Why 240?

[Stefan Antwarg]

I have 3 tools (table saw, band saw, lathe) that can be wired for 240. In fact, in my old house I did have them wired for 240. When I moved to my new place, I didn't have the 240 volt outlets, so I rewired my tools for the 120 outlets. There is no difference that I can tell in the performance of the tools. But I had always been under the impression that having them wired at 240 was more economical, since it draws less amps. Then the other day I had an electrician rewire my basement for my shop. I decided not to have him put in any 240 outlets for my tools. He told me that it doesn't gain you any more power and that it was LESS economical. Because you have to double the amount of amps it draws.

So, what advantange to you gain from having 240?

Stefan

[Ken Fitzgerald]

Stefan,

Power is sold in kilowatt hours. One of the many formulas for power is P=IxE..where P = power in watts....I= current in amps....E= Voltage in volts.
In short...the power consumption should remain the same as when you halve the voltage you double the current. It should cost the same.

The one possible difference you might see...I repeat might.....because you are doubling the voltage there is twice the starting potential across the motor windings and therefore...your saw might spin up faster on initial startup and recover faster if bogged down when cutting.

Somebody correct me if I'm wrong........

[Chris Padilla]

True, the power is the same regardless of the voltage you use. The motors could care less if they see 120 V or 240 V.

Where it makes a difference is in power loss across your wires running in the wall. The wires feeding your motor will have less current running through them and therefore run a tad cooler.

After all, when the power company delivers power to your house, it comes to the pole outside (or buried in a dungeon) at voltages in the 500,000 V range. It is then stepped-down via a transformer to 240 V into our homes. Why so high a voltage? Easy...they can use small wires to carry the current. If they brought the voltage in at say 50,000 V...the current would be 10x higher and therefore require a thicker wire...more money in wires.

As to the motor...some people SWEAR the motors run better and have more torque when wired for 240 V. I forget the reason why (if it is true) but do a search here...there are several long threads on this very topic.

[Ralph Steffey]

Most people will tell you you will not gain anything but on my old craftsman radial arm saw on 110 it had no ball at all and would bog down on most cuts I wired it for 220 and it cuts great with no bog so I think 220 is better.

[Rob Russell]

Watts is watts. A saw that draws 15 amps @ 120v will draw 7.5 amps @ 240v. Either way it's still 1800 watts and that's what the meter will record.

The electrician that told you that running the tool on 240v would use more amps was flat out wrong. A motor that can be run on either 120v or 240v will use half that amperage at 240v that it uses at 120v. It's really that plain and simple.

So - why run a machine on 240v?

The best reason is startup current. By running on 240v, you draw power from both busses in your panel. That means the momentary current to get the motor spinning is split between the 2 legs coming into your house. That means the voltage drop caused when the motor starts is split between the 2 legs in your house. That means that all the 120v appliances in your house will see less of a voltage drop (lights would dim less) by running your machines on 240v rather than 120v. Less voltage sag at startup will mean that a motor will spin up faster which is why it might seem like a 240v motor "bangs" to life a little more quickly than the same motor wired for 120v.

If you had l-o-o-o-o-o-o-n-g distances between your panel and machines, you'd see sightly less voltage drop in the branch circuit wiring to the machine at 240v.

[Alan Tolchinsky]

when I switched my Delta contractos' saw I noticed two things. First it starts up a lot faster; it just jumps to life now. This has been confirmed here. But secondly it seems more powerful too. But I think the reason is that I had too many tools, lights, etc. on that 110 line I used to use for the saw. I think even the lights were on it because, as I recall , they used to dim when starting the saw. So more than anything it was just giving the saw a dedicated line that has helped. And no more dimming lights is nice. So if you are not having these problems I'm not sure switching would make much sense. Alan in Md.

