rewire table saw

[Jacob Bowman]

Hi everyone, I would like to know if there is any real benifit to rewire my table saw for 220. Any info is greatly appreciated.
Jake

[Chuck Lenz]

I rewired my Delta 34-445 Contractors saw a few years ago to 220 after running it on 110 for about 8 years. I'd never go back to 110. I'm not going to say anymore and get into a big debate about the reasons. Try it, I bet you like it.

[Steve Clardy]

Yes. Try it, you like it.

[Jacob Bowman]

How exactly does one go about rewiring the motor and what type of switch to use, etc.

[Curt Harms]

How exactly does one go about rewiring the motor and what type of switch to use, etc.
It should tell You how to do it. If You need a manual, You can download one from the B&D/Delta web site.

HTH

Curt

[Bill Huber]

I am not an electrician but your motor has to be able to be wired 110/220. If the motor can not be wired 220 then you can't do it.

It should show on the motor the wiring for both 110 and 220, the switch will be the same and you would not have to change it.

The wiring should be on the motor plate or if not look under the wiring cover plate.

[Chuck Lenz]

I think you better call a electrician, then he can also put the right plug end on the cord and install the correct dedicated circuit for you. xxxx Hire a electrician, it's code. It's what I did, and I'm glad I did too.

[Jim Becker]

In general there is no real benefit from changing, but many folks feel more comfortable with tools wired for 240v. It uses the same amount of power and develops the same horsepower. That said, all the stationary tools I've owned that can be run on 240v have been setup that way. Personal preference.

[Carl Crout]

In general there is no real benefit from changing, but many folks feel more comfortable with tools wired for 240v. It uses the same amount of power and develops the same horsepower. That said, all the stationary tools I've owned that can be run on 240v have been setup that way. Personal preference.

sure there is a benefit. You can run smaller wires. And smaller wires are cheaper

[Austin Grote]

What if the wires are already there?:D:D

[Chuck Lenz]

I think the motors run more efficiently on 220 is maybe one bennefit and most 220 circuits that I know of are on a dedicated circuit, not branched out like alot of 110's are running lights, a radio, a TV and other equipment at the same time on one breaker. Running a dedicated 110 is one way around that.

[Jim Becker]

sure there is a benefit. You can run smaller wires. And smaller wires are cheaper

When you get into larger motors, this can certainly be true, especially with the escalation in copper prices that affect home wiring products. But in this case where the motor is a horse and a half, it's likely that it will be the same wire already in place or if new, the cost difference between 14 gage and 12 gage for the length of a circuit is minimal. Most folks will opt for the heavier wire regardless for more flexibility in the future for tool circuits.


I think the motors run more efficiently on 220 is maybe one bennefit

In general this is not so. For most 120/240 dual voltage motors, the windings are still seeing 120v. When you "rewire" them for the higher voltage, you're just changing the pathways that the current takes to portions of the windings. There have been a few tools out there that have "special" accommodations that give a little more horsepower on the higher voltage, but they are very rare.

[Greg Funk]

If your saw is currently connected to 110 and you aren't experiencing any problems then there will not be any benefit in switching to 220. You will gain a small amout of extra power (less wiring loss) and your saw will start a little quicker but it is unlikely they will be noticeable changes.

Greg

[Jake Helmboldt]

One thing that has not been mentioned (explicitily) is how well wired your shop is. Someone mentioned a dedicated 110. In my case my shop wiring is less than optimal, and wiring in a subpanel is on hold. I only have one 110 circuit so with the tablesaw it was a bit much. It only tripped once, but I switched it and it made a big difference.

If you don't have a dedicated 110 circuit or if your shop is located a considerable distance from your breakers (in an outbuilding or detached garage) you may get good increase in power.

[Bill Huber]

One thing that has not been mentioned (explicitily) is how well wired your shop is. Someone mentioned a dedicated 110. In my case my shop wiring is less than optimal, and wiring in a subpanel is on hold. I only have one 110 circuit so with the tablesaw it was a bit much. It only tripped once, but I switched it and it made a big difference.

If you don't have a dedicated 110 circuit or if your shop is located a considerable distance from your breakers (in an outbuilding or detached garage) you may get good increase in power.


If you only have a 110 circuit how could you switch your saw to 220?

[Alan Tolchinsky]

One thing that has not been mentioned (explicitily) is how well wired your shop is. Someone mentioned a dedicated 110. In my case my shop wiring is less than optimal, and wiring in a subpanel is on hold. I only have one 110 circuit so with the tablesaw it was a bit much. It only tripped once, but I switched it and it made a big difference.

If you don't have a dedicated 110 circuit or if your shop is located a considerable distance from your breakers (in an outbuilding or detached garage) you may get good increase in power.


Jake hit the nail on the head. I'd say if you are sharing that 110 volt circuit with other things then a switch to a dedicated 220 would help with more power. Check to see what else is on the circuit the saw is on. If the saw has the circuit completely to itself, then I'd say the switch to 220 may not show much imporvement. My saw was 110 and the lights would dim when I turned it on so there were other things sharing the power. So when I put it on its own dedicated 220, WOW was there a difference. So the answer is as usual: It all depends on your circumstances.

