I recently purchased a Hitachi C10FL table saw. It is a 15A saw & comes from the factory wired for 120V. It came with simple instructions for rewiring it for 240V (which means it would draw 7.5A)
This seems desireable to me since the greater voltage (and reduced draw) would seem to make for better performance. What would be the drawbacks of switching it over to 240?
The main issue I see is that the saw has a normal 3 prong 15A plug – while this poses no problem for wiring an outlet for 240 & plugging it in, I’d be concerned that someone might plug some other appliance into the outlet & fry their equipment – is it a simple issue of labeling the outlet as 240V? I’d wire a single dedicated outlet in this case…
Replies
Never, ever wire a concentional outlet as 220v! They make special outlets for 220; use one. Get a replacement plug that fits and replace the plug on the saw with a 220v plug. Not much $'s, and totally safe!
Brooks
That's a good idea.It seemed strange to me that they didn't include an alternate plug in the package - since the saw is advertised as 120/240 & they include instructions on how to switch it over.
For 240 vac you'll have to change the cord and the plug since you'll need four wires instead of three.
What does the 4th wire go to in a table saw?Pete
Isn't there a neutral to provide 120V for the little lightbulb and the timer?
No, wait, that's for an electric range....
Nah, ya don't need four wires for a 240V motor. Like was said, two hots and an equipment ground (that equals three in my book, but then again, I was in school long before the "new math" came to be...)
Ya do need four wires for a 240/120V appliance, like most electric clothes dryers and ranges. The heating elements run on 240V (most of the time, although I think some fancy cooktops have a 120V element for low heat), and the timer and lightbulb work on 120V.
Cliff
p.s. I agree, converting the saw to 240V will be good in that it'll minimize voltage drop, the motor will run cooler, and last longer. And here's another vote for installing the right receptacle and cord cap. C.
Why would you need four wires? For 240, you'd have two hot legs & a ground.
Four wires are for appliances that require 120 AND 240 voltage (such as stoves or driers). They'd need a neutral leg for components that need only 120.
You're right, of course.
I must have had a momentary disconnect.
I think 240 is generally better simply because when people switch to a 240V circuit, they typically upgrade the wiring. Like using 12 gauge wiring instead of a typical 14 gauge 15 amp circuit. The larger wiring makes the difference.I can't say 100% for sure that's true. But it's the only explanation that made sense to me about 240 being better. I don't believe it makes a bit of difference to the motor otherwise
My tire was thumping
I thought it was flat
When I looked at the tire
I noticed your cat.
What they said about the outlet. Follow the directions closely. I blew a starting capacitor up once by missing a required step. Quite the fireworks!
All that said, is it helpful to switch it over? Am I correct that 240V will provide better performance?
I imagine they ship set at 120V since not everyone has a 240V outlet in their shop/basement/garage.
I don't think that 240 will provide better performance in the saw. What it will do is spread the current out over two circuit breakers instead of one, so you won't be remotely close to tripping a circuit when you run the saw.
I don't think the motor will put out an ounce more power than it would w an adequate 120v source. You could, however, find a motor w the the same frame size, 240v, single phase, that would put out more power. Or even,,,,,, do you have 480 in your shop ?????
H
I realize that the motor won't put out more power, but given that the draw is cut in half, I'd experience less voltage drop.
Would that be an issue? The saw plugs in ~20 feet from the panel (20A circuit, #12 Cu), however, my house is ~300 feet from the transformer (200A service & I ran 250KCM Al for my service entrance).
It's not that difficult to switch it over, but I don't want to do it just for the sake of doing it.
The 240 would be better, but not a lot. You are right about the voltage drop, but at 20 feet from your panel it wouldn't be much. The 200 feet to the panel would matter even less since the leads to the panel are much bigger (unless all of your other circuits are always drawing close to the max for those leads. It is a good thing to keep your load balanced on your panel and anything running on 240 does this by nature.
Anyway, I think, the main reason for switching to the 240 is that it is better for the motor itself. The reduced current going through it will generate less heat, thus put less strain on it. Once again this is probably not too big of a deal since the motor is designed to work, and cool itself properly on either voltage.
