Wiring Question

[Brian Triplett]

Hello all,
Question for you about wiring up a machine. If the specs list a motor at 1hp at 120/220V does that mean you can wire it up to a 220V outlet? If not why do company list their motor is such fashion? Just wondering. :confused:

Thanks for the help.

Brian

[Jim DeLaney]

It means that the motor is capable of running on either 11/ or 220 volts, BUT there are significant wiring changes that have to be made within the motor to change from one to the other.

Most motors have a wiring diagram, either as part of the nameplate, or under the cover where the power wire goes into the motor, showing which connections need to be made for the different voltages.

Failure to connect the leads properly can lead to damages - both to the motor, and to the person plugging it in! If you're unsure of how to wire it up properly, HIRE AN ELECTRICIAN!

[Rob Russell]

Hello all,
Question for you about wiring up a machine. If the specs list a motor at 1hp at 120/220V does that mean you can wire it up to a 220V outlet? If not why do company list their motor is such fashion? Just wondering. :confused:

Thanks for the help.

Brian

Brian,

The short answer to your question is that, Yes - the machine can be run on a 220v line.

The longer answer is how.

To convert to motor from 120v to 240v wiring, you need to remove the cover plate on the motor and change the wiring connections inside. There will be a diagram either on the motor's data plate or inside the cover that shows what the 120v vs. 240v connections are. You also need to put a different plug on the end of the cord for the machine and you should reidentify the white conductor as hot.

Why would you do this? A motor that draws 15 amps @ 120v draws 7.5 amps per leg @ 240v. It's still using the same amount of electricity, but the current draw is cut in half because it's split over 2 legs. If you have long runs from the breaker panel to the outlet, you'll get less voltage drop over 2 legs than over 1.

One myth is that motors "make more power" on 240v vs. 120v and that's a lot of bunk. The motor doesn't know how you wired it. Either way your electric meter will show the same number of watts consumed. You will see a 240v motor startup faster because it's got 2 legs to draw startup current from - jumping to life rather than r-rr-rrr-rrrrrrr'g up to speed.

Rob

[Jason Roehl]

One myth is that motors "make more power" on 240v vs. 120v and that's a lot of bunk. The motor doesn't know how you wired it. Either way your electric meter will show the same number of watts consumed. You will see a 240v motor startup faster because it's got 2 legs to draw startup current from - jumping to life rather than r-rr-rrr-rrrrrrr'g up to speed.

Rob
Not entirely bunk, just not practically seen in real-world use. More amps => more heat => more resistance => more voltage drop in the wiring => more amps in the motor windings => more heat in the motor => lower service life...

But the difference is probably only measurable with specialized equipment. Who knows? Over the life of the tool, you might save a kWh or two using it at 240V instead of 120V, and it might last a little longer. There's a reason the power company doesn't transmit power across the country at 120V--more like 120kV--less loss.

[Chris Padilla]

Guys, just look at this as a power or energy thing. It doesn't change, period. Energy release in the form of heat doesn't change regardless of the voltage...the power/energy is the same. You can't have current without voltage and neither one is a measure of heat or energy.

[jim barter]

Brian / Wiring a motor to 240 volts compared to 120 is the best option for something like a tablesaw or air compressor.The main reason is the voltage drop.When using your tablesaw and you bog it down it can recover faster with 240 .A 3 % voltage drop is the max allowed on a branch circuit.As the other guys were saying the same amount of watts is consumed at 120 or 240.No saving on the power bill but a better working tool.
Jim

[Brian Walter]

Not entirely bunk, just not practically seen in real-world use. More amps => more heat => more resistance => more voltage drop in the wiring => more amps in the motor windings => more heat in the motor => lower service life...Jason,

I'm not sure if I'm interpreting what you are saying correctly or not, but if you are saying that when running the motor on 120v that there will be more amps in the motor windings, you are mistaken. The voltage drop and current flow through each winding is the same whether running on 120v or 240v. For example, a motor that draws 15 amps when running on 120v, has 7.5 amps through each winding. This is because the motor windings are in parallel, with each winding carrying 1/2 the total current. The same motor wired for 240v will draw 7.5 amps and because the windings are now in series, each winding must carry the entire current. If you think of the motor windings as resistors and draw out the circuits, it is easier to visualize. When wired for 120v the reistors are in parallel and when wired for 240v they are in series.

If I misinterpreted what you were saying, I appologize. But this clarification may help others.

