110 or 220 for table saw

[Scott Welty]

I recently had the motor apart on my Jet Pro shop as the circuit breaker had truly broken. Easy to replace with new one from Jet and I noticed that I can easily wire the saw for 220 if I want. Since I popped the circuit breaker yesterday, loading the machine down by cutting long dado in a piece of oak, I started wondering if I help myself by wiring for 220. My high school physics says the Power = V*I so at higher voltage I get the same power at lower current. Yes? And current does the heating I think to pop circuit breaker.

Thoughts?

Scott Welty

[Matt Day]

This has been discussed before, but basically it's the same power output, but 220 is a bit more efficient (and cheaper by a minuscule amount). Some argue the motor runs cooler too.

[Cary Falk]

What is the amperage on the motor? Does your circuit have anything else running on it. The saw should run the same if you would run it on a dedicated 120V or 240V circuit. If you already have a 240V outlet then go ahead and switch it over.

[Rod Sheridan]

If you have a proper sized feeder (Which most 120V feeders are not), there will be no difference in motor performance.

People notice a difference in performance because they normally use an overloaded circuit with excessive voltage drop, when they convert to 240 volts they have a proper sized feeder and think the difference is due to the voltage change, it's not, it's due to having a proper sized feeder.

That said, I would always use the highest practical voltage to reduce the feeder wire size if possible..................Rod.

[John K Jordan]

What Rod said is right on, and circuits are often overloaded by using a wire size that would have been fine for a short run but too small for a long distance.

Four decades ago I converted a radial arm saw from 110 to 220 and the starting and performance improvement was significant. After doing the voltage drop calculation the reason was obvious.

I think considering the distance is the thing most people forget (or don't know) about when they wire things themselves. Besides the starting current, when motors are running under load the wire can heat, resistance increases, voltage drops further, wire gets warmer, ... My brother-in-law said he burned up several well pumps by running them on 110 on a long run. Switching to 220v over the same wire fixed his problem.

JKJ

[Dan Friedrichs]

Rod's got it right. Makes no difference to the motor (the same voltage is applied to the motor windings, either way), but higher voltage will reduce the current in the feeder. If the feeder is undersized, that may be desirable, otherwise, it won't make any difference.

[Scott Welty]

Thanks guys...I do have a longer than necessary cord running the saw. I'll shorten that up and I think I'll be ok...that and smaller bites out of the oak!

Scott

[Mike Henderson]

What's the HP of your motor? There's technically no difference between running a motor on 120 or 240, but from a practical point of view, I wouldn't run a motor any larger than 1.5HP on 120V unless you have a really good circuit with larger wire.

240V operation halves the current in the circuit, but limits your ability to move things around without rewiring. If you can run at 120V, you can usually plug in anywhere.

I run all my larger tools at 240V, but they're 3 to 5HP.

Mike

[Mike Hollingsworth]

I've never heard a downside.

[Rich Riddle]

Rod's right......oh that was hard to say.

[Ronald Mancini]

220 volts halves the current but produces the same power. Start current causes less light dimming because there is less voltage drop on the lines. The motor circuit breaker sees the same power regardless of line voltage, so one would assume that line voltage causes no difference in breaker tripping. Not always true because the 120 volt feed wire is often much hotter (twice the current) than the 220 feed wire so 120 can cause a higher breaker temp because of feed wire current. Always wire to the highest line voltage if convenient.

[Bill Space]

Hi,

One thing that never seems to be mentioned, is that if the circuit breaker feeding the motor, or the motor overload setting, is not adjusted after changing motor voltage from 120 to 240, then the motor can be worked harder, and more heat will be developed within it, than was the case when operating the motor on the lower voltage.

So depending on the duty cycle, rewiring the motor to operate on the higher voltage could result in damage to the motor due to overheating issues.

Probably not a concern if the saw is not used in a production situation.

So yes, upping the voltage does reduce current input to the motor, for a given developed HP, but keep in mind that if you work your saw hard the motor may get hotter than it used to.

Now if the motor has a thermal overload, this should not be a concern, as the thermal overload will trip the same regardless of what voltage the motor is operating at.

Bill

[Art Mann]

Bill, I think you need to do a little more reading on the subject you are discussing. Your comment does not make any sense to this electrical engineer.

[Jim Dwight]

Art,

I would not word it exactly the way Bill did but I think he has a point. If the overload protection for the motor is designed for 120V and you change the motor to 220V, there could be an issue. The overload protection would not work. But it is probably not a real case. I cannot imagine why a manufacturer would set the saw up for both voltages without the overload working regardless of how you hook it. I have a true 1hp motor (15A or a little more draw on 120V) that changes for 220V with just a couple wires moved. I would expect the overload to work regardless of how it is wired. But it could be something to pay attention to, especially with an inexpensive "no name" motor.

Jim (if it matters, my degree is mechanical engineering)

[Dan Friedrichs]

I think Bill is suggesting that if you had a motor wired with a separate (external) magnetic contactor and (external) over-current relay, you would need to change the setting of the over-current relay if you switched the voltage. That is true, but an unlikely scenario, since such devices (magnetic contactors with external over-current relays) are rarely found on <5HP motors, and a >5HP motor isn't likely to be dual-voltage.

If the motor has a built-in overload protection device, it would be wired such that the current through it is the same for either voltage, so you have nothing to worry about, there.

I suppose its possible to use a machine "harder" and get the motor hotter, in the process, but this has nothing to do with 120 vs 240 - it's just about having adequate supply. Sure, switching a machine from an under-sized 120v circuit to a 240v circuit may allow you to take a deeper/faster cut and get the motor hotter, in the process....but so would changing from an under-sized 120v circuit to a properly-sized 120v circuit.

In any case, not something anyone is actually likely to need to worry about...