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...

[Bill Space]

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.

Art,

Go back and read the post again. Perhaps your background is not in motor application and use. Perhaps my wording was poor.

The point I was trying to make was if the motor is protected by a built in thermal overload (like my old Craftsman saw has) then it is protected the same whether the motor runs on 110 or 220 volts.

If the only protection is an external circuit breaker, as found in a home shop, then there is opportunity to overload the motor without tripping the supply circuit breaker. The reason is because at higher voltage the motor will draw less current for a given amount of HP it develops. And current is what trips the external circuit breaker.

I was was not referring to an external starter as Dan mentioned, but agree if one is used, the overload heaters must be changed when motor voltage is changed. Good point Dan. This is something that should be kept in mind by those who have these controls.

Again, if the motor has a built in thermal overload there is no issue, as it is tripped by heat within the motor.

My logic is sound and the electrical theory is correct.

Hope it makes sensethis time.

Bill

[Lee Schierer]

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

It's not just the length of the cord, but the wire size that is most important. Most off the shelf cords are 14 gauge wire at the big box stores. You have to look really hard to find one with #12 or larger wire if they even have them. Make your own extension cord if you need one and buy #12 wire or #10 wire cut to the length you need and heavy duty plug and socket and you will get better results from your saw. This assumes that the wiring in the walls is properly sized for the run length.

[Lee Schierer]

I think what is trying to be stated here is that if you have a saw running on a 120 V circuit protected only by a 20 amp external circuit breaker that you could do damage if you rewire that same motor to run on 240 V and install a 20 amp 240 V breaker on that circuit. To properly protect that motor the circuit should be protected by a 10 amp breaker.


After thought....although this seemed like what he was trying to say, I don't believe this is the correct method for motor protection

[Dan Friedrichs]

As usual for any electrical thread we have, this one has taken a head-first dive down a rabbit hole of unlikely and esoteric possibilities, well after the OP has gotten the answer he wanted :)

Nonetheless, I'll pile on one last thing: the breaker isn't supposed to be protecting the motor, only the wiring and receptacle. The breaker should NOT be re-sized when switching the motor voltage. If overcurrent protection for the motor is desired, it should be supplied by an overload device on the motor (aka - the little red button that most motors have). But, even then, the likelihood of damaging a motor from overuse is extraordinarily small, anyways - I'm not even sure someone could manage it if they were trying.

[Malcolm McLeod]

...a head-first dive down a rabbit hole....

Soon after I joined SMC, I added my 2cents to a thread and was surprised when someone (sorry, can't attribute) said they refuse to join in electrical threads for much the same reason.

This is a shot of one of my many 'offices':
350924
My 'desk' is in the upper right corner.

I made the mistake of trying to bring what I know from an industrial perspective (24VDC thru 4160V/3Ph AC) and apply it to a residential garage. I failed. Lesson learned. ...Sort of.:rolleyes:

[Jerry Bruette]

Soon after I joined SMC, I added my 2cents to a thread and was surprised when someone (sorry, can't attribute) said they refuse to join in electrical threads for much the same reason.

This is a shot of one of my many 'offices':
350924
My 'desk' is in the upper right corner.

I made the mistake of trying to bring what I know from an industrial perspective (24VDC thru 4160V/3Ph AC) and apply it to a residential garage. I failed. Lesson learned. ...Sort of.:rolleyes:

What brand is your "desk"

[Chris Padilla]

... down a rabbit hole...

One of my profs in grad school liked to call them mink holes--because they feel all soft and cuddly thus causing one to keep diving....

[Malcolm McLeod]

What brand is your "desk"
It's a Rockwell ControlLogix. Now end-ith ye olde high-jack.:eek: ...Sorry, Scott!

[Art Mann]

Like I said, you really need to do a little more study on the subject, starting with your first assumption. If you reconfigure a motor for 240 instead of 120 VAC, you will not create the possibility that the motor will "work harder" or produce any more power. This has already been mentioned by others and is absolutely true.

The likelihood that a breaker will prevent a motor from self destructing under a mechanical overload or electrical fault condition is almost zero. This has never been the purpose of fuses or breakers. This has also been mentioned. I have written a somewhat lengthy discussion on this subject and will send it to you if you send me a private message with your email address. I would post it here but it is a bit long.

