220/240 volt advantages?

[Jason White]

Some people will say more powerful. Ignore those people. Advantages are blades come up to speed more quickly and less amp draw.

[Jim Morgan]

Thanks to all for the responses!

The concensus is that it doesn't matter to the motor whether it is wired for 110 or 220. But there is this from the 2005 thread that Lee Schierer referenced:

In my case the motor on my Delta Contractor's saw specifically states that it is 1 1/2 hp at 110, and 2 hp at 220. This was hottly debated on another board when a Delta rep was responding to messages and he was able to explain how it worked, but he was adamant that on my motor it would run at 2hp wired for 220.

Any ideas what was going on there?

Regarding the suggestion by Roger Wiegand and others to run 12/3 & then either use 1 hot+neutral+ground for 110 outlets or 2 hots+neutral+ground for 220 outlets, a couple of Code questions.
First, can multiple 110 circuits share a common neutral? Breakers protect the hot legs from overloads, but in the event that both hot legs were running just under full load, could the neutral get dangerously hot?
Second, how is the 12/3 connected at the service entrance? Using paired single-pole breakers could create a dangerous situation: shutting just one off while working on the circuit would leave the other leg still energized, with potentially fatal consequences. This must be prohibited by the code. But if a double-pole breaker is used, will an overload on just one leg trip it?

Finally, as Jim Becker points out, in a one-man shop, it doesn't matter how many machines are connected to a single circuit, so long as only one is in use at any time. As he says, some things should be on separate circuits. A dust collector for one (ftr, mine is on a dedicated 110 circuit). Also, shop lighting! If a machine trips a breaker, you would not want to be plunged into darkness - certainly not while sharp blades may still be moving.

[Mike Henderson]

Thanks to all for the responses!

The concensus is that it doesn't matter to the motor whether it is wired for 110 or 220. But there is this from the 2005 thread that Lee Schierer referenced:



Any ideas what was going on there?

Regarding the suggestion by Roger Wiegand and others to run 12/3 & then either use 1 hot+neutral+ground for 110 outlets or 2 hots+neutral+ground for 220 outlets, a couple of Code questions.
First, can multiple 110 circuits share a common neutral? Breakers protect the hot legs from overloads, but in the event that both hot legs were running just under full load, could the neutral get dangerously hot?
Second, how is the 12/3 connected at the service entrance? Using paired single-pole breakers could create a dangerous situation: shutting just one off while working on the circuit would leave the other leg still energized, with potentially fatal consequences. This must be prohibited by the code. But if a double-pole breaker is used, will an overload on just one leg trip it?

Finally, as Jim Becker points out, in a one-man shop, it doesn't matter how many machines are connected to a single circuit, so long as only one is in use at any time. As he says, some things should be on separate circuits. A dust collector for one (ftr, mine is on a dedicated 110 circuit). Also, shop lighting! If a machine trips a breaker, you would not want to be plunged into darkness - certainly not while sharp blades may still be moving.

This is possible if the motor contained a circuit that limited the current when operating at 120 volts. The motor could then be limited to 1 1/2 HP. When operating at 240 volts, the circuit could allow sufficient amps to genearate 2 HP.

There was a lathe company that did that with the motor they had on the lathe. If I recall, it was maybe 1 1/2 HP or 1 3/4 HP when operating at 120 volts and 2 HP or a bit more when operating at 240 volts. The reason for that limitation was that you can't get 2 HP worth of power from a 15 amp 120 volt circuit.

Mike

[Dan Friedrichs]

The concensus is that it doesn't matter to the motor whether it is wired for 110 or 220. But there is this from the 2005 thread that Lee Schierer referenced:
Any ideas what was going on there?

In that particular case, the motor is a 2HP motor, but Delta derated it (marked a lower maximum amperage and lower HP) for the 120V connection option. They did this so it could be sold with a 15A 120V plug. Had they left it marked 2HP and the higher amperage, it would have required a NEMA 5-20 plug, which most people don't have circuits and receptacles to support. With the correct 20A 120V connection, it would supply 2HP.

This gets a bit into the weeds, but a motor's rating is somewhat of a squishy concept, to begin with. It's just some tradeoff of cost, size, weight, performance, reliability, duty cycle, load characteristics, acceptable temperature rise, allowable operating ranges, etc. So nothing untoward about them deciding to mark it differently at a different voltage.

Regarding the suggestion by Roger Wiegand and others to run 12/3 & then either use 1 hot+neutral+ground for 110 outlets or 2 hots+neutral+ground for 220 outlets, a couple of Code questions.
First, can multiple 110 circuits share a common neutral? Breakers protect the hot legs from overloads, but in the event that both hot legs were running just under full load, could the neutral get dangerously hot?

This is called a "multi-wire branch circuit". Because the two hot legs are out of phase, the neutral carries only the imbalance between, which limits the max neutral current to the maximum difference between the two legs, which is the same as the breaker rating.