[Tom Veatch]

Hi everyone, I would like to know if there is any real benifit to rewire my table saw for 220. Any info is greatly appreciated.
Jake

Since my shop is in an outbuilding fed by a subpanel remoted off my main service entrance (I'm not an electrician, so the terminology may be wrong), I converted everything I could to 240 volt. The only reason was to reduce the voltage drop over the 150' cable feeding the panel in the shop.

That's the primary, arguably the only, advantage to running at the higher voltage. Since the wattage consumed by the tool is the same, at double the voltage, the amperage is halved. Since voltage drop over a given conductor is directly porportional to the amperage, the voltage drop (transmission power loss) is also cut in half.

I'm fairly sure that's also the reason the utility company's transmission lines run at MUCH higher voltages and are stepped down to the normal 110/220 volts to feed residential services.

[Jim Becker]

Since the wattage consumed by the tool is the same, at double the voltage, the amperage is halved.

Amperage is only "halved" on an individual hot conductor. The same total current is in play, just split over two conductors...I'm only mentioning this to clarify.

[Greg Funk]

Amperage is only "halved" on an individual hot conductor. The same total current is in play, just split over two conductors...I'm only mentioning this to clarify.
Sorry Jim, but that doesn't sound right. If your saw needed 10A @ 110V it will only need 5A @ 220V. In both cases the current is flowing through two wires a hot and neutral (110V) or two hots (220V).

Greg

[Rick Christopherson]

Since my shop is in an outbuilding fed by a subpanel remoted off my main service entrance..., I converted everything I could to 240 volt. The only reason was to reduce the voltage drop over the 150' cable feeding the panel in the shop.Finally, someone with common sense. This is one of the few valid reasons for rewiring a motor.

The typical woodworker that rewires his motor, and then assumes that the change in performance is due to the change in voltage, has completely overlooked the other changes they made in the process--the real reasons why the performance changed. :eek:

It drives me nuts reading people's stories about how changing to 240 volts has given them so much more power, when in fact, the increase in power was simply because they replaced substandard wiring with proper wiring. These people don't realize that if they had made the exact same wiring changes without changing the voltage, they would have gotten the same increase in performance.

Here are some of the simple changes that these woodworkers overlooked when they concluded that they got better performance at the higher voltage:
The number one reason for a change in performance is because the original setup included an extension cord and/or power strip. This was eliminated when they switched to 240V.
Running a close second is that the original circuit was only 15 amp at 120 volts, but the new circuit is 20 amp (or even 30 amps) at 240 volts. They not only increased the capacity of the circuit, they reduced the load on the circuit. Simply installing a 20 amp circuit at 120 volts would have given them the same performance increase.
Similar to #2 is that the original circuit was shared and overloaded, and the new circuit was dedicated to a single tool. The same results would have occurred if they installed a dedicated circuit at 120 volts.There are circumstances, such as Tom's where rewiring the tools provides a benefit for the home's wiring, but most circumstances are corrected by just replacing poor wiring with proper wiring. The windings inside the motor still see 120 volts regardless how they are configured, and the current flowing through the windings remains exactly the same. The changes are strictly because the house wiring is improved.

Why over complicate things. If you're going to fix the wiring, then fix the wiring, but there is no need to make things more complicated by changing the tool at the same time.

[Rick LoDico]

I can't comment intelligently on anything electric. However, when I had a 1.5 HP contractors saw, it kept flipping the breaker. I swithched it over to 220 and the problem ceased for good.

[Tom Veatch]

Amperage is only "halved" on an individual hot conductor. The same total current is in play, just split over two conductors...I'm only mentioning this to clarify.

Sorry, Jim. I've got to disagree with you on this. A motor running at 110 volts and developing 1 HP (assuming 100% efficiency) will draw about 6.8 amps. Thats 6.8 amps coming out of the hot line and 6.8 amps going back through the neutral line. (Not really since it's AC, but maybe you get what I mean).

Now take a motor running on 220 volts and developing 1 HP at 100% efficiency. The amperage draw is about 3.4 amps. Thats 3.4 amps coming out of one hot line and 3.4 amps going back through the other hot line. You don't add the amperages any more than you add the amperages flowing in the 110 hot and neutral lines.

Twice the voltage, half the amperage for the same power (wattage)

[Rick Christopherson]

I can't comment intelligently on anything electric. However, when I had a 1.5 HP contractors saw, it kept flipping the breaker. I swithched it over to 220 and the problem ceased for good.This is exactly the type of situation I was commenting on above. The breaker stopped tripping, so you drew the conclusion that the cause was because you rewired the motor.

In reality, it was because you put the saw on a circuit that was not loaded to near capacity. You corrected a problem in your wiring, but attributed the result with a change in voltage to the tool.

