120 to 220 bandsaw conversion?

[Ken Casser]

Okay, I searched and searched, but couldn't find what I need.

I just picked up a Delta 28-203 14" bandsaw, 3/4 horse Marathon motor, and would like to convert it to 220. I read the label, but it doesn't match up with the wires in the box. Any advice? I have four wire nuts inside the box. Black to Black, White to White or Yellow(I can't tell which), Orange, Red, Yellow & White in wire nut #3, and Orange, Red, Blue & Black in wire nut #4. I have a meter if that helps, but I don't know what to check with it. Thank you for helping!

[Ken Fitzgerald]

Ken,

I went to the Delta Website. They don't show an electrical schematic. Do you have a manual? Read the tag on the motor. It may not be capable of being operated at 220vac.

[Mike Henderson]

If it's dual voltage, the coils will be colored as follows: (if your motor is standard)

Coil 1 - blue and white.
Coil 2 - orange and yellow
Starting coil - red and black

For low voltage, all the coils are in parallel.

For high voltage, coil 1 and coil 2 are in series. The starting coil is put across either of the coils. To reverse the motor, reverse the starting coil connections.

If you're going to check the coils with your ohm meter, note that the starting coil has a capacitor in series with it.

Mike

[Ken Casser]

Ken, my owners manual doesn't go into any detail on the motor. The tag on the motor says 115/230, and there is writing that says to wire it one way for 'low voltage' and another way for 'high voltage', but the choices don't match up with what I'm seeing. I can get that information tonight if it would help.

Mike, thank you, your information probably would help, but I don't know enough about 'coils' to know what this means, and I don't know what having a capacitor in there tells me. I also don't know what to do to change something from parallel to series in this instance. I know just enough to get in trouble, but not enough to get myself back out. It confuses me that the two sets of four wires each have an Orange and a Red, but I'm suspecting that I would leave those alone and just change the Yellow/White and Blue/Black, but don't know the proper way to do it.

Thank you both for your help.

Ken

[Howard Acheson]

Let me ask a basic question. Why do you want to change the voltage? The motor will produce exactly the same power, and run exactly the same, no matter which way it is wired. If it's running fine now there is no reason to change it.

[Ken Casser]

Good question. I always thought 230 would give it more power, smoother performance, lower amps, etc. And, I'm concerned that if I plug the saw and my vac into the same outlet, it might overload the circuit whereas I have 220 available right next to my 120. At the guy's house who I bought it from, his lights would go dim out when he turned on the saw. I'll look a little further before deciding, and thank you for the advice.:)

[Rick Christopherson]

Let me ask a basic question. Why do you want to change the voltage? The motor will produce exactly the same power, and run exactly the same, no matter which way it is wired. If it's running fine now there is no reason to change it.......and more importantly, a 3/4 hp motor is not a good candidate for the argument that it needs to be done due to substandard wiring. A 120 volt 3/4 hp motor is going to draw only about 7 amps at maximum rated load.

[Ken Casser]

Thanks, Rick, I'll check again when I get home, but I thought it said something like 16 amps at 120. I have some homework to do, but I have plenty to do with this saw before the wiring is going to bother me. I just thought that while I have the saw off the base and the motor is easy to get to, I may as well do the conversion. As always, I read too much. :D or, not enough...:D:D

[Chris Konikowski]

Let me ask a basic question. Why do you want to change the voltage? The motor will produce exactly the same power, and run exactly the same, no matter which way it is wired. If it's running fine now there is no reason to change it.

Less amperage draw, less heat, longer lasting motor....

[Tom Veatch]

Less amperage draw, less heat, longer lasting motor....

Less amperage draw: Correct as far as the service to the motor is concerned.

Less Heat: Indeterminate. If the service wiring is such that voltage drop in the low voltage configuration causes a significantly longer start transient, then more heat could be generated internally during startup than would be generated in the higher voltage configuration. But that's a transient, short-lived condition. During normal operation with adequate service and nominal voltages, the same amperage flows in the internal coils in either case. Assuming nominal voltages, same power consumption during normal operation = same heat generation.

Longer lasting motor: Indeterminate. Internally, the motor doesn't know the difference between running with the high voltage (240) connections and running with the low voltage (120) connection. Assuming nominal voltages, either configuragion produces the same voltage drop across and current through the individual coils.

