On Mon, 15 Mar 2010 09:26:32 -0500, "Dave" <>
wrote:
>
>
>"Char Jackson" <> wrote in message
>news:...
>> On Sun, 14 Mar 2010 22:57:37 -0500, "Dave" <>
>> wrote:
>>
>>>
>>>
>>>"Char Jackson" <> wrote in message
>>>news:...
>>>> On Sun, 14 Mar 2010 22:03:16 -0500, "Dave" <>
>>>> wrote:
>>>>
>>>>>
>>>>>
>>>>>"Char Jackson" <> wrote in message
>>>>>news:...
>>>>>> On Sun, 14 Mar 2010 16:28:40 -0500, "Dave" <>
>>>>>> wrote:
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>"Peter Foldes" <> wrote in message
>>>>>>>news:hnjj9t$d8b$...
>>>>>>>> Dave
>>>>>>>>
>>>>>>>> You do know the difference between a household 100v or a 347v
>>>>>>>> commercial
>>>>>>>> in the amount of their usage
>>>>>>>>
>>>>>>>> --
>>>>>>>> Peter
>>>>>>>>
>>>>>>>
>>>>>>>I can't give you a scientific example of the differences between those
>>>>>>>two.
>>>>>>>Off the top of my head I think you might be comparing single phase to
>>>>>>>a
>>>>>>>multiple, like delta or y. I can say the usage, no matter what the
>>>>>>>supply,
>>>>>>>is going to be dependant on the demand.
>>>>>>>One final attempt at trying to not look stupid is that for the same
>>>>>>>device,
>>>>>>>if it's capable of handling the higher voltage, usually the higher the
>>>>>>>voltage, the lower the current so the lower the cost to use.
>>>>>>
>>>>>> No, the cost will be the same regardless of the voltage. Usage is
>>>>>> measured in Watts. Watts are the product of voltage times current, so
>>>>>> if voltage goes up by a certain factor then current comes down by the
>>>>>> same factor. In the end, the Watts are the same, therefore the usage
>>>>>> and the cost are the same.
>>>>>>
>>>>>
>>>>>I agree with you as far a theory goes, P=I*E. But in application, if you
>>>>>have a dryer for instance. Hook it to 120V and it might use 15 Amps,
>>>>>hook
>>>>>it
>>>>>to 240V and it will probably be less than half the Amperage. So, the
>>>>>total
>>>>>power used will be less for the 240V than for the 120V.
>>>>
>>>> Come on, you know that's not true. 
>>>>
>>>
>>>Actually, it is and IIRC it has to do with wires ability to carry power
>>>more
>>>efficiently at higher voltages. As I understand it, that's also one of the
>>>reasons utilities transmit power at kilovolts instead of 120 volts.
>>>But, since I can't quote any statistics and am too lazy to google any
>>>more,
>>>I'm going to say you win. I think the difference is minor anyway so let's
>>>revert to theory and say you're right.
>>>Dave
>>
>> You're confusing Ohm's Law with transmission theory, two totally
>> different things. You correctly stated one form of Ohm's Law above,
>> P=IE. That darn equals sign gets in the way of your current position.
>> 
>>
>
>So, when you transmit power it acts one way, but when you apply it to an
>appliance it acts another? I was never taught that and never found it in
>application either. YRMV.
Yes, transmission lines have known losses which need to be accounted
for and factored into their designs, but that has nothing to do with
the current discussion. There are no long distance transmission lines
in a residential or even commercial property, so the losses from such
lines are irrelevant to the current discussion. I suspect the reason
you were never taught that is because this is far outside your area of
expertise, which I believe is what you said in a previous post.
Take your example of the electric dryer. If you have two dryers, one
designed for 120v and the other designed for 240v, the 120v model will
draw twice as many amps as the 240v model. Both dryers will use the
same number of Watts, (because P=IE), assuming the only differences
between the two models are the voltages they are designed to operate
with.
>I actually did not state Ohm's law, it is I=E/R. What I stated was Watt's
>law, which is P=I*E. You do realize one is relevant to power and one is
>relevant to resistance?
>I would agree, except you are assuming the power is the same in both
>instances, or more correctly, the current draw, which I am saying is not.
If we're having a technical discussion, then P (power) is expressed in
Watts, not amps. Current draw refers to amps, but power refers to
Watts. Watts are the product of amps times voltage. (P=IE)
>So, in my case, you can't solve for P in both 120 and 240 by assuming I is
>automatically going to be half if E is doubled.
If you're saying that "P equals IE" is wrong, and should be restated
as "P is approximately equal to IE", well we better get the textbooks
updated with this new formula. In the meantime, yes, if E is doubled
then I will be halved and P will remain unchanged. It doesn't just
work that way in the textbooks, it works that way in the field, too.
>I hope you're not going to have us Thevonize a circuit, I hated that more
>than anything. Plus, I'd have to dig out some reference books just to get
>all the steps correct. :-D
Not a bad idea to dust off the books now and then.