Brian Walter

[Jason Roehl]

Brian, I was just talking really about the voltage drop in the wiring TO the motor causing a higher amp draw, leading to more heat in the motor. In the example you laid out, it may be 7.50A @ 240.0V, or 15.01A @ 119.9V. My point was that it is negligible, but there. Most NEMA motors now (that I've seen) are rated at 115/230V anyway, while many people see 120+V on a leg in their house current. Like I said, "just not practically seen in real-world use." Power companies have lower line losses at higher voltages--higher voltage means lower amps to transmit the same power. Higher amperage would mean either much larger wiring, or much greater loss to heat (from high amperage being pushed through small wiring--like an electric stove) The 120/240V wiring debate on a small motor is the same thing, only on a MUCH, MUCH, MUCH smaller scale, to the point of being negligible, or very, very close to it.

Otherwise, good clarification.

[Jim Becker]

Just to make this even more interesting...the motor windings are still seeing only 120v internally when you set up a "dual voltage" motor for 240v operation. :D

[Mike Cutler]

Brian. Small motors can be classified in a few different manners.A motor that has a 110/220 rating is a dual use motor and the manufacturer is stating that the motor can be used in either voltage application, and has theoretically been tested in either application. It will most likely have a UL stamp of approval. This motor will require some wiring modifications to be used correctly with each application. Small motors also come rated as specific 110 or 220 applications only.
The manufacturer of the motor does not know the specific application that an equipment manufacture may intend for the motor.
"Rule Of Thumb For Small Motors" ( And we all know what happens to thumbs that stick out there!)
1HP=746 watts.
HP=IxVxPFxEFF/746,where PF( Power Factor)=.86 and EFF ( Motor Efficiency)=.81. Using this formula current can be calculated as follows for a 1HP single phase motor.
I=HPx746/(VxPFxEFF) or,
I=1X746/ (120 x.86x.81) or,
I=8.9 amps.
Current for the same Motor connected to 240 would be.
I=1x746/ (240x.86x.81) or,
I=4.46 Amps.
The use of 110 or 220 in this application would really be up to the individual consumer, as either voltage is capable of power this motor sufficiently. An esoteric argument can be made for the longevity/reliability of the individual conductor, in which 220 would give longer life in theory, but the practical application is moot.
Chris stated that neither current nor voltage is an indicator of power or heat. This statement while true, needs to be carried a few steps further. Current and voltage are units that make up power as measured in watts. Watts is an energy measurement and has a direct thermal correlation. Conductors are rated in their ampacity, however part of that rating also includes the ability of the conductor itself as well as the insulating jacket and substrate materials to dissipate heat, or watts.
The actual answer to your original question is that, yes, this motor can be used safely and properly in a 220 application with the proper wiring convention. Too much free time here at work Sorry for being long winded.

[Brian Triplett]

I have a new 6” jointer and I was just wondering if it was worth changing the plug and the wiring on the motor to go to a 220V outlet. I already have the outlet wired (I actually planned for the future :eek: ) Thanks for all the input. Looks like I will go adhead and wire it up of the 220V outlet. I mean why not?

Brian

[Chris Padilla]

Brian, go for it...wire it up to 240 V (really, there isn't any 220 or 230 or 250...did I just start another thread? :) ). The plugs tend to be more expensive for 240 V applications (especially twist-locks although I like them the most).

[William Hall]

One advantage for using 240V is to help balance the amperage draw across both legs. You don't dim the lights as badly when you turn on your table saw.

[Chris Padilla]

Well, you shouldn't have the TS on the same circuit as your lights! :)

[William Hall]

Well I guess I should have said... the lights in the rest of the house since my basement shop shares a service panel with the rest of the house;) The lights in my shop are definately on separate circuits!!!

William

[Byron Trantham]

Let's see now; what was the question? :D

[Brian Walter]

Brian, the only reasons I can see for not wiring the motor for 220v is the extra cost for the outlet and plug and that you may have less outlets to plug it into, which if you want to move the machine around and use it in different locations, may be an issue.

Brian Walter

[Rob Russell]

I have a new 6” jointer and I was just wondering if it was worth changing the plug and the wiring on the motor to go to a 220V outlet. I already have the outlet wired (I actually planned for the future :eek: ) Thanks for all the input. Looks like I will go adhead and wire it up of the 220V outlet. I mean why not?

Brian

I do agree with running machines on 240v, if only that the startup current draw is split over the 2 busses in your panel instead of drawing from only 1.