[Tim Morton]

I am under the impression that some 2HP or larger motors will draw too many amps at 110v for most houseehold (15amp)circuits. Both my DC and Jointer will draw more than 23amps at 110, so my plan is rather than expand the 110v circuit to cover this why not add 220v and draw much less amperage?

[Brad Olson]

I am under the impression that some 2HP or larger motors will draw too many amps at 110v for most houseehold (15amp)circuits. Both my DC and Jointer will draw more than 23amps at 110, so my plan is rather than expand the 110v circuit to cover this why not add 220v and draw much less amperage?

One small differene between 220 and 110 is that the 220 pulls off both legs and thus balances its load across the legs. This makes it easier to make sure your equipment isn't pulling too hard on one leg. Not a huge deal, but if you run off of a sub panel it it makes planning easier (i.e. if both the DC and TS are on 220, you don't have to make sure they are on opposite legs to balance the load like you would with 110).

[Ken Garlock]

True, the power is the same regardless of the voltage you use. The motors could care less if they see 120 V or 240 V.
....
After all, when the power company delivers power to your house, it comes to the pole outside (or buried in a dungeon) at voltages in the 500,000 V range. It is then stepped-down via a transformer to 240 V into our homes. Why so high a voltage? Easy...they can use small wires to carry the current. If they brought the voltage in at say 50,000 V...the current would be 10x higher and therefore require a thicker wire...more money in wires.

Hold the phone, Chris, what is Cisco putting in the coffee out there I seriously doubt that you will see any 500KV lines in anything other than a cross-country tower line. I know for a fact, per the local line men, that we have 7200V on the poles coming up our driveway. Consider that, if under some circumstances, I use all the ampacity of my distribution panels, 400 amp, that is only 13.33 amp load on the 7200V side of the transformer.

I agree that voltages at 500KV and above are used, but only with cross country high-towers. Those applications can sometimes be recognized because the conductors are grouped in fours with four point spreaders. This gives a larger effective surface area and thus reduces the tendency to form coronas.

I am not saying that 7200 is all that is distributed. A case on the Discovery Channel was of a lineman who lost his hands and part of his forearms because he was careless and somehow got into a 22KV line in the city. The same program showed maintenance being done on a 500KV line using a helicopter since it is too dangerous to attempt service by first climbing the tower and transferring to the cable/line. During a practice rescue from a 500KV line, the announcer said several times that the men working on the live lines could not come within 19 feet of the towers or they could be electrocuted.

[Wm Bauserman]

There is no difference in voltage drop between 120 and 240 circuits. The absolute voltage drop is always the same, for example, if it is 12v at 120 it will be 12v at 240. The gain is because percentage-wise, that 12v is half as great at 240v as it is as 120v (ie, 5% drop to 10% drop). And if your motor wants to pull 1800 watts, what it can't get from the voltage, it will try to make up in current (P=VxI). So, if these numbers were realistic (which the v drop should never be this high),

1800W/(120-12)V = 16.6A

1800W/(240-12)V = 7.89A (not 16.6/2 or 8.3A)

In real life they will be much closer, and there are other factors to consider, but overall, 240V is a better choice for a motor if it is available.

[Steve Clardy]

Here we go again. Your electrician needs to rethink what he told you.

All I can say is, I have converted one tool from 110 to 220, and did notice the difference. And---I didn't have a wiring problem before converting over.
Steve

[Ken Garlock]

There is no difference in voltage drop between 120 and 240 circuits. The absolute voltage drop is always the same, for example, if it is 12v at 120 it will be 12v at 240. The gain is because percentage-wise, that 12v is half as great at 240v as it is as 120v (ie, 5% drop to 10% drop). And if your motor wants to pull 1800 watts, what it can't get from the voltage, it will try to make up in current (P=VxI). So, if these numbers were realistic (which the v drop should never be this high),

1800W/(120-12)V = 16.6A

1800W/(240-12)V = 7.89A (not 16.6/2 or 8.3A)

In real life they will be much closer, and there are other factors to consider, but overall, 240V is a better choice for a motor if it is available.