[Chuck Lenz]

Hmmmmmm, didn't I explain all that in my third post ? Or was my post too simple ? Sometimes it gets to be so hard to explain stuff to people I start questioning myself that maybe I don't comunicate very well. Is it just me, or does everyone else have this problem also ? After awhile it really gets frustrating and discourageing.

[Art Mann]

Don't feel too badly, Chuck. It is an unfortunate reality of message boards that people often don't read the posts that others have already written and just repeat the same things over and over again or fail to see the conversation in context.

[Jason White]

Higher voltage (220v) means less amp-draw -- about half I think. An electrician friend once told me that the motor will run cooler and last longer, but you won't see a real difference in power (HP).

I run mine on 110v, and even though it's on a dedicated 20-amp circuit, the overhead lights do dim a tiny bit when I first power up the saw and I have 200-amp service. The amp-draw is greatest for that split-second when you turn on the motor and then it levels off.

"Space" in your breaker panel might be a reason to stay with 110v. A 220-v breaker takes up twice as much space in the breaker box as a 110v breaker. That's because it's grabbing 110-v from each leg of the bus bar. If you only have 100-amp service for your house, you might not have enough room unless you install a sub-panel.

JW




Hi everyone, I would like to know if there is any real benifit to rewire my table saw for 220. Any info is greatly appreciated.
Jake

[Chuck Lenz]

Jason, If a motor draws 13 amps at 110, it draws 6.5 amps twice at 220.. 6.5 amps per 110 leg. it still draws the same amperage, just split.

[Greg Funk]

Jason, If a motor draws 13 amps at 110, it draws 6.5 amps twice at 220.. 6.5 amps per 110 leg. it still draws the same amperage, just split.
Per leg of what? There might be 6.5A flowing through an internal winding in the saw but you will have 13A flowing through the 110V supply. You might imagine it flowing out through the hot and back through the neutral.

Greg

[Art Mann]

Sorry, Jim. I've got to disagree with you on this. A motor running at 110 volts and developing 1 HP (assuming 100% efficiency) will draw about 6.8 amps. Thats 6.8 amps coming out of the hot line and 6.8 amps going back through the neutral line. (Not really since it's AC, but maybe you get what I mean).

Now take a motor running on 220 volts and developing 1 HP at 100% efficiency. The amperage draw is about 3.4 amps. Thats 3.4 amps coming out of one hot line and 3.4 amps going back through the other hot line. You don't add the amperages any more than you add the amperages flowing in the 110 hot and neutral lines.

Twice the voltage, half the amperage for the same power (wattage)
Sorry Tom, but Jim has it right. I have a stand alone shop with inadequate (50A, 240V) service. I wired my tablesaw and most other equipment for 240V operation because I needed to balance the current between the two 120V legs, not because I wanted to reduce the current by half. I did not gain any capacity whatsoever by running my equipment at 240V. I only insured that each of the two 120V legs was carrying about the same amount of current. In this context, the current in the two legs is additive.

[Jake Helmboldt]

If you only have a 110 circuit how could you switch your saw to 220?

Because I also have one 220 as well, which is what I use for the bandsaw and tablesaw, allowing the 110 to be used for everything else.

[Chuck Lenz]

Greg, I'm doing the Geico caveman thing here and saying to you, WHAT ? 220 is two LEGS of 110. Two hot leads ( legs ) red and black, a neutral white and a ground bare copper. 10/4 ?

[Chuck Lenz]

Greg, if you have power flowing back through your neutral, you've got problems.

[Greg Funk]

Greg, I'm doing the caveman thing here and saying to you, WHAT ? 220 is two LEGS of 110. Two hot leads ( legs ), a neutral and a ground. 10/4 ?
Chuck,

OK, I just wanted to clarify if you were talking about the internal windings of the saw or the supply lines running to them. If you are talking about the supply then you are incorrect in your earlier statement that a 13A 110V saw draws the same amount of current regardless of whether it's running on a 110 or 220V supply. When running on 110V the saw will draw 13A through the hot lead and return 13A through the neutral.

On the second part of your statement 220V wiring within a house does not include a neutral, just two hots and a ground.

Greg

[Greg Funk]

Greg, if you have power flowing back through your neutral, you've got problems.
On a 110V circuit you have no choice unless you want to return it through your body.:) On a 220V circuit there is, of course, no neutral to worry about...

Greg

[Chuck Lenz]

Okay, if 110 is returning through the neutral and back to the breaker box, where does it go from there ? Back to the power company ? LMAO ! If it does, I want a freakin refund from my power company.

[Greg Funk]

Okay, if 110 is returning through the neutral and back to the breaker box, where does it go from there ? Back to the power company ? LMAO ! If it does, I want a freakin refund from my power company.
I can't quite tell if you are being a smartass. If you don't believe me put a current meter on the neutral leg of a wire running to your tablesaw and report back to us.

Greg

[Chuck Lenz]

Ok, I'll eat a little crow on this one. On 220, black is hot, white is hot, and green is a ground. There is no neutral. I still have a hard time believeing that on 110 the neutral runs current back to the breaker box. Why doesn't 220 require a neutral ?