I'd recommend picking a twisk-lock plug/receptacle configuration and sticking with that for your shop. In the future, as you add machines, you just need to replug the machine and use the existing receptacles. If your shop is such that you need to move machines around, this will make your life easier. I'd go with the NEMA L14-20 plug configuration. It's a 3-pole, 4-wire, grounding config - which means that it has 2 hots, a ground and equipment grounding conductor. From that 1 plug you can run 240v or 120v loads. If you have a machine that has both (240v table saw with built-in router table), you can install a j-box on your saw and create a 120v receptacle from that. For machines that are pure 240, you just don't use the neutral pin on the plug.

JMO - YMMV.

Rob

[Jim Becker]

I do agree with running machines on 240v, if only that the startup current draw is split over the 2 busses in your panel instead of drawing from only 1.
Rob, I was always under the impression that a double pole breaker would always be on both busses. When would it not? And why would it work if only one buss was involved...wouldn't the two legs be on the same phase?:confused:

[Carl Eyman]

There Have been a lot of high powered answers to this post, but you need only one. WIRE IT 240 - IT WORKS BETTER. DAMHIKT

[Rob Russell]

Rob, I was always under the impression that a double pole breaker would always be on both busses. When would it not? And why would it work if only one buss was involved...wouldn't the two legs be on the same phase?:confused:

Wiring the machine for 240v draws from both busses; wiring for 120v only draws from one. I know that you know that. Apparently I just wasn't clear in the way that I wrote it.

There is a case where a 2-pole breaker draws from 1 buss - when it's a 1/2 size breaker. If someone tried to use one of those, it wouldn't work too well.

Part of this gets into defining what a "pole" on a breaker is. Does it mean the number of circuits you can run from it or the number of busses it attaches to? "Pole" isn't an NEC-defined term, so I'd guess it's open to varying interpretation (not that the NEC itself doesn't have all sorts of things open to intrepretation ...). I think most people look at "pole" and equate it to the number of circuits.

[Chris Padilla]

I do agree with running machines on 240v, if only that the startup current draw is split over the 2 busses in your panel instead of drawing from only 1.

I'd recommend picking a twisk-lock plug/receptacle configuration and sticking with that for your shop. In the future, as you add machines, you just need to replug the machine and use the existing receptacles. If your shop is such that you need to move machines around, this will make your life easier. I'd go with the NEMA L14-20 plug configuration. It's a 3-pole, 4-wire, grounding config - which means that it has 2 hots, a ground and equipment grounding conductor. From that 1 plug you can run 240v or 120v loads. If you have a machine that has both (240v table saw with built-in router table), you can install a j-box on your saw and create a 120v receptacle from that. For machines that are pure 240, you just don't use the neutral pin on the plug.

JMO - YMMV.

Rob
Rob,

I'm not sure I agree with this nor do I think it is a good idea HOWEVER, your idea depends on the breaker installed on this circuit. All of my 240 V motors require a 30 A breaker. If I wired off a 120 V application from this breaker, it could be dangerous if that application is only designed for 15 A or maybe 20 A. Am I following correctly what you state above or did I miss something as usual?

[Rob Russell]

Rob,

I'm not sure I agree with this nor do I think it is a good idea HOWEVER, your idea depends on the breaker installed on this circuit. All of my 240 V motors require a 30 A breaker. If I wired off a 120 V application from this breaker, it could be dangerous if that application is only designed for 15 A or maybe 20 A. Am I following correctly what you state above or did I miss something as usual?

Chris,

In your situation, it wouldn't be a good idea (would violate the NEC to put a 15/20 amp general use receptacle on a 30-amp circuit).

For the majority of folks who have 15 or 20 amp circuits, this technique works just fine and is acceptable under the NEC.

Rob

[Jim Becker]

There is a case where a 2-pole breaker draws from 1 buss - when it's a 1/2 size breaker. If someone tried to use one of those, it wouldn't work too well..
I hadn't considered the "two pole off of one buss" as clearly because when I had to use this kind of thing for 240v circuits before the 200 amp upgrade to the shop, my compact breakers were quads that dealt with the issue correctly, unlike a double that takes one space and is designed for two 120v circuits on one buss, not a 240v hookup. But human nature being what it is, I can imagine someone trying to make it work!

Terminology can be fun. In my business (telecommunications) the marrying of the traditional voice world with the data networking world is making for some very interesting confusion where the same acronyms mean remarkably different things to each group! It's a challenge to talk to both sets of folks at the same time...and have them get the same message.

