There is a lot of confusion around the pros and cons between 120 volts and 240 volts in the wood shop. The reason for this is that electricity can be a very, very complicated subject! Fortunately, for woodworkers, it doesn’t have to be complicated at all. This article is not about industrial applications, three-phase power, line losses, motor efficiency, or any minute differences between these two options. My intention is only to offer sound, practical advice as it applies to the average home wood shop.
I see lots of different voltage numbers, what’s the deal?
The first thing you need to know is that household voltage in the US and Canada is supplied at about 120/240 volts. These are nominal numbers, and the actual voltage varies somewhat. But, with a few rare exceptions, the electric companies supply high-quality electric power to their customers. For practical purposes, the average woodworker should think of 110, 115, and 120 volts as all being interchangeable. Likewise, think of 220, 230, and 240 volts as being interchangeable. For this article, I refer to 120 volts and 240 volts, but the information applies equally to 110V, 115V, 220V, and 230V motors.
The motors in your shop probably have all sorts of different voltage numbers on them, but it’s not a big deal. Unless something is drastically wrong with either the power available in your shop or the motor itself, then motors that say 110, 115, or 120 volts will all run perfectly fine. Likewise, motors that say 220, 230, or 240 volts should all perform just fine.
This motor on my drum sander is an example of a typical 115V motor. It produces 1-1/2 horsepower, and it draws up to 14 amps.
Which is better, 120V or 240V?
Neither 120 nor 240 is “better” than the other, and neither is more efficient than the other. One might be better for a particular application, but neither is “better.”
To put it simply, there is no practical difference between a motor that is wired for 120 volts and the same motor that is wired for 240 volts. This is fundamental, and it is one of the few things that you need to know about the differences between these two. If you want more detail, the next two sections will help to explain this. If you just want to know how voltage affects you in your wood shop, and you don’t care about the “why,” then skip the next two sections and go right to the bottom line.
If you want more details, read on!
Motors, Volts, Amps, and Power
An electric motor produces “power,” and that power does the “work.” At its most basic level, power is expressed like this:
- Volts x Amps = Power.
- So, a 120-volt motor that draws 10 amps will produce 1200 watts of power. Therefore, a 240-volt motor that produces 1200 watts of power will draw 5 amps. (240 x 5 = 1200.)
Some motors, like this one on my Delta belt sander, can run on either 120 or 240 volts. You can see that it produces 1-1/2 horsepower regardless of the voltage that it is wired to run on. You can also see that running it on double the voltage decreases the amperage by exactly 50%.
This is the nameplate on the motor in my table saw, and it’s an example of a typical 230V motor. It produces 3 horsepower, and it draws up to 12.8 amps. This particular motor is designed to only run on 230 volts. Hypothetically, a similar 115V motor that produces 3 horsepower would draw up to 25.6 amps.
If 120v isn’t better than 240v, and vice versa, why are there two options?
Great question! It goes back to amperage. It’s also about industry standards and costs. Electric wire is rated for the maximum amperage that it will carry. Larger wires can carry more amps. A 3 hp motor wired for 110 volts might draw 25 amps. That would require relatively large and expensive wires from the breaker box to the receptacle. That same motor wired for 220V would only draw 12.5 amps and could run with smaller and less expensive wires.
A 120V circuit in most American homes are rated at either 15 or 20 amps. Typically, 240-volts is used if a particular load requires more power than a 20-amp, 115-volt circuit can provide. Examples of this would be an electric range or an electric dryer. Other examples of this would be stationary power tools with more than a 1.75 horsepower motor. (Don’t get me started on hand held routers that supposedly produce 3 horsepower!)
The Bottom Line
Whether it’s 120 volts or 240 volts, it’s horsepower that counts. There is no practical benefit to rewiring your 120V contractor saw to run on 240 volts. That will not affect how well it cuts through that nice piece of maple that you’ve been saving.
You can have a great wood shop and do wonderful work without 240V circuits. However, if you think that you might want larger stationary tools and if you have the option, then always include some 240-volt circuits in your wood shop. That’s because larger band saws, cabinet saws, planers, jointers, lathes, and dust collectors have larger motors that require 240V circuits.
