Up to and including 10HP, there is a high likelihood that commercial and small industrial facilities will have 208Y120V distribution systems, rather than 120/240V 3 phase 4 wire. It's also likely that the facilities are relatively small, so voltage drop from the service point is not likely to be large. Motor mfrs, knowing this, use a "compromise" design criteria for those smaller frames in that the motors are really 230V +10 but -15%. So they can run at rated load from 195.5-253V, and 208V -5% is 197.6V. This means at 208V they are still in spec, though they will pull more current to develop the rated HP, which means they will run hotter. The motors are made with a little more iron in them to absorb and dissipate that extra heat safely which makes them a litle more expensive, but the motor shops can carry less inventory to service the market. Large volume OEMs will often insist on saving that cash and using voltage specific motors and making the user adjust their feed, but off the shelf replacement motors don't need to do that.. The single phase versions of these really are 115/230V, but it's OK to use them at 208V if that's what you have.
Last edited by Jeff Raefield; 08-31-2015 at 8:55 PM.
A few years ago I was suing someone in small claims court. The judge was having difficulties; my explanation made sense, but I was just some schmo off the street and the defendant was an "expert".
The defendant said something really silly and I interrupted, saying that I had an engineering degree and I knew what he was saying was silly. The judge sat up and said, "so you're an expert?!" He was then comfortable ruling for me. I didn't have an opportunity to explain that while I had a BSE, I wasn't really an engineer.
That's funny Wade! I just left it at 120 for simplicity. It is however, the only device on the circuit, so it's not sharing an extension cord with 3 other devices any more. Yeah!
I had my bandsaw on a 110v extension cord with the dust collector. Right above the bandsaw was an unused 20a 220v outlet on a circuit by itself. For all the obvious reasons, switching made sense for me.
My experience has been that there is no difference between running the saw on 110 vs. 220. Running the DC and the saw without having to run to the panel has been a treat, though.
I resemble Dan's comment: the 120v run to my jointer was too long, and overloaded. So when I'd start it up, it'd take a 1/2 sec to kick up to full speed and would sag the lights meanwhile.
When I switched to 220, that problem went away.
It seems like it's easier to run more things farther away with 220. I like that.
Sorry to chime in on this at a late date. But I actually read this WHOLE thread! I’m a little scared of what that says about me. LOL. What I find interesting is that I’ve been unable to find a good visualization (video or dumbed –down diagram) of how this all works either here or on the internets.
So stop me if I get this wrong. I’m going to ignore the whole “starting winding” and capacitor factors. [clears throat]
In a dual voltage ac motor, you have two “motor” windings. Let’s compare them to Fred Flinstone’s feet in his stone-age car. When the winding is energized, it sets up a magical magnetic field thingy that makes the rotor want to spin. This is akin to one of Fred’s feet reaching down to the ground below him and pulling the car forward.
So – in a 117 volt setup, both motor windings are attached to the same wire, which is like Fred using both legs at the same time – lifting them both up in the air and stomping down on the ground and pulling them toward him in one motion – 60 times a second. The motor is getting 117 volts through each of its windings simultaneously, spinning the rotor with 60 two-fisted zaps every second.
In a 234 volt setup, the motors are attached to separate 117v wires from separate but equal sides of the fuse box. One motor winding gets zapped with 117v for 1/60th of a second and then the other motor winding gets zapped with 117v for the next 1/60th of a second. Sort of like Fred pedaling his feet in an alternating motion – like running.
Right?
So I get peoples’ argument that there is no difference, because the net power applied is no different. But I also understand why people say 234v is smoother, because spinning influence is being constantly applied to the rotor via the 2 motors alternately, instead of half of the time via both motors pulsing in unison.
What I DON’T get, is why we call it 234v, since each side is 117 volts (in my workshop) and the alternating pulses are … well, alternating …. and never added together. (Unless there is some push/pull thing happening that makes the voltage double, since one leg becomes the other’s return every 60th of a second – which I doubt since that seems like it would have some clear and major mechanical advantage.)
Nope, that's not how dual-voltage motors work. When a dual-voltage motor is connected to 120V, both windings (or groups of windings) are connected to the hot wire on the "front" end of the windings, and the neutral on the "back" end of the windings (a "parallel" wiring scheme). When connected to 240V, one hot leg of the 240V supply is connected to the front end of one winding, then the back end of that winding is connected to the front end of the second winding, then the back end of the second winding is connected to the second hot leg of the power supply (a series winding).
To your voltage question, they ARE additive, so while one hot leg is 120V positive in relation to ground, the other hot leg is -120V in relation to ground, adding to 240V between them (it's a little more complicated than that, as those are RMS--root means squared--voltages, so the peak voltages are actually about +/- 170V).
Sorry, not right. What you are doing in your thinking is looking at the voltages in each hot wire to ground (or neutral). But ground (or neutral) is not involved in the circuit. All you have is two wires with 240 volts across them. One sinusoidal voltage between two wires.
Jason has given a good explanation of how the motor is wired for the 120 volts and 240 volts.
Your view is a common misconception about power in a residential application. People seem to think of it as some kind of two "phase" system, with 120 volts for each "phase". That's completely wrong. There are only two wires delivering power to the motor and there is only one phase (or sinusoid) across those two wires.
Mike
Go into the world and do well. But more importantly, go into the world and do good.
There is a relatively convenient way to wire BS motor at 230V/1ph, but keep the attached task light on 115V.
The 'middle' leg of the motor wires, not the two hot 'feed' legs, is basically a neutral (where the 2 sine waves cross). You can get 115V between 1 of the hot legs to this middle leg. On some motors!!
And it beat$ pulling a neutral wire from the panel, just for a bulb. Be aware that it puts a small imbalance on the main 230V feed. So no 800W bulbs or 2hp feeders.
Just make sure to verify all of this with a meter, or call your favorite electrician.
Last edited by Malcolm McLeod; 09-03-2015 at 7:24 PM. Reason: typo