[Greg Funk]

Ok, I'll eat a little crow on this one. On 220, black is hot, white is hot, and green is a ground. There is no neutral. I still have a hard time believeing that on 110 the neutral runs current back to the breaker box. Why doesn't 220 require a neutral ?
On a 110V circuit you have two wires with a difference in potential of 110V. That is if you put a voltmeter across the end of the wires you will see a voltage of 110V. It just so happens that the neutral wire is tied to ground somewhere along the line (where the service enters the house I believe) so the neutral wire doesn't have any potential (voltage) with respect to ground. But the current has to return somewhere. You can't have a bunch of electrons charging down a wire with nowhere to go so they come back through the neutral. On a 220V circuit both wires have 110V potential with respect to ground but they are 180 degrees out of phase so the voltage across the wires is 220V.

Greg

[Rick Christopherson]

I have lost track of how many people are posting incorrect information in this thread, so I will just state this simply that Tom did state it correctly.

It doesn't matter what voltage your circuit is, there are two conductors with current flowing in them. Whatever current is flowing in one conductor, returns on the other. What some of you are getting confused with is the word "Neutral". This is nothing more than a name that we give to one of the conductors. The function of that conductor is no different than either of the Hot conductors, except that conductor is anchored to a ground potential as a safety measure.

If you have 10 amps flowing through a 120 volt circuit, then you will have 10 amps flowing through the hot wire and the same 10 amps flowing through the neutral.

If you have 10 amps flowing through a 240 volt circuit, then you have 10 amps flowing through one hot wire and the same 10 amps flowing through the other hot wire.

What is incorrect, is to say that you have half the current flowing in one wire and the other half flowing in another wire. It is a circuit, and whatever flows into that circuit MUST also flow out of that circuit.

The reason why the current is half in a 240 volt circuit is because the power consumed remains the same.

Chuck, Art, and anyone else that is having some trouble understanding the principles of electricity, I strongly suggest taking a look at Electricity in the Woodshop
(http://waterfront-woods.home.att.net/Articles/Electricity/electricity.htm)

[Jim Becker]

I stand corrected, Rick. I forgot about the phase relationship between the two legs of the 240v circuit. Thanks for the reminder.

[Jason White]

Yep -- correct me if I'm wrong, but they refer to that as "2-phase."

JW


Jason, If a motor draws 13 amps at 110, it draws 6.5 amps twice at 220.. 6.5 amps per 110 leg. it still draws the same amperage, just split.

[Jason White]

Me thinks we need an electrical engineer to weigh in here!

:)


Per leg of what? There might be 6.5A flowing through an internal winding in the saw but you will have 13A flowing through the 110V supply. You might imagine it flowing out through the hot and back through the neutral.

Greg

[Greg Funk]

Me thinks we need an electrical engineer to weigh in here!

:)
I did. For a more eloquently written explanation refer to Rick's post above.

[Chuck Lenz]

Rick, thanks for the link, I red some of it and I gotta tell you, I need it explained to me like I'm a caveman, or wait, maybe I am one. Anyway I should of just kept my keyboard to myself on this thread. I thought I knew something but aparently I don't. I was lucky enough to have a electrician friend that I could barter work with to get my shop rewired correctly. Aparently I didn't learn as much from him as I thought. I apologize if I confused anyone with my ignorance. I think it's time to take a break from this place before I make a bigger fool of myself than I allready am.

[Rick Christopherson]

Yep -- correct me if I'm wrong, but they refer to that as "2-phase."It is not that important, but no, they do not call this 2-phase. It is still properly refered to as a single-phase system, even though we sometimes say these two lines (the hots) are 180 degrees out of phase. This is just a more elequent way of saying saying they are pointing in opposite directions.

A proper 2-phase system would be what you would see in a stepper motor, where the two signals are 90 degrees out of phase. This is like pointing to 12 o'clock and 3 o'clock.

[Jason White]

Forgive me -- I'm trying to learn here....

So with a motor wired for 220v -- each "leg" (black & white conductors) each carry a certain number of amps -- let's say it's 6.5.

Does that mean that there's 6.5 amps flowing through both conductors "simultaneously?" Or do they alternate? And does this current then flow back to the breaker box via the "ground" (given that there's no "neutral").

Jason


It is not that important, but no, they do not call this 2-phase. It is still properly refered to as a single-phase system, even though we sometimes say these two lines (the hots) are 180 degrees out of phase. This is just a more elequent way of saying saying they are pointing in opposite directions.

A proper 2-phase system would be what you would see in a stepper motor, where the two signals are 90 degrees out of phase. This is like pointing to 12 o'clock and 3 o'clock.

[Tom Veatch]

Forgive me -- I'm trying to learn here....

So with a motor wired for 220v -- each "leg" (black & white conductors) each carry a certain number of amps -- let's say it's 6.5.

Does that mean that there's 6.5 amps flowing through both conductors "simultaneously?" Or do they alternate? And does this current then flow back to the breaker box via the "ground" (given that there's no "neutral").

