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The tradeoff between 110 vs 220 - please explain

You are correct, as stated in % voltage drop.

Reply to
Al Reid
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installation

I find it funny that you would criticize people for lack of information and immediately follow it with wrong information! What I think you are referring to is that there will be one quarter less power wasted due to wiring resistances. P = VI I = V/R, V = IR therefore, the power lost in wiring due to resistance in the wire is P=I^2R. When the current is cut by a factor of 2, the power lost is cut by a factor of 2 squared, or 4.

Frank

Reply to
Frank Ketchum

Ok, then maybe i'm missing smoething or you were disagreeing with the wrong person because I don't disagree with you...

Reply to
gabriel

You are right, it is downright hilarious! I left out "%" because it was implied. Shoot me.

Reply to
Toller

The thing I was taking issue with is the statement that "In other words, a

10A 220V cable will have two hot wires, each of 10A 110V" Which is not really correct. If you had a neutral and were using a device that references the neutral, then your statement is correct. However, in the context of a 220 v service, there is a 220 v potential across the two hots, not 2 sources of 110V. I was just trying to be sure that anyone else looking at this thread does not get the wrong impression.

Ok. Truce. ;^}

Reply to
Al Reid

Okay, ya got two 120v/100w bulbs wired in series, with 240v running through them. Everything works properly; eventhough it is a 240v circuit.

Then you attach a neutral in between them. No current flows down the neutral since the circuit is balanced, the lights don't change brightness; everything is precisely the same as without the neutral. Everything works properly; eventhough it is now a multiwire 120v circuit.

So, what does the neutral do? Nothing at all. There is 1.2a running through each bulb with or without the neutral. So what is the wrong impression?!

Reply to
Toller

You picked a balanced condition. Just one of many posibilities. Do the same with a 100w and a 60 w. The neutral will cary the imbalance. In fact, if you measured carefully, you would find that in your scenario, that there was a small current in the neutral. In the case of a 220v motor, which was being discussed, there is no center tap. The windings are wired in series for 220 and in parallel for 110. So what. In the absence of a neutral, you have a 220v single phase feed. Period. You can try to call it two 110v feeds, but you would be wrong. Add a neutral and you would then be correct.

There are so many misleading answers to electrical questions that it is best to be precise and correct when providing information. Just because "you could say that" does not make it technically correct.

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Reply to
Al Reid

As you stated. Two 110/120 legs is a common misconception, as is the misconception that everything always has to be referenced to a grounded conductor, or that there is something sacred about center-tapped transformer configurations.

Reply to
ATP

Pardon me for interrupting - but I have to gloat about the 3-phase 240 volt supply at my house.

Reply to
Don Mackie

Well then do it right! 600 amp @ 480 volt in my house/shop

William....

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Reply to
William

If only you knew what you were talking about.

Depends on what you mean by 'negligible'. To coin a "Clinton". :)

To deliver the same amount of power to the load requires *twice* as much current at 120V as is needed at 240V. Losses in the wiring, etc. are proportional to the _square_ of the current. Thus the losses in the wiring are *four*times* greater at 120V vs 240v, for the same power at the load.

In a properly designed system, these losses are "relatively small" at either voltage. But, regardless, the losses are only 1/4 as large when you run things at 240V.

EVEN WITH 'properly sized' wiring, the allowable voltage drop _in_the_wiring_ between the panel and the device can be several volts. A 5V drop in the wiring, with a 15A load, and the _wiring_ is giving off as much heat as a

75 watt light bulb. And that's "within specifications" for a properly constructed circuit.

You're free to think whatever you like. :)

Needless to say, the 'quality' of any given motor is *unchanged* by being run at 240V instead of 120V. Regardless of whether it's a 'cheapie', or a 'top of the line' unit.

Motors are, in general, more efficient when operated at higher voltages. This means the internal "losses" are lower at higher voltages. This means that there is, all else being equal, _less_ heat build-up in the motor, when run at higher voltages.

Excess heat _is_ one of the biggest enemies of longevity.

Reply to
Robert Bonomi

In the interest of further belaboring the point and to do a sanity check on myself consider the following:

Given a dual voltage 120/240v motor where the FLA is 20/10. When operated at 120 vac the windings are wired in parallel and at 240 they are wired in series.

Ok so far? Lets consider that the winding resistance of .5 ohms per winding and that the heating is a result of I^2 * R.

For the 120v case, the effective resistance of the parallel windings is 0.25 ohms ( [R1 * R2] / [R1 + R2]. The heating loss would therefore be 20^2 * 0.25 = 100Awtts

For the 240v case the effective resistance of the windings in series is 1 ohm ( R1 + R2 ) The heating loss would be 10^2 * 1 = 100 Watts.

Then why are the losses considered to be more when running at 120v rather than 240v? Looks to me like the same amount of power is lost due to heating.

Reply to
Al Reid

on myself consider the following:

they are wired in series.

winding and that the heating is a result of I^2 * R.

0.25 ohms ( [R1 * R2] / [R1 + R2].

ohm ( R1 + R2 )

There isn't any difference noticed in the motor itself. As you note, the motor itself sees the same voltage and current on it's windings. The losses are generated from the wiring which supplies the motor. All the way from the main electrical panel, through any sub panels, to the outlet and though any extension cords.

Frank

Reply to
Frank Ketchum

Go with 220 when you can. Machines will run cooler and more efficiently

John

Reply to
John Crea

"Al Reid" wrote in news: snipped-for-privacy@corp.supernews.com:

Two things - one is that these are AC motors, and so there's inductive effects (so I^2 * R isn't accurate, you need to consider the impedance and the phase angle); and secondly because you're drawing more current at 110, the drop in the circuit to the motor is greater, in order to produce the same output power you need more than twice the current than the 220 motor draws.

John

Reply to
John McCoy

"Bob Davis" wrote in news:6dcUb.11892 $ snipped-for-privacy@newsread2.news.pas.earthlink.net:

Buildings catch fire due to electrical problems fairly often (I wouldn't be surprised if it wasn't the most common cause of fires now-a-days). Sometimes it's due to improper wiring ("oversized" breakers, etc), sometimes it's due to degradation of the wiring over time (the old frayed extension cord phemonemon).

Which isn't to say the OP might be at risk of fire - but in looking at the worst case problem he could see, certainly fire would be that, particularly if his shop is in an elderly building.

John

Reply to
John McCoy

Good, we agree on that. So the 20A 120v motor will need to be fed from a 30 A breaker using #10 wire while the 10A, 240V motor will need to be fed from a 15A breaker using #14 wire. Givint this installation, there will be negligable difference in the performance of the motor when the system is examined in total.

Reply to
Al Reid

Like money $$$ ???

Well I guess if you don't run any motors larger then about 1 hp, you really have no need for 3 phase power. On 2-3 hp motors it's debatable on the savings, but they start better, and cost a lot less to run and purchase even it that range. At 5 hp and over there is no contest. And YES the industrial tools are the way to go, in another thread there was some one complaining about the PATHETIC performance of a sander and its cheep import motor popping off the overload, you will not hear me complaining about not enough power running my 20hp industrial sander :-) That size motor can be wired @ 480v using ONLY 10ga wire in 3/4" conduit, run a smaller breaker, smaller starter etc.. saving even more $$$$

William....

Reply to
William

30 A breaker using #10 wire while the 10A, 240V motor will

installation, there will be negligable difference in the performance

I agree. I'm not one that thinks the losses from wiring is a big deal, I was just sumarizing the other side of the argument. Truth be told, I like

240volt runs mainly because I can run smaller wire which is cheaper and easier to use.

Frank

Reply to
Frank Ketchum

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