[OP]
Member
I've always noticed that when I convert a machine over to 240v from 120v, it seems to have a little more snap to it when you hit the on button. Does that mean you have more torque? I tested it today in the same shop where everything I was connected to the same breaker panel outside and still noticed the difference.
Contributor
should not make any difference if the wire is correctly sized.
Bil lD
Contributor
What Bill said, no difference at all if it's wired to code
Member
IF you can provide full rated voltage to the motor in both cases then, as Frank and Bill said, there will be no difference. The problem is that it's harder to get good voltage regulation at 120V than at 240v. That is, even with wiring that meets code the wire resistance will have more effect at 120 than 240.
If Travis is testing only a short distance from his subpanel then most of the wiring resistance comes from the feeder. That resistance is the same at either 120 V or 240 V. So voltage regulation will be four times worse at the lower voltage. Torque varies with the square of voltage so torque loss will be eight times greater at 120 V than that at 240 V. Whether or not that's noticeable depends on the length and size of the feeder as well as the branch wiring.
Beranek's Law:
It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.
[OP]
Member
It wasn't that noticeable, but if you're listening for it then you can tell. Most people wouldn't notice.
Member
So you can conclude that your wiring is plenty adequate for 120 V operation of the motor. If you can barely tell the difference at startup you likely won't be able to notice anything in normal running where the current is much lower.Originally Posted by Travis Conner
For you then, the only real advantage to 240 V operation would be somewhat less imbalance current at your panel. The big disadvantage of course is the extra breaker slot it requires and the higher cost of ground fault protection if required.
Beranek's Law:
It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.
[OP]
Member
The panel is probably 35 feet from the transformer, then I have 2 gauge thhn wire running probably 30 feet to the 125 amp sub panel in the shop.
Contributor
I hope that 2 gauge is rated at 90 degrees. Even so it is only rated for 130 amps.
Bil lD
Contributor
If he exceeds 90 degrees Celsius he has bigger problems then that.
wireandcableyourway.com/2-awg-thhn-building-wire.html?gclid=Cj0KCQjwt4X8BRCPARIsABmcnOp_ZOthfn 43Y3iaGi0GpLa48HBTFDXmiKrgu68WwRLx_6xoCG0RrLEaAs6a EALw_wcB
Applications requiring Type THHN or THWN-2, the conductor is appropriate for use in wet or dry locations at temperatures not to exceed 90°C or not to exceed 75°C in oil or coolants.
[OP]
Member
Yes it is. I'm never going to be pulling a constant 125 amps anyways.
[OP]
Member
Bill most extension cords are only rated at 15 amps and people pull the full 15 amps all day long.
Contributor
This is a bit off subject but don't confuse torque and horsepower. Torque is a force while horsepower is a measure of work. While your motor starts up faster on 240V because of greater torque, it will not be able to do any more work than it could at 120V (assuming the wiring is correct). A 2HP motor is still a 2HP motor at either voltage.
Mike
Go into the world and do well. But more importantly, go into the world and do good.
Contributor
I bet if I fiddled with the wires and told you the motor was now connected for 240 volts you would notice the difference, regardless. Kind of like viewing N rays.
Bil lD
Member
The difference between the 120 vs 240 circuit is most noticeable on machines in a production environment where they are used for prolonged periods. The 120 volt wires heat up enough to cause more voltage drop. This is more of an issue in large production shops where cable runs are longer, no air conditioning and cables are inside conduits so you would want everything on 240V in those shops. Even wires to code will heat up.
Member
Surprised no one has gone to this yet, because I know I have seen the same in other threads...
120/240V motors generally have 2 windings (resistors). When the motor is wired for 120V operation, the windings are in parallel (and each has a 120V drop across it). When the motor is wired for 240V operation, the windings are in series (and each has a 120V drop across it). In both cases, its the same windings, same efficiency, same friction. And since the voltage drop across a given winding is the same in both cases, each case has the same potential for torque/work/horsepower.
If you have fairly long wiring runs, the voltage drop in the wire may be ever-so-slightly less significant at 240V - - and so the performance may be the same ever-so-slightly more better-ish.
It is possible someone might have a voltage sag on 1 leg of their 120V service, and so see improvement switching off of that to 240V, but the sag is easily measured .... and that's a whole 'nother rabbit hole.
************
Re-read Mr. Morse's post and he DID already describe this. - Sorry.
Last edited by Malcolm McLeod; 10-11-2020 at 1:52 PM.
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