Jason

Current flows "out" of one wire, through the motor, "into" a second wire and back to the breaker box. There is no current in the "ground" unless some sort of electrical fault develops in the motor.

It really doesn't matter whether its a 110 or a 220 circuit. In either case, current flows out of one wire, through the load, and back into the second wire. In a 110 circuit, one of the wires is the "hot" (black) wire and the second wire is the "neutral" (white) wire. In a 220 circuit, one of the wires is a "hot" (black) wire and the second wire is the other "hot" (any color but green) wire.

Saying it another way. Yes, in either a 110 or a 220 circuit, current flows simultaneously in both wires, but it is the same current going from the breaker box toward the load in one wire and away from the load toward the breaker box in the other wire.

[Matt Meiser]

No one has mentioned that many Delta contractor saws have an extra winding. When wired 110, they hare a 1.5HP motor. When wired 220, they have a 2HP motor. In that special case, there is a definite advantage to 220.

[Rick LoDico]

This is exactly the type of situation I was commenting on above. The breaker stopped tripping, so you drew the conclusion that the cause was because you rewired the motor.

In reality, it was because you put the saw on a circuit that was not loaded to near capacity. You corrected a problem in your wiring, but attributed the result with a change in voltage to the tool.

Thanx. May I assume that if I left it on 110 but used a dedicated breaker it would also stop flipping the breaker?

[Rick Christopherson]

No one has mentioned that many Delta contractor saws have an extra winding. When wired 110, they hare a 1.5HP motor. When wired 220, they have a 2HP motor. In that special case, there is a definite advantage to 220.
Nobody has mentioned it because it is not true. The motor in question was a 2 hp motor, and as such, is too large to run from a 15 amp circuit at 120 volts. So the motor was derated for the 120 volt configuration in order to get past UL requirements.

I personally spoke with Delta about this motor, and it did not have different windings for each configuration. It was the nameplate that was altered, not the motor.

[Matt Meiser]

As long as the saw isn't drawing enough amperage to trip the breaker. Breakers trip because the load on the circuit exceeds what the breaker will allow. So, if your saw is on a 15A circuit, and (making up numbers) draws 18A at full load (i.e. when you are ripping 8/4 maple and nearly stalling the saw) then its still going to trip. However, if you run the saw at 220V on a 20A circuut, and its drawing 9A at full load you won't trip the breaker.

The first thing you could try is unplugging everything on that circuit and making a few cuts that would normally trip the breaker. That should answer your question. In my current shop, my Delta contractor saw initially had a 110V circuit shared with my jointer. Since both weren't in use at the same time, it was essentailly a dedicated circuit. I never tripped the breaker at 110. My old shop I had to share the circuit with lights and occasionally tripped the breaker if I was doing heavy ripping. I now run it on 220 because of the power increase I mentioned above.

[Matt Meiser]

Nobody has mentioned it because it is not true. The motor in question was a 2 hp motor, and as such, is too large to run from a 15 amp circuit at 120 volts. So the motor was derated for the 120 volt configuration in order to get past UL requirements.

I personally spoke with Delta about this motor, and it did not have different windings for each configuration. It was the nameplate that was altered, not the motor.

I don't understand this (and I'm not saying you are wrong, just trying to understand.) I just checked my motor and the nameplate says 12.8A at 110V and 8.6 at 220V. Everyone knows its common practice to falsify the HP ratings, but they've falsified the max amperage?

[Rick Christopherson]

Thanx. May I assume that if I left it on 110 but used a dedicated breaker it would also stop flipping the breaker?Yes, on a properly installed circuit, the breaker would not have tripped. The breaker was tripping because you were overloading the capacity of the circuit, and also causing enough of a voltage drop in the circuit to slow the motor, which in turn, increases its demand for current.

Keep in mind that some of these dual voltage motors are large enough that they should be run from a 20 amp circuit, but manufacturers still install a NEMA 5-15 (15 amp) plug on them because that is more common (even on 20 amp circuits).

I have a portable compressor that falls into this category. It runs fine at my house where all of the wiring is 20 amp and intalled properly. When I brought it to a client's home, I could not start the compressor from an outdoor outlet because of the voltage drop in that circuit. I had to run a 12 ga extension cord to another circuit in the house.

[Rick Christopherson]

I don't understand this (and I'm not saying you are wrong, just trying to understand.) I just checked my motor and the nameplate says 12.8A at 110V and 8.6 at 220V. Everyone knows its common practice to falsify the HP ratings, but they've falsified the max amperage?No, they derated the max amperage. To put it another way, instead of "Inflating" the rating on the motor, they "Deflated" the rating.

This was necessary because otherwise they would have needed to install a NEMA 5-20 plug on the tool, and this would have made the saw less useful at construction jobsites where nearly all extension cords have NEMA 5-15 plugs, and very few outlets use 5-20 configurations.

[Matt Meiser]

How is derating different than falsifying? Meaning if this motor is really going to drawy 17.2A at 110V at full load don't they have to say so?

