110 or 240 volt?

Mike,

It's not necessary to switch both legs of a 240 volt motor circuit provided there is a separate disconnect. Normally, one would use the circuit breaker as the disconnect in which case it is OK to use a single pole switch to control the motor.

My other comment on the 120 vs 240 volt supply for motors is that there is a fair amount of latitude given as to what constitutes acceptable wiring. According to code as long as the voltage drop under full load is less than 3% you are OK. Unfortunately, AC motors can draw up to 6x their full load rating while starting which yields a voltage drop of 18% during startup. That is why there are many anecdotal stories of people having much faster motor startup when they switch the motor and circuit wiring to 240V.

Greg
Well, you're correct in that you only need to break one leg. But people, including us, make mistakes and forget to turn that other switch off before we muck around with the motor. Let me put it this way - with my memory and attention span, I want a double pole switch.

I also want GFCI on all my shop circuits - but that's a different discussion.

The example you gave about the 3% drop works the same on both voltages. If you have a 3% drop on your 220 volt line and get 6x inrush current, the percentage voltage drop will be the same.

I think the reason you hear those stories is that people had marginal 110 volt circuits before they upgraded to a proper 220 volt circuit. When they do, the motor works better.

I hate to keep repeating myself, but if you feed the motor with a proper circuit, it will perform the same on either voltage.

Mike
 
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I don't believe the heat is the same. You will need twice the amps for 120v than you will for 240v for a given piece of wire. I don't see how you can run twice as many amps and not have more heat. In fact, I agree with you that heat per amps/power will be the same, but you're doubling the amps on a single circuit in the case of 120v, and that requires larger wire, as well as a larger breaker, and in turn my understanding is more heat.

Now the heat at the motor should be the same, either way, it is after all getting power to the motor and running it. Anyway, it's good to see this thread and there hasn't been any flames being tossed back and forth as has been witnessed on similar threads of other fora in the past. This is good.
Alan, let me give you an example using resistors. Suppose you have a circuit of one volt, with two 1 Ohm resistors in the circuit in parallel. One amp will flow through each resistor and each resistor will dissipate one watt for a total of two watts. Two amps will flow through the power source.

Now, let's increase the voltage to two volts but we'll put those two resistors in series. The current flow through the resistors is one amp and each resistor will dissipate one watt, for a total of two watts. Only one amp will flow through the power source.

In each case, the total power is the same and the heat is the same.

Motors work the same way.

Note that I'm talking about the heat in the motor and not the heat in the wires feeding the motor.

Mike
 
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I hate to keep repeating myself, but if you feed the motor with a proper circuit, it will perform the same on either voltage.

Mike
While technically you are correct this isn't very pragmatic advice. For one thing what is a "proper circuit". If an electrician wires a circuit to code it is quite possible a 1 1/2 HP motor will see a substantial voltage drop on startup. When this happens the logical thing to do is to change the circuit to 240V. When this happens they don't re-run the wires with a smaller size but they use the same size conductors which will have half the voltage drop and the motor will perform better on startup.

Greg
 
While technically you are correct this isn't very pragmatic advice. For one thing what is a "proper circuit". If an electrician wires a circuit to code it is quite possible a 1 1/2 HP motor will see a substantial voltage drop on startup. When this happens the logical thing to do is to change the circuit to 240V. When this happens they don't re-run the wires with a smaller size but they use the same size conductors which will have half the voltage drop and the motor will perform better on startup.

Greg
I don't disagree with you, Greg. I'm trying to make the point that 220 volts, by itself, is no better than 110 volts. If your wires cause too much voltage drop on 110 volts and you use the exact same wires to wire it up for 220 volts, you'll see less of a voltage drop - no argument about that at all.

A proper circuit is one that supplies rated voltage to the motor during all normal conditions of operation.

Mike
 
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And I think you're correct and what I typed in the last paragraph of my previous post.

Heat is and should be a concern with the wiring, and to ensure that you use the proper size wiring and connector/plugs so that one doesn't have a problem in the house. Many a homes burn down each year due to improper wiring. I think it's an important aspect of having a safe shop. I know you didn't say otherwise, I'm just pointing that out.
You're correct, Alan, but if the wires are heating to the point where you could have a fire, you're WAY out of code and have a very dangerous situation. I'm always making the assumption that you have a properly designed circuit feeding the motor, sufficient to carry the current without danger.

If the wires were heating that much, the voltage to the motor would be much lower than the rated voltage and the motor wouldn't perform very well.

Mike
 
It is also the same reason that 6 volt automobile systems were tossed aside in favor of 12 volt systems. And why large tractors and other hard to start engines use 24 volt systems.

And why locomotives use 2 sets of 32 volt batteries to start their 3000-6000 hp engines.

As a side note, hitching the two batteries together gives you 64 volts, but the entire locomotive electrical system is surprisingly comprised of 75 volts. For the interior lights and number boards they made special 75 volt bulbs, but in a pinch you could drop in a 115 volt standard bulb. It would not last as long, but would get the locomotive out of the engine house and pulling freight.
 
