120 vs. 240 volts for shop motors

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Forum topic by TopamaxSurvivor posted 01-24-2011 10:53 AM 3376 views 5 times favorited 17 replies Add to Favorites Watch
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24657 posts in 5138 days

01-24-2011 10:53 AM

Topic tags/keywords: 115 120 125 130 220 230 240 vs voltage motor table saw band which tablesaw bandsaw power electric bill efficient change amp amps current high higher low lower best way wire capacitor test single phase hp horse horsepower 1 hp 1 12 15 2 3 5 lights blink blinking percent drop starting flickering incandescent fluorescent transformer motors start

Seems this is a constant subject of debate here on LJ. I thought I would add a little to what I posted on a motor thread and post it with a lot of search tags.

I have been doing mostly motor and control work for 43 years. I don’t know much about plugs & lighting and really don’t much care about it. Anybody can install outlets or hang light fixtures all day. The little bit of that type of work I have done was enough to last me a lifetime. ;-)) If you have more than 3 % voltage drop when starting your motors, you will see it flickering incandescent lights. If it is 5% or more, you will probably see it in fluorescent lights. Depending on how far you are from the transformer that serves you, some slight flickering may be unavoidable when motors start.

The bottom line on single phase motors; @ 1 hp & above consider wiring 220, 230, 240 (what ever you want to call it, your preference, its all the same thing).

If there is a noticeable lag in starting the motor of any size or voltage, it will eventually be damaged by that starting pause. It may take many years for it to show, but it will be damaged. The current goes up from 5 times to infinity during that starting pause. It is already at lest 5 times the running current during starting unless you have a soft start. High current means more heat; more heat means insulation break down; insulation break down means short circuiting in the motors winding; that, of course, means the end of the motor’s useful life.

There is really no reason for any properly made electric motor to ever fail with the exception of the capacitor or starting switch on single phase motors or the bearings on any motor. Properly started and loaded, they will, literally, last forever.

A watt of power is a watt of power whether it is at 120 single phase or 480 3 phase. From a power bill standpoint, it does not matter which voltage you use.

The little bump or bumps on your single phase motor is the capacitor(s). One for capacitor start and 2 for capacitor start capacitor run. It just gives the motor a little push in the right direction to get it started.

Capacitors can be checked with a multi-meter (VOM) or, a small DC current such as a 6 volt battery series. They definitely will hold a charge. You discharge them by shorting across the connections with a screwdriver. What ever happened is ok ;-) Even if you jump, it is still ok ;-)) Most capacitors these days, have a built in resistor to take care of any remaining charge, but don’t rely on it.

To check a capacitor you charge it with a voltage from a VOM or a few batteries. Watch for a faint little spark when you short it if you used 3 or 4 batteries to charge it. It is good if you see a spark. With a VOM, place the leads on the terminals with the meter on the ohms setting. Leave it for a minute or 2. Watching the meter, reverse the leads, if the meter shows little blip, the cap is good; if not, no good. Watch close, because you can easily miss it. Old analog meters with a needle movement are much easier to see than the new fancy dancy digital meters. Matter of fact, they are better for most trouble shooting applications of power and motors. Digitals have a habit of misleading you if you are not aware of how they operate. Most cheap digital meters will not show the capacitor as being good because they do not react fast enough. Meters like Fluke which have an analog bar on the display will show you what you what you want to know.
Capacitors can be replaced with another that is close in size, does not have to be exact. The voltage rating has to be as high or higher or it will short out.

If there are oil caps on the bearings, put a few drops of Rislone in there once a year with a few drops of light machine oil. About the only thing you can to a motor to destroy it is over load it, over lube the bearings or over stress the bearing by running things too tight or at an odd angle. Remember just don’t over do it and it will last longer than you will. Few = < 5!!!

Reminds me of a burned up motor I found in a steel plant. The motor had zerks on the motor bearings. This was an old 25 hp +/- from the 60s or earlier. They greased the machine every shift, including the motor ;-(( Grease must be a very good heat conductor because it was packed full and no air could circulate to cool it ;-))

Standard disclaimer: This is not intended to make the novice an electrician. The intention is to inform you enough to know if the electrician you are using knows as much as you do now and enough about motors to be trouble shooting them.

