110 or 220 for table saw

[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':
panel.jpg
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.

[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':
panel.jpg
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.

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. ...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!!!