The only advantage to the motor of running the high voltage configuration is if the supply wiring is marginal. If the higher service amperage at the low voltage produces a significant voltage drop in the service wiring there would be advantage to using the high voltage setting. Otherwise, the motor really doesn't see any difference.

[Tom Veatch]

...16 amps at 120. ...

That power consumption (1.9 KVA) sounds more like a 2HP motor than it does a 3/4HP motor. If that is the correct amperage draw of the motor, and you have 240v service readily available, IMO, there would be no downside to converting.

[Ken Casser]

That's what I was thinking - I have the service, it should be a simple thing to change the wires - I've done it before on my DC, and I didn't know of any reason not to do it. But I will check the stated amperage draw just to be sure. Now, if only I could figure out which wires go to which...:D Of course, if I can't, I'll leave it alone.

[george wilson]

One piece of advice: Chinese motors often have completely BOGUS wiring diagrams. I don't know why,but they most certainly can be false. I've had exactly that problem converting a milling machine to 220. I hired an electrician. He was baffled. Just had to keep making random combos of the wiring until it worked. Just poor quality control? Untrained factory workers? Possibly.

[Ken Casser]

I'll have to check to see if it is Chinese. It was made in '92, and the saw has a Made In USA sticker, but I don't know when we started buying everything from China.

[Rick Thom]

If Ken does convert the motor to 220, is the existing 110 on/off switch going to also require replacement?

[Ken Casser]

Tom, it's actually 11.4/5.7 amps. I had it wrong.

George, the motor says Made In The USA. It has the Delta name on it, and in smaller print it says that it was made by Marathon.

I'll play with it later to see what wires go to what. Maybe that will help me.

[Ken Casser]

Okay, I think I've figured it out. I'll be plugging it in in about half an hour. If you don't hear from me again, I'll be at the Emergency Room. :eek::eek::eek:

[Tom Veatch]

If Ken does convert the motor to 220, is the existing 110 on/off switch going to also require replacement?

Probably not. Since the tool is designed for dual voltage, the switch may already be a double pole (DP) switch. As a general rule, I use a DP switch on a 240v load so that both hot wires are dead at the load when the switch is off. But that's not a functional requirement. It may be required for UL listing, I don't know. As far as the power rating of the switch is concerned, if it's rated for the motor HP at 120 volts, typically it will also be rated to handle the power at 240 volts. That's assuming the switch is rated for the higher voltage which, again, it probably is.

A single pole (SP) switch on one of the hot leads will break the circuit and control the motor just as well as a DP switch. But, with an SP switch, one of the leads at the load will be hot even if the switch is turned off. But, you ALWAYS unplug the tool before messing around with the electrics, don't you!!! If you don't, be sure you don't miss any premiums on your insurance policies.;)

[Rick Moyer]

Okay, I think I've figured it out. I'll be plugging it in in about half an hour. If you don't hear from me again, I'll be at the Emergency Room. :eek::eek::eek:

Well, it's been about twelve hours, hope Ken's sleeping or sawing, but not in the emergency room!:eek:

[Mike Lipke]

Less amps, true.
Voltage though is double.

amps X volts = watts

Same wattage is going thru that motor, so you are using just as much electricity, either 110 or 220. With same wattage being consumed, I think the heat produced is the same.

A big advantage of 220 volt motors is you can run double the amps thru the wires servicing the tool.
For example, 14 gauge wire at 110 volts will only run 15 amps, or 1650 watts.

14 gauge wire at 220 volts will allow you to run 15 amps as well, but deliver 3300 watts.

[Rod Sheridan]

Less amps, true.
Voltage though is double.

amps X volts = watts

Same wattage is going thru that motor, so you are using just as much electricity, either 110 or 220. With same wattage being consumed, I think the heat produced is the same.

A big advantage of 220 volt motors is you can run double the amps thru the wires servicing the tool.
For example, 14 gauge wire at 110 volts will only run 15 amps, or 1650 watts.

14 gauge wire at 220 volts will allow you to run 15 amps as well, but deliver 3300 watts.

Mike, the current carrying capacity of a conductor is not affected by the voltage.

14 AWG wire is rated at 15 amperes, it doesn't change from 120 volts to 240 volts.


Regards, Rod.