[James Carmichael]

Fascinating thread. I've often wondered if there was a real advantage to going 220, since, assuming the 110 circuit can handle the amperage and the wire itself is adequate, you're looking at the same watts, either way.

How about the argument that 220 is gentler on the motor, due (sure I'm butchering the electrical terms here) to lower amperage and startup torque?

[Jason White]

With 220v -- how can current flow "back" toward the breaker box if current is flowing "to" the motor through both wires?

:confused:


Current flows "out" of one wire, through the motor, "into" a second wire and back to the breaker box. There is no current in the "ground" unless some sort of electrical fault develops in the motor.

It really doesn't matter whether its a 110 or a 220 circuit. In either case, current flows out of one wire, through the load, and back into the second wire. In a 110 circuit, one of the wires is the "hot" (black) wire and the second wire is the "neutral" (white) wire. In a 220 circuit, one of the wires is a "hot" (black) wire and the second wire is the other "hot" (any color but green) wire.

Saying it another way. Yes, in either a 110 or a 220 circuit, current flows simultaneously in both wires, but it is the same current going from the breaker box toward the load in one wire and away from the load toward the breaker box in the other wire.

[Steve Milito]

With 220v -- how can current flow "back" toward the breaker box if current is flowing "to" the motor through both wires?

:confused:

The flow is in opposite directions. "What goes in, must come out" applies to any point in a closed circuit.

[Greg Funk]

How is derating different than falsifying? Meaning if this motor is really going to drawy 17.2A at 110V at full load don't they have to say so?
The current rating on a motor is the maximum continuous current the motor is designed to operate at. If the motor has no built-in protection it is up to you to protect the motor so that these limits are not exceeded. You can always exceed the max current rating on a motor if you put a big enough load on it. If you exceed the rating for too long the motor protection will trip.

Greg

[Tom Veatch]

With 220v -- how can current flow "back" toward the breaker box if current is flowing "to" the motor through both wires?

:confused:

It's not simultaneously flowing "to" the motor through both wires (2 hot wires) in a 220 circuit any more than it's simultaneously flowing "to" the motor through both wires (hot + neutral) in a 110 circuit.

At any given instant, current flows from the breaker box to the motor through one wire and from the motor to the breaker box through the other wire.

The difference between 110 and 220 is that there is a potential difference (voltage) of 110 between the single hot and neutral in a 110 circuit and a voltage of 220 between the two hots in a 220 circuit.

Also, if a neutral wire is present (XX/3 nomex cabling) in a 220 circuit, the voltage between the neutral (ground potential) and each hot is 110. The voltage between the two hots is 220. That is very easy to verify with a multimeter.

Since we are talking about AC, remember that the voltage in the hot wires, measured relative to the neutral or ground wire, varies from -110 to +110 many times per second (60 in the US, 50 in many other parts of the world). When one hot in the 220 circuit is at +110, the other hot is at -110. So the voltage difference between the two hots is 220 and the voltage difference from either hot to ground/neutral is 110.

[Josiah Bartlett]

Another EE here, although I design microelectronics for a living...

We get into a terminology quagmire when discussing mains AC in the US. Much of it doesn't apply to other power distribution systems.

The way a house (or small shop) is wired in the US is generally single-phase AC. There is a transformer up on the pole. It takes the the AC on the power companies' distribution network and transforms it down to 240 V RMS AC. (RMS means Root-mean-square, its a mathematical transform used to make Ohm's law work with AC systems). So how do we ever get 120V out of that? It's rather clever, really. There is a center tap on the transformer, which is bonded to a ground rod. This gives us the availability of either 120 or 240 volts, depending on how we wire the circuit. The "Neutral" is the center tap, bonded to ground at the panel. The "Red" hot is one side of the transformer, and the "black" hot is the other. The red and black are out of phase with each other with respect to the neutral, which is how they become 240V and not zero when you connect a load across them. Note that this does not apply in certain parts of old urban cities, which use an actual 2-phase (120 degrees out) 120V system to get 208V rms and don't offer 240V.

Unless something is really wrong with your equipment, all the current that flows in has to flow out. AC stands for alternating current, so it reverses direction 120 times per second. Thus, "hot" means its driven by the generator and "neutral" means it goes back to the generator. The neutral current can get to be pretty significant in a shop, given all the 120v tools that can be turned on. Depending on how the circuits are balanced between the red and black hot, the neutral at the panel isn't necessarily exactly ground, especially if the earth ground is poor or the subpanel is far from the main. Therefore you can get some variations in supply voltages. Wiring as many tools to 240V as you can removes the ground from the picture (other than safety) and provides more margin in a somewhat marginal panel.

In my opinion, 200A panels are a bit undersized for most modern homes. I have a 50A air conditioner, an electric dryer, an RV hookup, and an electric range. Many people also have electric hot water heaters. This doesn't leave much margin for running 2 or 3 horsepower motors.

