How many sockets?

[JA2340 16]

oh come on. That's not good enough for a "teacher".

 

AC works in the same way. Just alternate it 50 times a second (50Hz)

Oh, come on!!

 

Because AC is constantly changing the voltage ... at any given instant, the calcs will be correct, BUT the voltage changes between +375V and -375V at 60 (or 50) times a second. That means that the calcs will be constantly changing.

 

So, the simplistic answer "just change it" is bullshit! Use the calcs I gave in the earlier post (if you can work out what the power factor is) and get back to me. OR, you could always get an electrical engineer to do the calcs for you - might be a better bet, asking deeply technical questions on a ski forum is a guaranteed way to get yourself into trouble with the local authorities.

[Alexander L 80]

Mantas would know.

[JA2340 16]

So ... why not ask him then?

 

OR, you could use Google to find out for yourself ... nah that's too sensible ...

[Alexander L 80]

I'd like to ask you, but you get grumpy.

[JA2340 16]

Yep, I get grumpy when peeps do not understand that there are things they need to ask a specialist. Especially when I give an explanation and it is not accepted as a reasonable answer.

[JA2340 16]

How many amps will be needed on a 110 circuit for a 1 Kilowatt heater.

 

How many for the same on a 220 circuit.

 

What heats the elements. Is it voltage or current?

at 110V, using P = V x I, or I = P / V, a 1kW element will draw 1000 / 110 = 9.09A. As an element can be considered purely resistive, we can do away with power factor for now.

 

Using Ohms law, I = V / R, we can now work out the resistance of the element. R = V / I, therefore R = 110 / 9.09 = 12.1 Ohms.

 

 

at 220V, using P = V x I, or I = P / V, a 1kW element will draw 1000 / 220 = 4.55A.

 

Using Ohms law, I = V / R, we can now work out the resistance of the element. R = V / I, therefore R = 220 / 4.55 = 48.35 Ohms.

 

If we used the 1kW element that is designed for 110V, with a resistance of 12.1 Ohms, on a 220V system, we would be drawing 18.3A instead of 9.09A, and we would probably have a fire before too long.

 

Following so far?

 

Assuming that the shock at 220V and the shock at 110V follow the same path, then we can assume that the resistance of the human body remains the same.

 

A quick google search suggests that a figure of somewhere between 300 and 1000 Ohms would be about right for a human body. Lets use 500 Ohms.

 

Back to Ohms law, R = V / I, so I = V / R. therefore at 110V, I = 110 / 500 = 0.22A. At 220V, I = 220 / 500 = 0.44A. Therefore, the higher the voltage, the higher the current that will flow through your body assuming that the entry and exit points are the same in both cases.

 

This is basic high school science.

BUT basic high school science does NOT get into AC voltages and the fact that 240V is NOT the maximum voltage reached. In fact, AC voltages average ZERO volts.

 

The values quoted are RMS values - so 240V AC varies between 375V positive and 375V negative compared with earth potential (which is assumed zero volts potential). Additionally, AC is constantly changing, so the DC calcs for any one instant may well be correct, but a poofteenth of an instant later, it will be different, and the calculations will have to reflect these changes.

 

For more detail, have a look at http://academic.pgcc.edu/ent/ENT%20171%20Online%20Project/ and scroll down to "Week 3" and have a bit of a read. You might actually see that I'm NOT talking through my arse and actually DO understand a bit about this stuff.

 

AC is a whole other issue when compared with DC. DC calculations have no relevance to AC calcs. If that's not immediately apparent, I'm out of here, leaving you to your ignorant assumptions.

[surfarthur 22]

JA, I am an electrician, I do know what I am talking about. You are correct in saying that when you are dealing with AC, you need to include power factor, however for the purposes above, talking about a purely resistive device (a heating element), then the power factor will be 1, therefore you can use the DC calculations. The human body may not be purely resistive, in fact a quick google search suggests that there will be a small amount of capacitance, which will affect the total current flowing through your body. This is where the different frequencies have an effect, however assuming the same frequency of 50 Hz and a small amount of capacitance, this would not significantly change the amount of current flowing.

 

In fact, the only difference between ohms law for DC and ohms law for AC is that instead of resistance, we use impedance, which is a combination of inductive reactance, resistance and capacitive reactance. If you are talking about a purely resistive device, then resistance = impedance.

[JA2340 16]

But 110V is typically 60Hz, while 240V is typically 50Hz, so the assumption of same frequency is not valid.

 

However, I bow to your greater understanding of the electrickery systems.