[Roger Frazee]

As the saying goes... ' I hope he didn't let the smoke out of his motor...:)'

[Jim Solomon]

If Ken does convert the motor to 220, is the existing 110 on/off switch going to also require replacement?

Nope :D The amp draw would be less than the 110V setup. Maybe you where thinking of 3 phase as opposed to single phase?

[Chris Padilla]

In regards to the switch for 120 V vs 240 V. It is a matter if both legs of the 240 V need to be disconnected. For 120 V, only one leg is hot. Certainly, disconnecting one leg will stop the current but the other leg is still hot.

For safety, I believe both hot legs for 240 V should be disconnected so a double-pole switch should be used.

[Roger Frazee]

Mike, the current carrying capacity of a conductor is not affected by the voltage.

14 AWG wire is rated at 15 amperes, it doesn't change from 120 volts to 240 volts.


Regards, Rod.


Actually 14 awg is rated 20 amps unless being derated in conduit but it must be protected at 15 amps for most installations... there are a few exceptions...;) Please don't take offense Rod...I'm only trying to clarify...I haven't been to good at that lately....:)

[Chris Padilla]

Less amps, true.
Voltage though is double.

amps X volts = watts

Same wattage is going thru that motor, so you are using just as much electricity, either 110 or 220. With same wattage being consumed, I think the heat produced is the same.

A big advantage of 220 volt motors is you can run double the amps thru the wires servicing the tool.
For example, 14 gauge wire at 110 volts will only run 15 amps, or 1650 watts.

14 gauge wire at 220 volts will allow you to run 15 amps as well, but deliver 3300 watts.

Actually, and has been said here, the motor could care less what the voltage beling delivered to it is since the coils are wired appropriately. Nothing in the motor changes.

Only the current being DELIVERED to the motor changes when going from 120 V to 240 V--it is half as much at 240 V. So this conversion is usually only beneficial to the wiring in the wall. At the higher delivered voltage, with the lower current, less voltage will be dropped across the resistance of the wiring in the wall.

Some claim a peppier starting motor on 240 V vs 120 V. I think this is because more voltage is available (more current available) and less is being wasted in the wiring upon start up. Start up is key here...once the motor reaches a steady-state, it is no different than if it were on a 120 V circuit (except there is less current in the wires in the wall...less current means less heating up of the wires in the wall....)

[Roger Frazee]

How about this....a 2 hp motor stays 2hp and it doesn't matter what you do to it as far as voltage is concerned....:)

[Tom Veatch]

Actually, and has been said here, the motor could care less what the voltage beling delivered to it is since the coils are wired appropriately. Nothing in the motor changes.

Only the current being DELIVERED to the motor changes when going from 120 V to 240 V--it is half as much at 240 V. So this conversion is usually only beneficial to the wiring in the wall. At the higher delivered voltage, with the lower current, less voltage will be dropped across the resistance of the wiring in the wall.

Some claim a peppier starting motor on 240 V vs 120 V. I think this is because more voltage is available (more current available) and less is being wasted in the wiring upon start up. Start up is key here...once the motor reaches a steady-state, it is no different than if it were on a 120 V circuit (except there is less current in the wires in the wall...less current means less heating up of the wires in the wall....)


Chris, I've heard it said that the measure of a man's intelligence is how closely he agrees with you. Based on that measure, you're a pretty smart guy.:D

I generally avoid "Me, too!" posts, but about the only thing that I can add is that 240 vs 120 benefits, such as they are, will usually only be noticable under high current conditions. You mentioned startup which is the major event in that category, but you might see some benefit, although there's no guarantee, from it being a little more difficult to stall the motor under load. It all depends on the ability of the supply wiring to provide full voltage at the motor under high current conditions.

[Mike Henderson]

In regards to the switch for 120 V vs 240 V. It is a matter if both legs of the 240 V need to be disconnected. For 120 V, only one leg is hot. Certainly, disconnecting one leg will stop the current but the other leg is still hot.

For safety, I believe both hot legs for 240 V should be disconnected so a double-pole switch should be used.
Amen, Brother.

I'd never put a single pole switch on a 240V tool. One day, you'll forget to unplug the tool before you work on it. Or you'll sell it and the person who bought it will think it has a two pole switch.