[Chris Friesen]

In my opinion, 200A panels are a bit undersized for most modern homes. I have a 50A air conditioner, an electric dryer, an RV hookup, and an electric range. Many people also have electric hot water heaters. This doesn't leave much margin for running 2 or 3 horsepower motors.

Careful when you talk about "most modern homes"...

The majority of people in north america do not have 50A A/C units or RV hookups. I live in the Canadian prairies, and up here its very common to see 60A panels on older houses, and even most new houses only have 150A.

I have a 100A panel in my house, and I don't anticipate any problems unless I ever upgrade to a 5HP dust collector.

[Pete Bradley]

Matt Meiser[/b]]
No one has mentioned that many Delta contractor saws have an extra winding. When wired 110, they hare a 1.5HP motor. When wired 220, they have a 2HP motor. ]

[quote=Rick Christopherson;639629]Nobody has mentioned it because it is not true. The motor in question was a 2 hp motor, and as such, is too large to run from a 15 amp circuit at 120 volts. So the motor was derated for the 120 volt configuration in order to get past UL requirements.

Rick,
Thanks for finally explaining where the "extra winding" urban legend came from. I saw the a similar reference on SMC a few weeks ago, but associated with Craftsman.

I'm curious , did they actually do anything to limit the draw at 110 or just change the rating? I recognize that unless it was loaded the motor wouldn't draw the full load amps anyway.

Pete

[Mike Seals]

Another EE here, although I design microelectronics for a living...

We get into a terminology quagmire when discussing mains AC in the US. Much of it doesn't apply to other power distribution systems.

The way a house (or small shop) is wired in the US is generally single-phase AC. There is a transformer up on the pole. It takes the the AC on the power companies' distribution network and transforms it down to 240 V RMS AC. (RMS means Root-mean-square, its a mathematical transform used to make Ohm's law work with AC systems). So how do we ever get 120V out of that? It's rather clever, really. There is a center tap on the transformer, which is bonded to a ground rod. This gives us the availability of either 120 or 240 volts, depending on how we wire the circuit. The "Neutral" is the center tap, bonded to ground at the panel. The "Red" hot is one side of the transformer, and the "black" hot is the other. The red and black are out of phase with each other with respect to the neutral, which is how they become 240V and not zero when you connect a load across them. Note that this does not apply in certain parts of old urban cities, which use an actual 2-phase (120 degrees out) 120V system to get 208V rms and don't offer 240V.

.

Thanks for the post, but I wonder about the 240 part. Most commonly we use 7200VAC for the input to our residential supplies, That's 7200VAC to ground. The output is 240VAC across the taps of the transformer. The 240 would be floating, but it would be 240 none the less. Is that correct?

Now add the center tap and you get a reference to ground. Looking at one half cycle across the whole of the transformer, one tap of the transformer would be positive and the other negative. With the center tap referenced to ground, would it not be that one side of the transformer is going to be negative in respect to ground and the other positive in respect. The next half cycle we change polarity.

[Art Mann]

Amperage is only "halved" on an individual hot conductor. The same total current is in play, just split over two conductors...I'm only mentioning this to clarify.


I stand corrected, Rick. I forgot about the phase relationship between the two legs of the 240v circuit. Thanks for the reminder..

There is an important sense in which Jim was correct, whether he still believes it or not. I will illustrate with a hypothetical example. Suppose you have a shop with a 50A, 240V sub panel. Further suppose you have a tablesaw that draws 20A @120V that keeps popping your breaker. By using a clamp on current probe, you observe that 20A is flowing in one leg and 0A is flowing in the other. You have reduced the available capacity in one one leg by 20A and 0A in the other. Now, rewire your saw for 240V operation and fire it up. Use the same current probe and you will measure 10A in one leg and 10A in the other. It doesn't matter that in the second case, the same electrons are flowing in both legs. From all outward appearances, what you have done is split the original 20A in one leg into half of the current in each of the two 120V legs and reduced their individual capacities accordingly. That is the point I thought Jim was trying to make. I don't need to read a text on AC circuits to know this is true.

I have said all this because I have seen the claim on this board that you can double your power capacity at the service entrance by running your tools on 240V, which isn't true.

[Greg Funk]

There is an important sense in which Jim was correct, whether he still believes it or not. I will illustrate with a hypothetical example. Suppose you have a shop with a 50A, 240V sub panel. Further suppose you have a tablesaw that draws 20A @120V that keeps popping your breaker. By using a clamp on current probe, you observe that 20A is flowing in one leg and 0A is flowing in the other. You have reduced the available capacity in one one leg by 20A and 0A in the other. Now, rewire your saw for 240V operation and fire it up. Use the same current probe and you will measure 10A in one leg and 10A in the other. It doesn't matter that in the second case, the same electrons are flowing in both legs. From all outward appearances, what you have done is split the original 20A in one leg into half of the current in each of the two 120V legs and reduced their individual capacities accordingly. That is the point I thought Jim was trying to make. I don't need to read a text on AC circuits to know this is true.