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

17 replies so far

View sawblade1's profile


754 posts in 4488 days

#1 posted 01-24-2011 11:17 AM

Great subject Topamax also great tip :) Another thing to consider working From working in industrial maintenance is to Properly size the circuit bigger than normal as such in my case running 50 amps out to a back fed sub panel with a 50a breaker and feeding 20amp Breakers separately for my larger Hp motors as a capacitor start induction motor rated @ 15 amps will pull 17.5 for 5-6 seconds during start up !!!! By doubling the voltage you cut the amps in half :) lessening the overall load on the motor which also in turn contributes to the healthy life of the motor :)

-- Proverbs Ch:3 vs 5,6,7 Trust in the lord with all thine heart and lean not unto your own understanding but in all your ways aknowledge him and he shall direct your path [email protected]

View TopamaxSurvivor's profile


24657 posts in 5138 days

#2 posted 01-24-2011 11:30 AM

Yeah, I could have gone into circuit sizng and subpanels, & ..................... Subject for another night :-)) bedtime!!

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

View canadianchips's profile


2632 posts in 4459 days

#3 posted 01-24-2011 02:47 PM

Thanks Topomax.
I did know some of this, YET I am guilty of doing things in my shop. (Out of necessity) The long extension cord I use is my pet peeve.
The little shop I have now was previously used to store a car only. It had 1 light bulb hangin (litterly hanging by wires) from ceiling and 2 electrical 110 volt plugs.(Each on its own 15amp fuse) The power comes from the house (shared with bathroom circuit) into a double fuse panel in shed. The shed is about 15 feet from house.When she uses her hair dryer and I am trying to cut on table saw, I am walking to house to re-set breaker.

-- "My mission in life - make everyone smile !"

View CharlieM1958's profile


16292 posts in 5680 days

#4 posted 01-24-2011 03:17 PM

Very informative piece you’ve written, Bob. Now I’ll sit back and watch the sparks fly. :-)

-- Charlie M. "Woodworking - patience = firewood"

View HorizontalMike's profile


7935 posts in 4376 days

#5 posted 01-24-2011 03:25 PM

Hey Topa, does this now make you a ”tagger”? LOL!

But really, this post is long over-due. Thanks for taking the time.

-- HorizontalMike -- "Woodpeckers understand..."

View Gregn's profile


1642 posts in 4445 days

#6 posted 01-24-2011 04:18 PM

Great post, I use to think 120 was all one needed in the shop but with a lot of the motors being able to be connected to either way. I have opted to wired for the 240 voltage instead for those motors that have that capability. Thanks for the great information on capacitors and voltages.

-- I don't make mistakes, I have great learning lessons, Greg

View TopamaxSurvivor's profile


24657 posts in 5138 days

#7 posted 01-24-2011 08:05 PM

You’re all welcome. I guess it looks like I’m a tagger for sure now!! :-))

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

View Loren's profile


11506 posts in 5110 days

#8 posted 01-24-2011 08:13 PM

Good stuff. I learned a lot from that.


View ClayandNancy's profile


532 posts in 4477 days

#9 posted 01-24-2011 09:13 PM

I’ve swapped all the machines that are capable of 220 over. I have a question on 3 phase, I’ve been looking for some additional machines for the shop, a lot cheaper in 3 phase and see all sorts of voltages listed as 3 phase. One that confuses me is 220 3 phase, is that right? Is there machines that have dual voltage 1 and 3 phase?

View PurpLev's profile


8654 posts in 5110 days

#10 posted 01-24-2011 09:31 PM

great post Bob, thanks for the info.

I would love to hear more about subpaneling and what it requires (upgrading main panel? changing incoming wires?...etc)

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View Dennisgrosen's profile


10880 posts in 4577 days

#11 posted 01-24-2011 10:06 PM

thank´s for a very informative blog Topamax
learned it 30 years ago and forgotten 29 years ago…..LOL
thank´s for the reminder :-)

take care

View Knothead62's profile


2600 posts in 4423 days

#12 posted 01-24-2011 10:14 PM

Three phase has an extra wire; one more than 220V, single phase, which has two hot, one common and one ground. You would need an electrician for the 3-phase wiring. As for the last question, I’m not sure. Topamax might have the info here. BTW, Top, thanks for the tutorial on electric motors.

View teejk's profile


1215 posts in 4146 days

#13 posted 01-24-2011 10:43 PM

3 phase “comes from the pole” so it may or may not be available to everybody. Too bad because many of the nice used machines are 3 phase. As for converting single phase to 240v, it does seem to make the machines run smoother (it might be in my head). Some machines (not all) will require changing the factory switch ($$$!). I know that to be true for my Delta contractor saw and jointer.

View TopamaxSurvivor's profile


24657 posts in 5138 days

#14 posted 01-25-2011 02:26 AM

ClayandNancy I started to answer you question about 3 phase, but I suppose I may as well do this: The answer is over there :-))

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

View lanwater's profile


3113 posts in 4396 days

#15 posted 01-25-2011 08:21 AM

Great topic.

My dust collector can run either on 110v (factory setting) or 220v.
the rated noise is 74db at 1o feet away.

Do you know if switching to 220v lower the noise?

-- Abbas, Castro Valley, CA

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