Mike

[Ken Casser]

Thanks! Yup, it works great. There are other issues with this saw, but I'll leave them to another post. Thank you all for your help.:):)

[Rick Christopherson]

In regards to the switch for 120 V vs 240 V. It is a matter if both legs of the 240 V need to be disconnected. For 120 V, only one leg is hot. Certainly, disconnecting one leg will stop the current but the other leg is still hot.

For safety, I believe both hot legs for 240 V should be disconnected so a double-pole switch should be used.Amen, Brother.

I'd never put a single pole switch on a 240V tool. One day, you'll forget to unplug the tool before you work on it. Or you'll sell it and the person who bought it will think it has a two pole switch.

MikeWhat happens if you forget to unplug the tool before working on the switch? Both conductors on the upstream side of the switch are hot. There is obviously nothing wrong with opening both conductors, but I have always felt this was a poor reason to worry about it, because there will always be live conductors present in virtually every system once you open a secured cover without disabling power. The neutral is still a current carrying conductor too. Anyone foolish enough to open the peckerhead of a motor without cutting power deserves to have his widow selling his tools to the rest of us on eBay. :D

I am not saying it is a bad idea or anything, but simply that people should be told that it is their option if they want to replace a single-pole switch with a double-pole switch when they make this conversion. It is not mandatory that they use a 2-pole switch on a 240 volt motor. (I just read this within the last 24 hours, but I cannot remember which article, but I am sure it was within NEC 430.)

Oh, I found it!

Article 430.84 Need Not Open All Conductors. The controller shall not be required to open all conductors to the motor.
Exception: Where the controller serves also as a disconnecting means, it shall open all ungrounded conductors to the motor as provided in 430.111.

[Mike Henderson]

Rick - you and I have had this discussion before. You're right, there's no code requirement to break both hot connectors but I prefer to do so on my equipment. I'll also recommend it to anyone who asks me.

We may disagree on this, but I feel it's safer to have a switch that breaks all the hot lines.

Mike

[Mike Lipke]

Mike, the current carrying capacity of a conductor is not affected by the voltage.

14 AWG wire is rated at 15 amperes, it doesn't change from 120 volts to 240 volts.


Regards, Rod.

You are correct. I meant to say wattage doubles when you go to 220 volts. As I did say, correctly, that 14 g wire carries 15 amps, by code, whether 110 or 220 volts.

[Rick Christopherson]

No Mike, we don't actually disagree. I just feel that it is important that people know what their options are so that they can make that choice for themselves, especially when specific circumstances favor one over the other.

The standard advice gets repeated so much that most people do not know that it is their choice to make, and I am simply balancing that advice.

[Mike Henderson]

No Mike, we don't actually disagree. I just feel that it is important that people know what their options are so that they can make that choice for themselves, especially when specific circumstances favor one over the other.

The standard advice gets repeated so much that most people do not know that it is their choice to make, and I am simply balancing that advice.
I understand and appreciate your knowledge and advice.

One thing I remind people of occasionally is that "code" is actually the minimum acceptable. It's okay (and may be desirable) to exceed code in certain situations.

Mike

[Tom Veatch]

...
Article 430.84 Need Not Open All Conductors. The controller shall not be required to open all conductors to the motor....

I'd never put a single pole switch on a 240V tool. ...

I've got a question, and I'm not sure how to ask it without ruffling somebody's feathers which I've no intent to do.

Rick says, and cites the NEC to the effect, and Mike agrees, that there is no code requirement for a DP switch on a 240v (two hot wires) motor. But, my question is, "Is the NEC even applicable?"

The original discussion involved a bandsaw being converted from 120 to 240 volts and the question was asked whether the switch would need to be replaced also. There's no question that the NEC, or at least the local jurisdiction's implementation of the NEC, is applicable to the permanent wiring up to, and including, the wall socket. But the bandsaw in question is a "plug and cord" device, not permanently hardwired into the circuit.

So, do code requirements extend past the wall socket into the device plugged into that socket? If it does, how are they enforced? You're certainly not required or expected to pull a permit and schedule a visit by the electrical inspector to plug something into the wall socket in your living room.

Or do the provisions and requirements of the electrical code stop at the permanently wired receptacle? If so, what rules apply to the "plug and cord" device that's plugged into that receptacle? UL listing? If that's the case, maybe the UL listing requirement, if any, that addresses switching 240v devices is more appropriate to the switch question.