I know it is futile to keep having this same discussion over and over but I just hate to think that someone might be misled and do something dangerous or waste money due to bad information.


Art,

Go back and read the post again. Perhaps your background is not in motor application and use. Perhaps my wording was poor.

The point I was trying to make was if the motor is protected by a built in thermal overload (like my old Craftsman saw has) then it is protected the same whether the motor runs on 110 or 220 volts.

If the only protection is an external circuit breaker, as found in a home shop, then there is opportunity to overload the motor without tripping the supply circuit breaker. The reason is because at higher voltage the motor will draw less current for a given amount of HP it develops. And current is what trips the external circuit breaker.

I was was not referring to an external starter as Dan mentioned, but agree if one is used, the overload heaters must be changed when motor voltage is changed. Good point Dan. This is something that should be kept in mind by those who have these controls.

Again, if the motor has a built in thermal overload there is no issue, as it is tripped by heat within the motor.

My logic is sound and the electrical theory is correct.

Hope it makes sensethis time.

Bill

[Mike Henderson]

I think you guys are saying the same thing, but just in different words.

Mike

[Wade Lippman]

I think what is trying to be stated here is that if you have a saw running on a 120 V circuit protected only by a 20 amp external circuit breaker that you could do damage if you rewire that same motor to run on 240 V and install a 20 amp 240 V breaker on that circuit. To properly protect that motor the circuit should be protected by a 10 amp breaker.

I hope that isn't what he is saying! The breaker should never ever be used to protect the motor, and there is nothing wrong with a 10a (or 1a) motor on a 20a breaker.

Just couldn't let a 120/240 thread go by without comment.

[scott spencer]

If you have 220v readily available, I'd make the switch. There's no harm, little cost, and some potential gains. 220v has two hot supply legs that each carry half the current load....120v only has one hot leg that carries the full current, meaning that it's far more likely to be overtaxed. If your 120v circuit is somehow starving the saw for current, switching to 220v can reduce voltage loss and give the perception that you have more power simply by offering faster startup and recovery from bogging.

[Rod Sheridan]

If you have 220v readily available, I'd make the switch. There's no harm, little cost, and some potential gains. 220v has two hot supply legs that each carry half the current load....120v only has one hot leg that carries the full current, meaning that it's far more likely to be overtaxed. If your 120v circuit is somehow starving the saw for current, switching to 220v can reduce voltage loss and give the perception that you have more power simply by offering faster startup and recovery from bogging.

Scott, regardless of whether the supply is 120 or 240 volts, both wires carry the full current.

What you're probably thinking of is that the motor current at 240 volts is half of what it is at 120 volts......Regards, Rod.

[Mike Henderson]

If you have 220v readily available, I'd make the switch. There's no harm, little cost, and some potential gains. 220v has two hot supply legs that each carry half the current load....120v only has one hot leg that carries the full current, meaning that it's far more likely to be overtaxed. If your 120v circuit is somehow starving the saw for current, switching to 220v can reduce voltage loss and give the perception that you have more power simply by offering faster startup and recovery from bogging.
Absolutely not! Any single phase supply is over two wires and the full current flows through both wires.

I think many people get confused because one wire in 120V residential service is grounded. But just because it's grounded doesn't mean it doesn't carry current - it just means that it's at ground potential.

So whether you have a (single phase) motor which runs at 120V, 240V, 440V or anything else, the supply is two wires and the full current flows through both wires. There's no such thing as power in a single wire.

The reason a 240V circuit carries less current than a 120V circuit is that power is a factor of volts and current. If you reduce the current by one half, you have to increase the voltage by two to maintain the power. Or put another way, if you increase the voltage by two (from 120V to 240V) the current will be cut in half to supply the same power.

Mike

[Andrew R Miller]

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

WHat AMP is the breaker? what size is the wiring to that breaker? My entire shop is 115V I got somewhat lucky in my house that all the breakers are 20AMP and the correct wiring to support that

I don't have issues running tools of 20AMP extension cords to a 20A power strip, as long as I don't run more then one big draw tool at a time. (the real 20AMP stuff is expensive lol)

my DC is on a separate 20AMP, line from all that stuff I use the IVAC system to turn it on automatically and it works great!!!

[Von Bickley]

I am a retired Electrician / Instrument Technician. I have did residential work as well as industrial work. I try hard to never get into electrical discussions on a wood-working site.