If it were me, I would switch it to the 240 if I really planned on not moving it anytime soon. I would leave it alone if I thought I might want to use it in a different place occasionally.
If this is a dedicated circuit, you've got a 15 amp saw running on a 20 amp circuit over 12 guage wire. Right? 20 feet isn't that far, so I don't think voltage drop should be a problem, but I think this is right at the threshold of what is ideal. You can switch over to 240 and have a large "safety" buffer, but it will probably be just fine if you leave it at 120. If it were me, I would switch to 240. It's what I did with my table saw, but it's probably not needed.There's a really good discussion of this exact question over at: http://www.thewoodshop.20m.com/faq.htm"I agree that it is generally better to run the saw on 240 volts, but would offer different reasoning to do so. Your explanation stated that ... “you can starve your motor for amperage which will damage it sooner or laterâ€. Actually, as long as the motor is running, it will not be “starved for amperageâ€. A motor draws whatever current is necessary to produce the necessary torque to maintain speed. The limiting factors on how much current the motor will draw, are the wiring circuit breaker rating, the motor’s thermal cutout (if so equipped), and the LRC (Locked Rotor Current) rating on the motor’s nameplate. What actually happens in situations where there is excessive wiring resistance is that the supply voltage at the motor terminals drops below the nameplate’s acceptable value (usually 105 VAC). When the available voltage falls, the motor can start to “slip sync†under load. This just means that the rotating armature can't keep up with the rotating magnetic field and begins to fall behind and is, therefore, out of synchronization with the 60 Hz power line frequency. The bad part of “slipping sync†is that the motor’s efficiency falls off drastically when this happens. Efficiency is the term that says what percentage of the input power gets converted to mechanical power. The remainder of the power is “lost†which means it gets converted into heat. In order to try to maintain synchronous speed, the motor will draw more current to produce the necessary torque. But, when the efficiency is low a large part of this current goes into heating the motor. So, you can see that rather than being “starved for amperageâ€, the motor is actually drawing MORE current than it would if operating efficiently. And that is what can lead to eventually damaging the motor.Voltage drop in the wiring is not normally a significant issue – but it can be. A wiring run of 12-gauge wire that is 90 feet or less in length and drawing 20 Amps would result in no more than a five percent drop in voltage (about 5.8 volts). However, a motor should not be operated on a circuit in which its FLC (nameplate full load current) is that close to the circuit breaker rating. If it is a dedicated circuit for the tool, then the NEC or other applicable code should be consulted for breaker size. Otherwise, for a motor on a non-dedicated circuit, 15 Amps FLC should be the absolute maximum that you use on a 20 Amp circuit. For me, the most important issue is to have a circuit in which the motor’s FLC is well below the breaker rating. Normally the best way to accomplish this is to operate the motor on 240 VAC. This solves the problem of voltage drop in the wiring and also allows plenty of headroom for the breaker size.The cause of the large surge in motor current during startup is often misunderstood. The current surge is the result of torque needed to accelerate the motor’s inertial load. Motors have an extremely high acceleration at startup - going from standstill to full speed in a few tenths of a second. The inertial load consists of the armature’s moment of inertia, the gear train moment of inertia, and the load moment of inertia reflected through the gear train. The torque that the motor needs is the product of the acceleration and the total moment of inertia and can be extremely high. Motor current is directly proportional to torque so it can be seen that there will be a very large surge in startup current."