The reader is, of course, free to do it however they wish, but I'll continue to use DP switches on 240v loads, either permanent wiring or plug and cord devices, not because of any regulatory requirement, but simply because I'm more comfortable doing it that way.

[Rick Christopherson]

That's a good question Tom, and I am not entirely sure what the answer should be. However, it actually becomes a moot point, because if the NEC doesn't apply, then nothing applies.

UL is not a regulating body and adherence to their requirements is voluntary only if the manufacturer (not the end user) wishes to have the UL label affixed to their product. For example, you will notice than none of the Fein Turbo vacuums have a UL sticker. This is not because they are dangerous, but because a specific UL requirement that does not serve the needs of the end user prevents Fein from obtaining a UL listing for the vac (without great inconvenience to the end user).

UL987 section 19.3 does in fact stipulate that.....oh jeez, do they use crappy wording....if the tool is over 125 volts, then it should have a 2-pole switch (it makes no mention of opening all ungrounded conductors, which is the proper wording for such a directive :mad:).

Anyone that has spent any time reading UL documents knows that they are pretty rediculous. Did you know that the majority of the poor english and typographical errors in owner's manuals were actually mandated by UL 60745? I kid you not! :confused: UL 60745 paragraph 8.12.1 states that manuals must contain the safety warnings listed in the subsequent sections, and they "must be verbatim!" Those safety warnings that everyone laughs at were riddled with mistakes and typos that every manufacturer was forced to follow. Only recently did many of these errors get fixed, but there are still a few.

As for the NEC's applicability to this discussion, you can't have it both ways. Either they are or they are not, and there have been many discussions where people (including yourself I believe) that have used the NEC's statements to corroborate information provided on the forum. In this particular case, the NEC states what most people familiar with electrical systems already know--it takes only one break in a circuit to stop the flow.

[Rod Sheridan]

I would like to see a 2 pole switch on 240 volt equipment to disconnect both lines, however as Rick indicated, it's not required.

The one item that hasn't been adressed is that if you only open one line with a single pole switch, the switch will see 240 volts across the open contact, not share the voltage across two open contacts as would happen with a 2P switch.

You would have to check whether the single pole switch is actually rated for 240 volts or not.

Regards, Rod.

P.S. As many have stated, I wouldn't change a 3/4 HP motor to 240V unless as in this case, the person doesn't have enough 120 V circuits to run his vacuum and motor at the same time.

[Rick Christopherson]

I am sorry Rod, but that is a little misleading. It makes no difference whether it is a single pole switch or a double pole switch, it must be rated for the voltage. Because it is virtually impossible for both contacts to make the connection at the same instant in time, one of the two contacts will see the full circuit voltage. They do not necessarily share or split this voltage.

[Roger Frazee]

HI Tom

That is.... a very good question.... and I'm not sure one will ever get consensus on the correct answer.

I think it my be hidden in Article 90 Specifically 90.2 (A) and (B). I'm reasonably sure that for residential or commercial the authority ends at the connection to the supply conductors (utility). As an example if your home has and overhead messenger utility supply to your mast. The NEC would take over where the drip loop of the entrance conductors connect to the overhead supply from the utility. The utility falls under regulation by the NESC.

But that wasn't your question but it gives us a beginning point at least....:D

Now I think the defintion of branch circuit conductors gets us close to the end for a dwellings premise wiring and associated devices and equipment (Panels etc).

I may not get it perfect but I believe this is pretty close " Branch circuit conductors are those conductors between the Final overcurrent device and the outlet or connected load." So I think that covers the end of NEC regulation as to branch circuits and associated equipment of the premise wiring.

Then of course there are feeders etc.. but trying to summarize I would say the NEC goes from the connection point of the supply and to the connection point of a load or outlet for a load.

Now that seems easy but I don't think it is quite that easy. The NEC spends a lot of ink in several chapters identifing specific loads like motors, motor operated appliances and so on... and how conductors and cords and plugs must be rated in order to connect to the premise distribution outlets and conductors like branch circuits depending of course their intended use for the connection point....is the plug going to be a disconnect.

So it would seem to me the NEC regulates up the connection to the utilization equipment whether that be a plug and cord or hardwire.

