240V vs 280V

I would like to know if there are any advantages to using 240VAC versus 480VAC. I know for motor controls 240V requires higher amperage and components must be rated higher but this doesn't mean we are wasting any more energy than 480V?

DaveW said:

I would like to know if there are any advantages to using 240VAC versus 480VAC. I know for motor controls 240V requires higher amperage and components must be rated higher but this doesn't mean we are wasting any more energy than 480V?

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Energy or Watt or VA is Voltage X Current. Theoretically you have the same power requirement at 240 as 480 because of this principle. But in praticality the higher voltage the lower loss due to voltage drop and bleedoff (lack of better wording on my part.) However this all comes to a screeching halt when you think about insulation needs and saftey of working on circuits.

But in real world situations I'd much rather use 480VAC then 240VAC because of the smaller wire (less amps) and available power to circuits. You get much more power from a 480VAC 30 circuit then a 240VAC 30 amp circuit.

Just my 2 cents.

Chris S said:

However this all comes to a screeching halt when you think about insulation needs and saftey of working on circuits.

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240 will kill you just as easily as 480 will.

240 will have higher current thus higher IR and I2R drops even with larger wire. Other than that very small differece in correctly wired facilities there is no difference electrically.

480 equipment is higher cost which is probably the greatest consideration.

Dan Bentler

we were always taught that it takes 1/64 Amp to palpitate the heart, at any voltage.

480V equipment more costly? From my experience, it's just the opposite.

Most motors are dual voltage, so there's no comparison.
Most equipment (panels,disconnects) are higher, unless they are 3 phase, at which point the cost difference is minimal.
The biggest consideration comes from protection,i.e., fuses. Fuses rated at 240VAC will not work at higher voltages, while 600 VAC fuses will work on 240VAC. This same concept applies to equipment as well.
However, as already pointed out, higher voltage = less amps = less kW = less money on power bill.

OK, this is hearsay and I haven't checked the validity. I was taught that 110V tends to cause the heart to fail flaccid and easy-ish to restart. 415/480V causes the heart to fail contracted and easy-ish to restart. 240V leaves the heart fluttering and a lot harder to restart. Fluttering isn't the right word and makes me think of women and heaving bossoms but I am sure you get the drift. Now the only problem is how to get the heaving bossoms out of my mind so that I can get back to work.

Bryan

BryanG said:

OK, this is hearsay and I haven't checked the validity. I was taught that 110V tends to cause the heart to fail flaccid and easy-ish to restart. 415/480V causes the heart to fail contracted and easy-ish to restart. 240V leaves the heart fluttering and a lot harder to restart. Fluttering isn't the right word and makes me think of women and heaving bossoms but I am sure you get the drift. Now the only problem is how to get the heaving bossoms out of my mind so that I can get back to work. Bryan

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Getting exited (thinking on fluttering bosums or mammaries in motion) can also lead to heart problems. You need to concentrate on something and get your mind elevated - please derive algotithm correlating mammary movement to heart rate in males aged 20 thru 70 in 10 year increments.

In USA the thinking is I believe 10 mA or greater than 30 volt can create heart problems. The higher the voltage then the more assured youre gonna get a problem. The other thing with higher voltage is the burns from current flow in body. Guy here at marina got his right foot damaged so bad they amputated when sailboat mast contacted 15kV line.

Dan Bentler

Tharon said:

240 will kill you just as easily as 480 will.

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Ok yea your right its the Amps that kill you. I also have a pet pieve on that subject aswell.

But 480 has a tendency to hold you on a bit longer then 240

But I'm guessing you already knew that

Chris S said:

Ok yea your right its the Amps that kill you. I also have a pet pieve on that subject aswell.

But 480 has a tendency to hold you on a bit longer then 240
But I'm guessing you already knew that

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I dont know whether that holding stuff is a myth or not. After the ONE time I got it on 450 3 phase I have had absolutely no desire to be a test subject. I think that as voltage goes down it tends to hurt less but I have no desire to test that theory either.

Dan Bentler

leitmotif said:

I dont know whether that holding stuff is a myth or not. After the ONE time I got it on 450 3 phase I have had absolutely no desire to be a test subject. I think that as voltage goes down it tends to hurt less but I have no desire to test that theory either.

Dan Bentler

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I think it is a Myth. My first Circuits course, the professor told us that it was the frequency that did the holding. Apparently the 50Hz is "safer" than 60Hz (Both can still very much kill you, so stay away regardless).

Which is why many people might think that 230V is "safer" than 480V, since the European is predominantly 230V/50Hz and US is 480V/60Hz.

Tharon said:

I think it is a Myth. My first Circuits course, the professor told us that it was the frequency that did the holding. Apparently the 50Hz is "safer" than 60Hz (Both can still very much kill you, so stay away regardless).

Which is why many people might think that 230V is "safer" than 480V, since the European is predominantly 230V/50Hz and US is 480V/60Hz.

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So if it is the frequency that is doing the holding then DC must be perfectly safe?? From working on submarine battery I can vouch 250 VDC hurts also.

Kind of funny story
Psyochologist is doing rat study and doing negative feedback with 250 VDC on the cage bars. Rats figured it out and stood on every other bar (equal potential). Psych is going nuts trying to figure out why rats are not responding until he sees them straddling one bar. Asks an electrician what to do and gets told use 3 phase they cannot straddle 3 bars, thus you will be able to zap them. Psych hooks cages to 480 V 3 phase and cooked all his rats - forgot all about a current limiting resistor.

Supposed true story from University of Washington - probably another myth but who knows??

Dan Bentler

leitmotif said:

So if it is the frequency that is doing the holding then DC must be perfectly safe?? From working on submarine battery I can vouch 250 VDC hurts also.

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DC is different. DC is Never 0V, while AC passes 0V quite often.

Supposedly (according to my professor) 50Hz is less likely to "lock" you in place because of the way the human body responds to 50 vs 60.

I've got no proof though, just what my prof said.

It is more complicated:

The danger depands on the amount of current and the time the current flows. The amount of current depands on the tension (voltage) and of course the total resistance. The resistance depands of the path the current takes, the frequency, condition of the skin (dry of wet) and the contactvoltage.

The higher the contactvoltage the lower your body (skin)-resistance gets. Different sources use different values. My source is AIB-Vincotte: Lower then 50 Volt your resistance goes way up to more then 8 kOhm, 230 V gives you 2 kOhms.

The total resistance depands on: contactresistance body-machine + bodyresistance + contactresistance feet-earth. For this last resistance, wood gives you a high resistance, concrete a low risistance.


What killes you is:


W = P.t = U.I.t = R.I^2.t

I have some curves about different parameters, but the one parameter that you can not calculate because it is different for every situation is the total resistance.