It comes down to this: Rewiring your 120V 1.5 hp table saw to 240V won’t give you more oomph at the blade when you’re cutting thick hardwood. However, buying a 240-volt 3 hp saw, equipped with a motor that can’t be practically run on 120v, will give you more oomph.
Read information, I have just called my electrician to have him give me a 240 outlet for my “new” planner. Thanks for the tips
The cost is the same with 120 or 240, volts x amps make watts its the same
I approach the issue of 120 vs 240 volts from the supply perspective. My shop has 100 amp service. I have a central Air Conditioner/heat pump and a water heater which have high amp draws when they are running. By wiring my tools to 240 v, when possible, keeps me within the limit of my supply.
It makes no difference. A 240v 7.5 amp motor still uses the same number of amps as a 120v 15 amp motor. The only difference is that it is split between two hots instead of only one. Here is why: 240v 7.5 amp motor = two 120v hot wires each carrying 7.5 amps; 120v 15 amp motor = one hot wire carrying 15 amps. So both are using 15 amps at the panel.
There is a definite advantage to 240 volt power. As a motor loads up, the current increases. Ex. 3hp motor will consume approx 2250 watts (746w/hp x 3hp) at max load. Max current at 120v = 18.7a (2250w/120v) and 9.4a (2250w/240v). Motor resistance (R) decreases at max load to about 6.5 ohms (120v/18.7a) and about 24 ohms (240a/9.4a). The resistance of the circuit (wire, circuit breaker, and connection) remains almost constant. Therefore, the circuit resistance becomes a larger percentage of loss to the motor for the 120 volt source. Assume circuit resistance = .5 ohms. Voltage loss at 120v is 9v (18.7a x .5 ohms) and at 240v is 4.7v (9.4a x .5 ohms). Percent voltage loss at 120v is 7.5% ( 9v/120v) and at 240v is 2% (4.7v/240v). I have used my tablesaw in each mode and it definitely has more power at 240v (does not slow down like it did at 120v).
This was a really helpful description for someone who has a small shop with only 110V power at the moment, but with the ability to add 220V circuits as needed.
Excellent planning for future expansion. I had a small, 2 car garage shop that had both a 12 gauge, two wire 15 amp 110v for the overhead light and a 10 gauge, three wire 60 amp 220v circuit for the dryer. I tapped 110 off each leg of the 220 and ran two 110 circuits off the 220 around the three walls of the shop – all grounded. That way I could run the table saw, or the band saw, lath, or the jointer on one circuit without having to worry about the dust collector running at the same time, or the 4 hp air compressor starting up and overloading the circuit the machine was working with was on. I left the lights on the original 110 circuit and grounded it as well. For a small, one man shop, it was fine, considering the 110v equipment I had. I trained as a Power man (MOS 640) after basic training. I strongly suggest you consult with an electrical contractor regarding your shops needs for both now and for future expansion. Also, the codes are different and always expanding, so be safe and consult a professional – or “Here Lies ‘Sparky'” may just be the biggest memory you leave behind.
I converted my table saw from 120 to 240 and noticed a significant increase in the acceleration of the table saw motor. This makes sense to me because the initial rate of change in an inductive load such as a motor is directly proportional to the applied voltage. Fundamentally I believe that there is a significant advantage of 240v over 120v.
Your comment on “don’t get me started on 3 hp routers” shows you may know about volts and amps but not HP. HP is torque X RPM / 5252. so at a given torque, as RPM increases, so does HP. and at 20,000 rpm it only takes .8 lbft of torque to generate 3 HP. The amperage going through the electromagnets creates the strength of the magnetism generating torque. It is very different comparing a 3600 rpm motor to a 20,000rpm one when talking HP. At 3600 rpm it takes almost 5 lbft of torque, more than 5 times what the router has. More torque, more VxA.
I agree with all you have written. However; I believe (please confirm) evergy consumption is based upon usage on one leg, then doubled . In your high amp 120v tools are on one of the legs (not balanced between the two legs … which is only by chance) your power usage will be more than it would be if tools were wired for 240v. You are not using more power, you’re just paying more for what you are using.
Hi Larry. The calculation for energy consumed (power) is volts times amps. A machine wired for 120 volts that draws 5 amps consumes the same energy a machine wired for 240 volts that draws 10 amps.
The electric companies charge for how much energy is consumed whether the load is 120 volts or 240 volts.