If a switch is used for on and off on a piece of equipment that is cord and plug like a table saw IMO does not fall under the NEC. It has already been wired into the tool by the manufacturer. The nec is not a design enforcer. But the manufacturer has his set of rules... And I believe they would have to work to a degree with the NEC and listing laboratories to have some sort of consensus on the minimums required for control and disconnection of any piece of equipment so that an electrician can bring power to the load in compliance with code.... and be able to install the necessary conductors and overload and circuit protection required for safe operation that protects the utilization equipment and for human safety. So I would say it is a hand in hand deal as Rick said with the manufacturers and the NEC and the listing laboratories. But if you have to replace a switch on a saw or an electrical component on a saw I don't think the NEC necessarily regulates how you should wire it but only sets the minimums of how it should be wired.

Just my thoughts

[Rod Sheridan]

I am sorry Rod, but that is a little misleading. It makes no difference whether it is a single pole switch or a double pole switch, it must be rated for the voltage. Because it is virtually impossible for both contacts to make the connection at the same instant in time, one of the two contacts will see the full circuit voltage. They do not necessarily share or split this voltage.

Yes Rick, I did not mean to indicate that the switch didn't need to be rated for the voltage, that was my point regarding checking the switch voltage. I'd hate to see the person use the wrong switch......regards.....Rod.

[Roger Frazee]

Yes Rick, I did not mean to indicate that the switch didn't need to be rated for the voltage, that was my point regarding checking the switch voltage. I'd hate to see the person use the wrong switch......regards.....Rod.

You didn't Rod you were very clear about the switch rating needing to be 240 volts.

However on a 240 volt switch I suppose you won't see full voltage on the contact(s) until they close...You need to be very careful about those nanoseconds between contact closures....:)

But I certainly don't see anything wrong with your sharing analysis. A double pole switch would share the opposite leg voltages in the open position over 2 contacts ...a single pole the opposite leg voltages over one.
I think it is fine to look at it that way.

[Roger Frazee]

......and more importantly, a 3/4 hp motor is not a good candidate for the argument that it needs to be done due to substandard wiring. A 120 volt 3/4 hp motor is going to draw only about 7 amps at maximum rated load.

Rick I think you have a typo. Should be 230 volts 3/4 hp at about 7 amps. 115 volt at 13.8 amps.

[Mike Henderson]

Rick I think you have a typo. Should be 230 volts 3/4 hp at about 7 amps. 115 volt at 13.8 amps.
I think those numbers are a bit high. A HP is about 750watts (rounded). Let's assume a 3/4 HP motor is only partially efficient and the motor draws about 750watts to produce 3/4 HP out. At 120 volts, that would be about 6.5 amps (rounded).

Mike

[Roger Frazee]

Mike

Depends on what is meant by maximum rated load. If your talking FLC the table rating is as I posted. It doesn't seem right to me that at 3/4 hp the maximum rated load would be 1/2 of the motor table flc??? I would think the rla would not be more than 4 or 5 amps less than table value depending on the type of motor.,I've never seen motor load (amps) (nameplate amps) calculated like you did...but If I misundertood what Rick was saying then I will concede he may have reached that figure as you did....so my apologies. I thought we were talking about this motor on this thread...the maximum rated load or full load rated current as i would view it would not be 7 amps for a 115 volt 3/4 hp single phase ac.

[Roger Frazee]

After blowing a little dust off my head and looking at what your trying to say I think those numbesr you have are true horse power. I don't believe it would be correct to say maximum rated load. True horsepower I believe and I'm certainly no expert on this would be mathmatical horsepower not under any load. I'm willing to bet that is where Rick was going so I was most likely mistaken that he had a typo.

[Chip Lindley]

......and another good 3/4 horse *beat to death*!

The guy really just needed to get his motor wired correctly......

[Rick Christopherson]

For some reason I had not seen that there were several new postings in this thread.

I have confirmed the math I mentioned in a previous posting. If you were referring to the table in the NEC for amperage versus horsepower, it is very inaccurate and does not correlate to any actual motor's values.

The full (non-estimated) formula for determining a motor's horsepower is:
hp = I x V x pf x eff / 746

The powerfactor (pf) is how much phase shift exists between the current and voltage at rated load. Typically this is 0.8, but may be as high as 0.9 if the manufacturer rates the motor higher into its loading curve, which is possible if it uses better insulation in the windings. The less the motor is loaded, the lower this value. For example, an idling motor will have a powerfactor down near 0.2. This is why an idling motor will still draw about 50% of its FLA value even when it is doing no work. (By the way Roger, it is FLA not FLC, even though FLC is grammatically more correct.)

