat the motor generates. It's the load you put on it doing woodworking. If the motor was on a bench not hooked up to anything the amperage would be the same either 110v or 220.
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post #16 of 80 Old 08-08-2016, 09:27 AM
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Originally Posted by holtzdreher View Post
Again, the saw manual warns against wiring for 240 volts, however, I do not know if it is the original motor. The manual warns against using motors that are the wrong rpm, so it looks like I have quite a bit more investigation to do. (And here I thought I would just have to replace the blade)

My shop is currently split between the pump house and the barn. I laid wires to have 240 volts to the barn's sub panel, but the electrician that hooked things up did something that resulted in only 120 volts to the barn. The barn is 125 feet from the main panel. I remember the underground 4 wire was gosh awful expensive, 8 ga perhaps. The pump house has 240 volt service but is cramped at only 8 x 13 ft. so when I am done investigaing the motor, I may have to switch the saw to the pump house.

When I have the motor figured out, I suppose it is time to correct the problem with the wiring to the barn as well.


and all I wanted to do was cut some wood!
I hope it's something better than 8ga for 125'...

#1 is most likely for a 125A sub panel.
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post #17 of 80 Old 08-08-2016, 09:30 AM
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A motor uses magnetic fields to make it rotate. If only one field is used as in 110V it draws more amperage to get the job done than if it used two magnetic fields as in 220. You can tell this by the the heat the motor generates. It's the load you put on it doing woodworking. If the motor was on a bench not hooked up to anything the amperage would be the same either 110v or 220.
Steve, all fields are used whether it's 120V or 240V, please try to absorb this, it's been covered a lot now.

All fields are used, the difference is how they are supplied, at 120V the circuit supplies all of the fields, at 240V they are split across the different 120V legs. That's why the current draw is 2x at 120V.
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post #18 of 80 Old 08-08-2016, 09:32 AM
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Originally Posted by holtzdreher View Post
Again, the saw manual warns against wiring for 240 volts, however, I do not know if it is the original motor. The manual warns against using motors that are the wrong rpm, so it looks like I have quite a bit more investigation to do. (And here I thought I would just have to replace the blade)

My shop is currently split between the pump house and the barn. I laid wires to have 240 volts to the barn's sub panel, but the electrician that hooked things up did something that resulted in only 120 volts to the barn. The barn is 125 feet from the main panel. I remember the underground 4 wire was gosh awful expensive, 8 ga perhaps. The pump house has 240 volt service but is cramped at only 8 x 13 ft. so when I am done investigaing the motor, I may have to switch the saw to the pump house.

When I have the motor figured out, I suppose it is time to correct the problem with the wiring to the barn as well.


and all I wanted to do was cut some wood!
125 feet is a long way to go with #8 wire. It's really only rated at 40 amps and going that far you may only be getting 35 amps. It really depends on how much you have going at once. If you have a lot of lights and or equipment you may be starved for power. You probably should have used #1 wire. You just need to add up everything you might have going at the same time and add a little.

Yes wire is expensive. It's why there are so many people going around pulling wire out of empty or abandoned houses.
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post #19 of 80 Old 08-08-2016, 09:36 AM
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Can't disagree with that at all, Brian. But when it was wired for 120V it was sitting where it is now, 8' from the panel, and wired with #14. I need it sitting where it is and running so 240V was the quick and easy solution.
#14 is the issue, even at that distance it should have been #12 for a 1.5HP motor.
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post #20 of 80 Old 08-08-2016, 11:09 AM
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Steve, all fields are used whether it's 120V or 240V, please try to absorb this, it's been covered a lot now.

All fields are used, the difference is how they are supplied, at 120V the circuit supplies all of the fields, at 240V they are split across the different 120V legs. That's why the current draw is 2x at 120V.
Nothing to absorb, there are two individual fields on a duo-voltage motor. You have the main winding and the auxiliary winding. When one is positive the other is negative when running at 220v. On 110v only the main winding is used for power.
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