Everything that I have heard, been taught, or has otherwise been pounded into my head, says that the power concumption is the same. The breaker amp rating is half, but remember there are two legs on the 220 breaker. Wiring can also be lower guage for the same motor on 240 vs 120, because again the amp rating for 240 is 1/2 that at 120.
I did rewire my 1 1/2 hp Ridgid 3612 to 240 this summer. It does spin up to speed faster. Now, is that because of the lower voltage drop on start? Or is it because you have 2 legs of 120 that are out of phase with each other pulsing the motor windings instead of both windings having the same phase? Kind of like the old debate between a 2 cycle and 4 cycle engine performance. I don't know. I didn't take temp readings before and after to see if it runs cooler. :D Since I believe it is the same amount of power being used, I also believe the same amount of heat is being generated. But this is my opinion. I'm not a motor guru. YMMV. Jim.
 
I did rewire my 1 1/2 hp Ridgid 3612 to 240 this summer. It does spin up to speed faster. Now, is that because of the lower voltage drop on start? Or is it because you have 2 legs of 120 that are out of phase with each other pulsing the motor windings instead of both windings having the same phase?
Jim

Provided you kept the same size wires feeding the saw then yes it is strictly due to the reduced voltage drop. The motor will generate more torque and spin up quicker.

When you change to 240 you are still using a single phase. The motor simply sees a bigger sine wave.

Greg
 
Jim

Provided you kept the same size wires feeding the saw then yes it is strictly due to the reduced voltage drop. The motor will generate more torque and spin up quicker.

When you change to 240 you are still using a single phase. The motor simply sees a bigger sine wave.

Greg

Yes, I know that 120 and 240 is termed as single phase, but I was remembering that the 2 legs of 220 coming in from the pole were 180 out from each other. And the 3 legs of 3 phase were 120 degrees from each other. That could be wrong as so many ideas given by non experts (me!!:rofl:) get repeated until they sound correct. But I thought that was why 220 had to be one leg from each incoming hot, or otherwise you could combine any 2 hot wires and have 220, which as I understand it, is not necessarily a doable thing.
Mike, are you still with us?? Have you shrugged your shoulders and walked away yet????:rofl: Help me out here. Am I thinking of something similar but not stating the right thing?

I hope the OP got his question answered somewhere in here.:huh: Sorry we've ovretaken your thread for our collective higher education!! Jim.
 
The voltage on the two hots are 180 out of phase relative to the neutral but the saw doesn't see the neutral it just gets two hots. Relative to either of the hots the voltage on the other hot is 240V AC.
 
or otherwise you could combine any 2 hot wires and have 220, which as I understand it, is not necessarily a doable thing.

Jim,

If you "combine" any 2 opposite phase hot wires....by connecting them together.....Poof! :doh:

You have to have one 110V hot wire on one side of the load (motor) and the other 110V hot wire on the other side of the load. They will be 180 out, so the load will get 220V. You do not connect the neutral wire. It is a very good idea to connect the ground (green) wire to the frame/motor case for safety (in case one of the hot leads ever came loose and touched the metal.
 
Greg F. is generally correct. The way power is fed to your house is that the power company puts in a transformer that steps a single phase of the three phase power that is on the grid down to the voltages that you see in your home.

So the primary winding of that transformer is a single winding with two ends.

The secondary winding (the side that feeds your house) is a single winding but it is center tapped so three wires are brought out.

The voltage on the secondary of a transformer is determined by the ratio of the number of primary "turns" (how many times the wire goes around the core) to the number of secondary turns. So if you have a lot of turns on the primary and few on the secondary, the transformer is a "step down" transformer - the voltage across the secondary will be less than the voltage on the primary. The transformer that serves your house is a step down transformer.

The turns ratio is set so that the voltage across the two "outside" wires of the secondary will be about 220-240 volts. But that winding is "center-tapped". So, for example, if the secondary has 200 turns, a wire is connected to the 100th turn and brought out. If 200 turns will produce 220 volts, 100 turns will produce half of that, or 110 volts.

In our system, that center tapped wire is connected to ground. There's good reasons for having a ground connection but I won't discuss that here. Some European systems do not have a ground and that provides certain advantages and disadvantages. Ask me about that and I'll give a long explanation of the advantages and disadvantages of grounding.

But I digress... Those three wires from the secondary are brought into your home and become the two "hots" and the one neutral in your box.

So... the power across the two hots is single phase 220 volts, and the power across one hot and neutral is 110 volts single phase.

To get three phase power, the power company has to put in three transformers, one for each phase. It's more expensive for the power company but is really worth it in industrial settings.

Mike
 
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Three phase power on the grid...where the heck do you guys live????

Here in Maine you got to live right next to a sub-station or next to an industrial park to have three phase on the pole. I was just noticing today that a local pipeline is installing a new pumping station, and they had to install 3 phase power for miles alongside the road in order to get it there.

Man am I ever jealous of your 3 phase ease. Of course I also live on a road that has intermittent pavement (some is gravel/ some is pavement) and three houses from me, the power lines just stop for lack of houses to supply. :D
 
Gee - "power on a pole"? In my neighborhood it's all underground. :D

(Which was actually kinda hard for me to get used to when I moved in.... :huh:)
 
Greg, I guess I should have said "use" the hots of two 120 circuits to make a 220 circuit, not combine them. I was typing at work, and didn't think through the possible readings. :type:
Ok, the answers to my questions make me feel that I did have the right understanding. Use of the right terms may still be questionable. :) Jim.
 
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