Also, the amps drawn in each leg of a single phase circuit are the same whether 120 volts or 240 volts.
Paul
Woodworkers Guild of America
I think you mis-stated what you wanted to say.
120v x10A will give you the same wattage as 240Vx5A.
There is one difference you didn’t mention. In a cold climate where I live in Regina, Saskatchewan, Canada, my 120 v dust collector would often throw the breaker switch when my shop was cold, say around 50 degrees Fahrenheit. Switching to 220 v solved the problem. After about a year on 220 v and 6 years of use the motor burnt out. At 220 the dust collector did not have more oomph, but it always started without a hitch.
(My website – http://www.thecarpentershouse.love is under construction, and your field above won’t accept the entry apparently unless it’s a .com URL.) The big question for me is how do you know when you’re buying a 240V, 3HP saw, that can be run on 120V?? Where does the manufacturer make it explicit that a120V power supply will effectively power its 240V unit? I always thought that providing 120V to a 240V motor will decrease the power/efficiency, and you’re saying that’s not the case?
Hi William. Manufacturers list whether a machine can run on either 120 volts or 220 volts in the specifications. You can usually find this information on their website.
Unfortunately, rewiring a machine from 110 volts to 220 volts or vise versa has no effect on its efficiency.
Paul
Woodworkers Guild of America
I found a significant difference when using my table saw wired for 240 vs 120 especially when ripping hardwood. All my wiring is 12 gauge with 20 amp breakers and the runs are about 40 foot from the panel.
Excellent article! Short, to the point and actuate.
I agree with you on all but one point, sometimes a motor will get a “flat spot” like my compressor. Now I have to run it on 240v or unplug it turn the motor over a little than plug it back in and it will run until it stops on that one spot again
It might not be a flat spot, there is a centrifugal switch in the motor housing I believe controls the compacitor. It might be sticking a bit. It needs to be cleaned up or replaced.
You should keep in mind the startup draw required at 220 Vs 110 volts, and it’s effect on the motor being powered.
if you are drawing less amps with the 220 verses the 110 the are you saving electric used?
Hi Greg. Unfortunately, you won’t save electricity by changing from 120 volts to 220 volts. A 220 volt machine that draws 5 amps consumes the same power as a 110 volt machine that draws 10 amps.
Paul
Woodworkers Guild of America
Great article about the difference between 120 and 240 volts on smaller motors that can be wired either way. I would like to see an article explaining how small tools ie. a router can be considered 3 HP and draw lower amps at 120V. Thanks
Pretty good article, but to be clear…
Electric motors do not ‘produce’ power, they consume power to perform work.
It would help complete the subject to include wire conductor gauge requirements for common voltage and current combinations.
When using 120V most circuits should be alternated on both phases. This is called balancing the load. 240 V will balance the load for you. There are advantages for both. 2 – 120V circuits can be run on a 3 wire w/ ground if the neutral is shared on two phases. Power companies like to have balanced loads for distribution. Avoid voltage drop is best accomplished by using 240V.
The only issue I have come across is popping 20A breakers when my table saw, HVAC, dust collection and lights all are running. I have added another outlet with it’s own 20A breaker. I suppose I could have rewired the table saw to run on 220V and I assume that lower amperage would also solve the problem?
Hi Donald. Adding a new 20 amp circuit was a great way to address the problem. Rewiring your saw would have taken it off the overloaded circuit and it would have added it to a different 220 volt circuit.
Paul
Woodworkers Guild of America
i HAVE SEVERAL MACHINES I BROUGHT WHEN I LIVED IN CHINE AND SHIPPED BACK TO USA CHINA USES 220 VOLTS FOR EVERYTHING. IS IT SAFE TO PLUG INTO A 110 OUTLET? SAME AS MY GRIZZLY 3 HORSEPOWER 19 INCH BANDSAW CAN I PLUG IN TO A 110 OUTLET. LOOKING FORWARD TO HEARING FROM YOU. THANK YOU STAN MASHEK
Hi Stan. I wouldn’t plug a 220 volt machine into a 110 volt outlet. The machine probably won’t run and it could cause significant damage. Some 220 volt machines can be rewired to run on 110 volts. Take a look at the motor where the wires are connected. The motor will be clearly labeled if, and how to change it over to 110.