Second, how is the 12/3 connected at the service entrance? Using paired single-pole breakers could create a dangerous situation: shutting just one off while working on the circuit would leave the other leg still energized, with potentially fatal consequences. This must be prohibited by the code. But if a double-pole breaker is used, will an overload on just one leg trip it?

Correct, in a MWBC the breaker handles must be tied. Breakers with tied handles will trip both if either trips.

[Michael Burnside]

James, don’t over think it. There are a few exceptions, in this case sometimes a motor that supports both voltages will have a winding imbalance that isn’t double. The general discussion here is sound.

[Paul F Franklin]

It is possible to wind a motor with taps on the coils so that the number of turns used can be different when changing the configuration from 120 to 240. This could create a motor that delivers more power at 240 than at 120. One reason to do this would be to allow operation on a 15 amp 120 volt circuit (at reduced HP). So it can be done, but it's not common, and most dual voltage motors don't do it this way. The Nova voyager drill press has similar capability, but achieves it electronically, not with tapped coils.

Regarding the shared neutral circuit; it is allowed by code as long as a the two hots come from different legs of the 240 source and a 2 pole breaker is used. Because the two legs are out of phase with respect to each other, the sum of currents in the neutral is never more than the rating of one side of the two pole breakers. For example, if one leg is drawing 15 amps and the other leg is also drawing 15 amps, the current in the neutral will be zero. If one leg is drawing 15 amps and the other 0 amps, the current in the neutral will be 15 amps.

Shared neutral circuits were fairly common in my area for many years. They save a little money because you have 4 wires (2 hots, a neutral, and a ground) to serve 2 circuits instead of 6 wires if the two circuits were run separately. They are still allowed by the code, but have fallen out of favor for a number of reasons, one of which is the necessity for using 2 pole GFCI or AFCI breakers which tend to be a lot more expensive than 2 single pole GFCI or AFCI breakers. Also, I can't tell you how many times I have found shared neutral circuits that had be "rearranged" by someone not familiar with them such that both circuits were moved to the same leg of the supply. That *will* overload the neutral.

[Rich Engelhardt]

What plug did they come with? 5-15 or a 5-30? It would not surprise me if (a) they came with no plug and a 5-15 was added [ie., the wrong plug] or (b) came with a 5-30 and someone made an 5-30 to 5-15 adapter. Either way a portable compressor (especially targeted at field work by contractors) that required a 30A service, was a pretty silly design/machine. IMO.

They came in with a 5-15 plug.
The machines were obviously made in a foreign country and not thought out very well.
It was a silly design as well as a silly idea.
Like I said above though, a Builder's Square VP was heavily invested in the Puma line and he made sure that's all the stores were allowed to carry.

[Greg Funk]

I don't want to step on any toes, but there is no difference. Inside a standard motor capable of being wired for 120 or 240 are two sets of two coils. For 120 the two coils of each set get wired in parallel in the motor terminal block. For 240 they get wired in series. Each coil sees 120 volts no matter which way it is wired. The same current flows through each coil no matter which way it is wired. There is no difference in losses or efficiency *inside* the motor.

All of the points made in the thread about being able to run larger motors, using smaller wire, etc, are true, but the motor itself doesn't care or see any difference.

In theory, if all the wires feeding the motor and the internal motor windings had zero resistance you'd be correct. In reality, when a motor starts it can easily draw 6 time the FLA amps which, for a larger motor powered by 120V, can be 100+A. There will be significant voltage drops in the wires and the motor won't see 120V until it's started. Many years ago I had a 120V table saw that was slow to start. After re-wiring to 240V it would 'snap' up to speed much faster. Even when running under full load the 120V version of the motor will generate less power as the wiring losses will be higher for 120V.

[Anthony Whitesell]

In reality, when a motor starts it can easily draw 6 time the FLA amps which, for a larger motor powered by 120V, can be 100+A.

There will be significant voltage drops in the wires and the motor won't see 120V until it's started.

If there is more than a 6% drop in line voltage at the motor, then the branch impedence of the building wiring is too high thus indicating there is something wrong (corroded connection?) and an electrician should be called in to check things out before that high resistance connection causes enough heat to melt something.

Even when running under full load the 120V version of the motor will generate less power as the wiring losses will be higher for 120V.

There are two sets of windings in a 120V/240V motor. In 120V they are in parallel, in 240V they are in series. Being they are the same windings with the same resistance, dissapating the power, there is no difference in the wiring losses within the motor.

Therein lies one of the factors related to the difference in the startup speed. The voltage loss in the building wiring is less with 240V. Wire has resistance, and voltage loss is current * resistance. Less current = less voltage loss.

[Tim Greif]

Regarding those Delta motors rated at different horsepower, depending on whether it was configured for 115 or 230 volt operation, I have one of those saws and still use it today. You'll note that the current draw at 230 volt is more than half the draw at 115, so something is definitely going on here. it may well be that Delta derated the saw's claimed power at 115 so they could supply it with a 15 amp plug. I've always used the saw at 115 and have had no problems cutting anything. I firmly believe that unless the motor has completely different windings for 115 and 230 volt configuration, the motor will produce the same horsepower regardless of the voltage.
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