I have said all this because I have seen the claim on this board that you can double your power capacity at the service entrance by running your tools on 240V, which isn't true.
Your comments are correct if you assume that all of the 110V equipment in your house is balanced and divided equally on both phases. There is, of course, no guarantee that this will be the case particularly if you have a small service and a few large motors. In pretty well all cases you will have more power available if you wire all major power consumers with 220V.

Greg

[Josiah Bartlett]

Careful when you talk about "most modern homes"...

The majority of people in north america do not have 50A A/C units or RV hookups. I live in the Canadian prairies, and up here its very common to see 60A panels on older houses, and even most new houses only have 150A.

I have a 100A panel in my house, and I don't anticipate any problems unless I ever upgrade to a 5HP dust collector.

I'm guessing you have either natural gas or an oil furnace. In the Pacific NW, its common for homes to have electricity be the only energy source. My power costs me 4.9c/kwh.

[Art Mann]

Greg,

I don't understand what you are saying. The effects of one load - in this case the saw - are simply added to the effects of other loads. Whether the loads on the two legs are balanced doesn't matter. Perhaps you are talking about current in the neutral wire? Can you provide an example? Maybe you ae referring to the current problem i have, which is that I only have a 50A subpanel and need to balance the load on the two legs carefully?

[Bryan Rocker]

Lots of good points here. I am glad the smart people pointed out the right way to do things. I always learn lots of useful information here.

I have a different take on things. The whole point of 220 is to buy bigger and more powerful 220 powered equipment. To me it means my 3 HP X5 saw runs like a champ. My old 110 saw never ever had the power of my X5 and it was a 15 amp motor. There is no way my 3 HP X5 could run on 110........More power....bigger tools.....that's what we all want.......

:D He who dies with the most tools wins! :D

Bryan

[Greg Funk]

Greg,

I don't understand what you are saying. The effects of one load - in this case the saw - are simply added to the effects of other loads. Whether the loads on the two legs are balanced doesn't matter. Perhaps you are talking about current in the neutral wire? Can you provide an example? Maybe you ae referring to the current problem i have, which is that I only have a 50A subpanel and need to balance the load on the two legs carefully?
A 50A subpanel should be able to support a total load of 12kW (50A x 240V). The actual load is likely less due to some derating factors which an electrician would be familiar with. The maximum one phase can support is half this or 6kW so if you want to take full advantage of your subpanel you would need to ensure that the loads are evenly distributed.

If you had a 110V air conditioner running along with a 110V dust collector and then you wanted to start a 1 1/2 HP tablesaw and they were all connected to one side of the service you would be drawing significantly more than 50A while the saw started. Depending on how far your subpanel was from the main panel you may notice a reasonable voltage drop at your saw and it would start a little slower. In any case you would be operating at the design threshold of your service. On the other hand if all three pieces of equipment were running on 220V you would only running at less than 50% of the design threshold and your saw would start quicker.

In the above scenario you would be fine if you had balanced the 110V equipment as best as possible but with a small service you need to make a little effort to determine which side each piece of equipment is connected to. With a 200A service it's not so critical since there is usually a lot more margin and any large loads like air conditioners, dryers and ovens would already be on 240V.

Hopefully this makes sense.

Greg

[Art Mann]

What you say makes sense, but I still don't understand what you are disagreeing with me about. Apparently, you are reading more into my little example than what I put there. What I said about dividing the current between two legs is true whether the load is balanced or not.

[Greg Funk]

What you say makes sense, but I still don't understand what you are disagreeing with me about. Apparently, you are reading more into my little example than what I put there. What I said about dividing the current between two legs is true whether the load is balanced or not.
You indicated earlier that you couldn't double your capacity by re-wiring everything for 220. My point is that you will generally increase your capacity if your equipment is wired for 220 and in the case where your 110V equipment is badly balanced (i.e. all on one leg) you will double your capacity.

Greg

[Rick Christopherson]

You indicated earlier that you couldn't double your capacity by re-wiring everything for 220. My point is that you will generally increase your capacity if your equipment is wired for 220 and in the case where your 110V equipment is badly balanced (i.e. all on one leg) you will double your capacity.

GregYou are not increasing your overall capacity, all you are doing is forcing the loads to be balanced between the incomming phases. Aside from this clarification, I believe (without reading everything) that everything else you stated is correct.

The same results are also achieved by simply balancing your 120 volt loads. Most importantly, is that you and other readers of this discussion, understand that this is really only applicable when you have a very small subpanel.

By the way, many people believe that all of the circuits on the right-side of the panel are on one phase, and all of the circuits on the left are on the other phase. This is not correct. Every other breaker position (vertically) alternates between the two incoming phases. While I am sure you already knew this, I am sure that other people reading this discussion may not have known this.

[Greg Funk]

You are not increasing your overall capacity, all you are doing is forcing the loads to be balanced between the incomming phases.
Agreed, but I suspect there are a reasonable number of home/shop owners who may not know to balance their loads and if they are running a number of high current 110V machines off a small subpanel could end up with a perceived diminished capacity.

Greg