"When the available voltage falls, the motor can start to “slip sync†under load. This just means that the rotating armature can't keep up with the rotating magnetic field and begins to fall behind and is, therefore, out of synchronization with the 60 Hz power line frequency."Not exactly.This is an INDUCTION MOTOR and it always has some slip. The slip between the rotating stator field (60 hz => 1800 rpm 2 pole, 3600 rpm single pole) and the speed of the rotor generate (induction) the current in the rotor for the opposing field with causes the forces to move the rotor.The motor will be speced for something like 3450 rpm at full load. Thus a slip of 150 rpm.However, when the motor is overloaded the slip starts increasing drastically until the motor stalls. When it stalls you don't have an counter EMF and the current draw is drastrically increases.Been WAY, WAY, WAY, WAY TOOOOO LONG to remember and to go through by Electrical Machinery text to see what happens between normal load and stalling.The only place that you will find synchronous motors in a home are on clocks, timers, and turntables. And very few, if any days."The cause of the large surge in motor current during startup is often misunderstood. The current surge is the result of torque needed to accelerate the motor’s inertial load. Motors have an extremely high acceleration at startup - going from standstill to full speed in a few tenths of a second. The inertial load consists of the armature’s moment of inertia, the gear train moment of inertia, and the load moment of inertia reflected through the gear train. The torque that the motor needs is the product of the acceleration and the total moment of inertia and can be extremely high. Motor current is directly proportional to torque so it can be seen that there will be a very large surge in startup current.""True, but for something like a table saw the starting load is fairly small. Besides the rotator all you are rotating is a pair of small pullies and the blade. Not much of a load until you start cutting.How things like compressors (either air or refigerant) will have much larger starting currents since they are starting against a load. "Voltage drop in the wiring is not normally a significant issue – but it can be. A wiring run of 12-gauge wire that is 90 feet or less in length and drawing 20 Amps would result in no more than a five percent drop in voltage (about 5.8 volts). However, a motor should not be operated on a circuit in which its FLC (nameplate full load current) is that close to the circuit breaker rating. If it is a dedicated circuit for the tool, then the NEC or other applicable code should be consulted for breaker size. Otherwise, for a motor on a non-dedicated circuit, 15 Amps FLC should be the absolute maximum that you use on a 20 Amp circuit."Actually for things like a table saw you can usually do this without any problems as long as the drop in the wiring is low.Most breakers are time inverse and will handle fair amount of overload for a short time.And the average load on a table saw is fairly low.Now you are cutting 3" hard maple and a powerfeeder and have them stacked up then you are right. Something like that really needs a dedicated motor circuit with approprate breaker sizing.
Here's a whole bunch of good tech info on motors:
http://www.baldor.com/pdf/literature/PR2525.pdf
-- J.S.
I don't think the motor will put out an ounce more power than it would w an adequate 120v source.
Your right, it won't. The motor windings don't even see an difference; it's just in one case they are wired in parallel, and in the other they ar wired in series.
The gotcha is the "adequate 120v source" thing. The one big advantage of using 240v is that it makes most people install a 240v circuit for the tool. Combine this with the fact the the current draw through the circuit wires is less, and thus smaller guage wire is needed to avoid excessive voltage drop, means that a 240v circuit is very likely to adequately supply the saw.
In contrast, the tendancy with 120v tools is to just use a receptacle on an existing 120v general-purpose circuit, which often isn't up to the task. Excessive voltage drop results.
Every tool maker and electric motor company rep I've talked to suggested running at the higher voltage if one had the option. Some use the phrase "do your motor a favor". This is especially true for 1.5 hp and larger motors. At 220 or 240, the current draw is half as much (that's why it doesn't trip breakers as often, not because there are 2 of them). The motor runs a bit cooler. Also, voltage drop across the feeding wires is less, so the motor has close to the full 220 even at the end of a long run (e.g an extension cord).
Only drawback as mentioned by others is if a 220 outlet isn't available/handy in many locations.
Less amp draw is better. Use the proper recepticle though.
I have always run my switchable shop motors on 220. More efficient, and a much quicker and smoother startup. You will like the difference.
A 220V plug or receptacle has one prong vertical and the adjacent prong horizontal, with the "ground" prong (think elongated half circle in profile) per usual.
I switched a unisaw over to 240. started up a lot quicker, and dimmed the lights much less. I'd recommend it. The twist-lock plugs are nice- your saw won't work itself unplugged over time.
zak
"When we build, let us think that we build forever. Let it not be for present delight nor for present use alone." --John Ruskin
"so it goes"
Put in a 240 volt outlet and change the saw over to 240. You will be glad you did. It cuts the voltage drop in half, which really means that the percentage drop in voltage is cut to 1/4. It equates to much faster start up and a lot less strain on the motor.