Paul
Woodworkers Guild of America
Thank you for your very interesting article.
One missing and very impetrate subject is the HZ – 50 or 60.
Your mails are reaching many customers overseas like myself.
If all goes well a 220V by 60 Hz will perform well but will lose about 18% of the rpm.
Many woodworkers purchased woodworking machines with a motor of 220V by 60Hz and faced problems requiring rewiring their motors in their country. You will be surprised of the luck of knowledge or the non-wiliness of major woodworking machines in the US to deal with issue. I just contacted Grizzly who I refer as a major supplier that could not give me a simple answer if one of their saws would run well on 220V by 50Hz. Their reply after supplying their saws for way over 20 years was – we never checked our motors on 220V by 50 Hz. an obvious reply to just cover their …. I recommend that you cover this issue as many of your readers are non-US or Canada woodworkers. Thanks, and best regards
A motor that is designed for 50Hz frequency will run faster at 60Hz. Consequence for this will be heat dissipation. For 60Hz motor that will run on 50Hz, it will run slower. It will also heat up since you cannot get enough torque due to lower rotation.
Thanks
I kind of agree with this write up. But volts x amps doesn’t = power it equals volt-amps. Power would have a power factor added into the equation to get watts. But you are correct the HP is what matters. 110V vs 210V doesn’t make a difference for quality of a cut or umpire of the saw but a high voltage is more efficient. Converting your 1-1/2HP motor from 110 to 210 has a major benefit. You will go from 10awg down to 14awg and go from a 35A 1P breaker to a 15A 2P breaker. There is a huge cost savings and the efficiency factor as well.
Power is measured in watts. Watts is literally the arithmetic product of volts and amps. That is to say, volts x amps = watts
Given this, I am not sure what point you were trying to make. There is no “power factor” required to find the watts.
Do you mean to apply a factor for efficiency? Because nothing is 100% efficient.
But your claim that 240 is more efficient than 120 is a miss. The motor will draw the current it needs at the provided voltage. We buy electricity in watt-hours. It will cost the same to run, which is the efficiency most people talk about in this context.
If you mean more efficient because the amp draw is half, so things run cooler, then you are correct there.
the one thing you did not mention is that 240volts is cheaper to run than the same hp at 120 because it uses less amps.
Maybe I’m wrong, but if one pays for watts used then that total won’t change by running at 240V?
Electric companies charge for “watts used”, not Amps.
> There is no practical benefit to rewiring your 120V contractor saw to run on 240 volts.
My last house was at the end of the line for power. My lights dimmed too much. If your lights are dimming too much, rewiring the saw from 110v to 220v changes from drawing 15a on 1 line to 7.5a split across 2 lines. This greatly reduced dimming of the lights in the house.
Another advantage of running at a higher voltage is the ability to use smaller cheaper wires. In your example of a 3HP motor, if it ran on 120V, the wire from the breaker box would need to be 8 gauge which is very expensive and a pain to wire up. While on 220V, 12 ga wire is sufficient and available at more hardware stores.
If your lights dimmed while starting your equipment.. the most likely fault the the transformer that services you house. As a kid we lived on a dead end road with one neighbor across.. when dad started his 1 Hp TS or the neighbor turned equipment on the lights dimmed.. Power company was called and they put tracking meter chart thing on our service .. power company replaced transformer- no problem of dimming afterwards
This article mentioned the key difference between 120 and 240 volts, the size of the wire required. Power loss and heat gain is proportional to the square of the current in the wire. So doubling the voltage drops the current in half and the power loss by a factor of 4. This is why power companies use extremely high voltage power lines to deliver more power over smaller wires. RT BSEE
Retired union electrician. Motor will last longer because amps equals heat. Heat destroys motors. Also the the motor will spin up faster, and have more grunt. Theory is great, but the magnetic force that turns the motor will be greater.
Your Comment is the same as the one I would have made. I am a retired Union Electrician as well. LU 322, Casper WY.
I agree with everything as stated. If you have 240 volts available in your shop and change you 120 volt motor to 240 volts, the motor should run cooler an the 240 volt circuit. The total power the motor puts our will be the same watts, but because the amp load will be half, the heat buildup will be less and therefore longer motor life.