What you experience on any wire are two things, 1) heating due to I-squared-R loss. Second is voltage drop which totally dependent on the current in amps, and the resistance of the wire.

Consider:
a 100 foot run of wire with a total resistance of 2 ohms. The supply voltage is 120 volts, the load on the wire is 10 amp. the voltage drop is 20 volts. 2X10, the power loss is 10*10*2, or 200 watts. That is a big loss.

Now consider the same problem with 240 volts. Further, let us state that the load is now configured for 240V, and that it will draw 5 amps. The heat loss now becomes 5*5*2 or 50 watts. The voltage drop on the line is 5*2, or 10 volts.

We can conclude that:

a) voltage drop is a function of current on, and resistance of, the wire. When the resistance of the wire is constant, the voltage drop is a function of the current in the wire. Hence, a 1200 watt load, (120v*10a) with have a bigger voltage drop than a 1200w load at 240 volts(240v*5a) from the example above.

b) Heat loss in the wire due to the resistance of the wire varies as the square of the current in the wire. Double the current and the heat loss goes up by 4.

[Stefan Antwarg]

Well, some of you guys are way way over my head. But, from what I can gather, it sounds like the primary reason to go for 240 is to reduce or prevents your lights from dimming when using these machines. Also for a quicker start-up. Yeah, when my tools were at 240, I noticed how much quicker the table saw got to full speed. But the difference is less than a second. I just don't see that advantage.

As far as my electrician, he seems like a compentent guy. He did a very good job with wiring the area. He also gave me some better lighting. It was done very neatly and exactly as I requested. Perhaps his theory needs re-thinking. He was trying to say that since the power come in on 2 legs, the reduced amperage has to travel on both - doubling that reduced amperage.

Sorry for my extreme rudimentary language. But thanks for all the replies.

Stefan

[Wm Bauserman]

What you experience on any wire are two things, 1) heating due to I-squared-R loss. Second is voltage drop which totally dependent on the current in amps, and the resistance of the wire.

Consider:
a 100 foot run of wire with a total resistance of 2 ohms. The supply voltage is 120 volts, the load on the wire is 10 amp. the voltage drop is 20 volts. 2X10, the power loss is 10*10*2, or 200 watts. That is a big loss.

Now consider the same problem with 240 volts. Further, let us state that the load is now configured for 240V, and that it will draw 5 amps. The heat loss now becomes 5*5*2 or 50 watts. The voltage drop on the line is 5*2, or 10 volts.

We can conclude that:

a) voltage drop is a function of current on, and resistance of, the wire. When the resistance of the wire is constant, the voltage drop is a function of the current in the wire. Hence, a 1200 watt load, (120v*10a) with have a bigger voltage drop than a 1200w load at 240 volts(240v*5a) from the example above.

b) Heat loss in the wire due to the resistance of the wire varies as the square of the current in the wire. Double the current and the heat loss goes up by 4.

Ken, you are correct, I wasn't thinking at all (or can I claim I was only considering the very useful real world situation of the constant current source ).

But in reality, the current is still less than half at 240 of what it is at 120. If you use your situation of a 2 Ohm resitance in the wire and a 1200 Watt load.
Then the current draw at 120V is roughly 12.68A and at 240V it is about 5.23A.

[Kirk (KC) Constable]

I get a kick outta threads like this. One day, probably after all of us are looooong dead and gone, somebody will post the actual true answer that nobody can possibly dispute. That's not been done yet on any forum I've visited in several years. Which is not to say that lots of folks don't KNOW the answer, just that they'll never be able to convince everybody else that it's true.

Personally, I don't care one way or the other. If it comes prewired for 115, I figure it'll work just fine that way. If it NEEDS to be 230, they'll make it so at the factory. I've only rewired one thing (dust collector), and that was only because I had an outlet handy.

KC