[Howard Acheson]

All convertable 120/240 motors run on 120 volts internally. There are two coils each running 120 volts and using 1/2 the 120 volt amperage (The coils act as a resistance and split the amperage). All you do when you re-wire the motor to run on 240 is change the wiring connecting of the coils from parallel to series. When wired for 240 volt operation, one 120 volt leg and its associated amperage is routed to each individual coil rather than a single 120 volt line providing 120 volts to both coils. The same voltage and amperage runs through the individual coils no matter how it it wired. It is amperage that creates heat, and because the amperage in each coil is the same for both wiring configuations, there is no difference in the heat produced by either wiring configuation. The motor is perfectly happy with either voltage and doesn't even know you made the change.

[jim barter]

Rob/ When calculating motor overcurrent devices(fuses or breakers) you have to allow a min of 1.25% of the full load amps(fla).In the case of motor loads the overcurrent device can and most times will be larger than the receptacle or for that matter conductor.The thermal overload in the motor protects the conductor and the motor while the overcurrent device protects the entire circuit.A 30 amp fuse or breaker will trip on a short circuit as quickly as a 15 amp.The overcurrent device has to be sized properly in order to allow the inrush currents required to start a rotating magnetic field to make the motor turn.You are allowed to increase the overcurrent device up to 300 % of the fla if the calculated size does not allow the motor to start.Sometimes this will happen to a motor that starts under load,unlike say a fan or table saw .The device say a receptacle is allowed to have in the case of a 20 amp ,a 20 amp load.Just remember that no overcurrent device feeding branch circuits can be loaded greater than 80 % of its rating otherwise premature tripping can occur due to heat.
Jim

[Rob Russell]

Jim,

What you're describing is a synopsis of the calculations in Article 430 - Motors, etc. I've been through that section many times to make sure my home-built rotary phase convertor met the NEC.

For most residential workshops and machines, typical branch-circuit wiring is enough. IOW, the short circuit and ground fault protection is the same as any motor overload protection and is simply the circuit breaker. I do understand your point. For most people, it's simply not necessary to go to the lengths of those calculations.

Given that premise, my point to Brian's original question was a suggestion that maximizes flexibility in wiring his workshop. 20-amp rated, 4-wire, 3-pole twist lock plugs/receptacles are adequate for 99% of the workshops out there. When you're running 7.5HP motors, that may be a different story - but my stuf is 3-phase. Ironically, my motors will draw less current at 3-phase than a 5HP single phase motor.

Rob

[Jim Becker]

20-amp rated, 4-wire, 3-pole twist lock plugs/receptacles are adequate for 99% of the workshops out there.
I'm curious as to the reason for the 4-wire/3-pole connections when our 240v tools (sans the big, burly 3-phase stuff that some use) only require 2 poles and a ground? All my 20 amp 240v circuits use L6-20 twist locks and my 30 amp circuit for the FS350 uses the 30 amp version of the same. (slightly larger is the only noticable difference) 'Just trying to understand what you are suggesting, Rob.

[Rob Russell]

I'm curious as to the reason for the 4-wire/3-pole connections when our 240v tools (sans the big, burly 3-phase stuff that some use) only require 2 poles and a ground? All my 20 amp 240v circuits use L6-20 twist locks and my 30 amp circuit for the FS350 uses the 30 amp version of the same. (slightly larger is the only noticable difference) 'Just trying to understand what you are suggesting, Rob.

Jim,

As I put in an earlier post in the thread




... From that 1 plug you can run 240v or 120v loads. If you have a machine that has both (240v table saw with built-in router table), you can install a j-box on your saw and create a 120v receptacle from that. ...]



I can think of a number of examples where you'd have a 240v machine with a 120v accessory.

240v table saw with a 120v router table built into it.
240v bandsaw with a 120v clip-on or magnetic base work light.
240v shaper with 120v power feeder


By running a 3-pole, 4-wire configuration, you give yourself the flexibility to plug in a machine you want both types of power. Granted, you need to do some wiring on the machine to pull off both 240v and 120, but that's a simple junction box on the machine. Your cord and plug go to the j-box, short 240v cord feeds the actual machine and your 120v feed goes to wherever you need it - which could just be a receptacle in that j-box.

Make myself clearer or am I still managing to confuse the issue?. FYI, I won't be able to respond until tomorrow night - just in at work to pick something up and saw your question.

Rob

[Jim Becker]

Sorry, Rob...I apparently missed that previous post. That makes perfect sense. Thanks for reiterating!