The efficiency (eff) is the various losses in the motor and is not dependant on loading. This is due to factors such as windage, air gap, and hysterieses in the iron core. This too is approximately 0.8 for a typical motor.

So working this formula backward, the current for a typical 3/4 hp motor is:
I = .75 x 746 / 120 / 0.8 / 0.8 = 7.3 amps

If it were a premium motor, I use 0.85 for both values:
I = .75 * 746 / 120 / 0.85 / 0.85 = 6.5 amps

Oh, the formula for horsepower is not an estimated formula; it is the true and accurate formula for determining horsepower. However, unless stated on the motor nameplate, the powerfactor and efficiency are estimates, but they are fairly accurate estimates, nevertheless.

[Roger Frazee]

My apologies Rick my mind set just wasn't thinking that way at the time. I sorta thought after I replied that I should look at what you said closer and run the hp formula, especially after Mike replied. But you have to live with what you say.. I just didn't feel even doing so would result in a nearly 7 amp difference from table value flc. So I just learned something.

I wonder why the training for sizing motor overload (nameplate fla) and ocpd and conductors would be from such inacurrate values? Would you happen to know why the NEC uses tables using such high values? If the tables are using the same terminology max FLA or FLC being the same why would the two methods differ so much??
You can PM me (if you find the time) as I know this is off subject for the thread.


(By the way Roger, it is FLA not FLC, even though FLC is grammatically more correct.)Thats what I thought and shot from the hip that you had pulled your figures from the NEC table when I saw that 230 volt FLC was 6.9 amps....I've seen that mistake simple as it is many times but in this case I was wrong...but dog gone it Rick I forgot you were an engineer you guys have a different way of looking at things....:) albiet probably more acurrately.

Regards

[Rick Christopherson]

Roger, I have no idea how the NEC comes up with their numbers, but the smaller the motor, the worse they become. In order to come up with their amperage for a 3/4 hp motor, they would need to have used a powerfactor of 0.4, which is ridiculously low, and that is why the amperage is double what it should be.

To compound this even further, if you had two identical products that used the exact same motor with the exact same nameplate data, but one of those products had a UL sticker (which is extremely expensive), then you are permitted to use the nameplate amperage from the motor, but for the other product, you must use the artificially inflated values in the table.

This would be fine if the table were more realistic. Keep in mind that the NEC mandates that all motors carry this nameplate data in the first place, but then prevents you from utilizing the very data that they make mandatory to appear.

[Roger Frazee]

......and another good 3/4 horse *beat to death*!

The guy really just needed to get his motor wired correctly......

That's very true and I agree we need to reach a consensus to tell a guy/gal who asks a question like this a simple yes you can or no you can't without all this motor terminology and formulas.. I think if I had it to do over again (I really didn't add much to this thread anyway) I would simply say.. sure.. but I don't think on a 3/4 hp your going to create any magical performance improvements other than those things Tom mentioned. That would let the poster decide if those things Tom mentioned would be to his liking to go ahead and make the conversion. Just make sure you understand the conversion at the motor terminals... don't have the mind set that I think it's right.. most are very simple... but ya gotta be sure..

BTW I have been forced to look back at some of my replies and I am very guilty of complicating things more than they should be....I'm a retired electrician by trade and new to the forum so trying to get my adjustment meter tuned to the needs of this forum...so bear with me....I just turned it down at least two notches....:)

[Chip Lindley]

Don't get me wrong Roger! I appreciate very much the expertise of professionals on technical subjects in these forums. But, many here get carried away with expounding on a subject far beyond the *purpose* of the thread, and the *need* of the OP. An *in-depth* explaination is wasted energy if it falls on deaf ears!

*Personal Opinion* is always plentiful in these forums! But, also, at times, *Too Much Information*! It's not all bad! The *tricks of the trade* are learned two ways--personal experience, OR recalling off-hand what we heard (or read) once upon a time. Best Regards, Chip!

[Roger Frazee]

Chip, I absolutely agree. This isn't an electrical forum. A couple things I know.. we need to avoid the cord and plug arguments, those are just silly. And 120 to 240 on power tool motor conversions need to stay within reason... there really is no harm either way.

Regards