Lazy Electrical Question

Now why wouldn't that surprise me!

Why call it drivel when Dave might understand the difference and indeed be correct?

Or is standing on a tin tray. Also one other issue that made me give up was static electricity, which could suddenly discharge and cause spikes in the sound. It was better if you were naked, but then its not always a good look....

Brian

Strictly speaking, he's right, though. IIRC, impedance is the resistive component plus the reactive component combined vectorally from the square root of the sum of the squares, thus:

z= sqrt(r^2+x^2)

And since we're talking AC, albeit only 50hz, z is still the correct parameter to consider.

Gee, no kidding, H? Seriously, approximations ARE made for such purposes as you presumably well know. The so-called 'human body model' springs to mind. Here's an interesting article that's germane to the discussion:

Except in this case, there is unlikely to be any reactive component, so R = Z for intents and purposes.

Er, no. The human body exhibits capacitance and is more susceptible to AC than DC. Therefore one needs to focus on Z.

We used to get the apprentices with one by holding the leads tightly and getting them to wind it then reverse rolls, the trick is that if you hold the leads tightly the shock is not bad as long as you don't let go but they usually do and get the full benefit.

OOPS did not see your post.

In which case you ought to be fairly well isolated... so an answer in the order of at least several mega ohms.

Not only that, it is common in shock risk scenarios to look at the earth loop impedance - i.e. the total round trip impedance taking into account all the various aspects that will affect total current flow in any given situation.

Since the human body has no reactive components, impedance is equal to resistance. So bringing impedance up is just posturing.

Drivel. An even if it were true, any capacitance effects would increase impedance, so reducing current flow in AC.

AC is more noticeable because the quoted voltage is the RMS value.

I see you use that as a kind of flag... I presume it highlights that whatever you are about to write is drivel? That certainly seems to be the case!

No, you need to learn a bit of very basic electrical theory...

Any capacitance will be in parallel with the DC resistance. With AC that capacitance will present a reactance inversely proportional to frequency. Therefore any non infinite reactance will lower the overall impedance. (go read up on impedances in parallel)

No, again internal capacitive effects will result in the cell membranes passing AC better than DC. This applies to the skin as well. Changing voltages are better able to penetrate than static ones.

AC will also make muscle tissue attempt to contract in sympathy with the frequency. Since they can't respond at 50/60 Hz this can result in tetanic contraction and loss of voluntary muscle control. This is what can prevent you being able to "let go" of live item and thus prolonging the shock duration.

The heart muscle is most vulnerable to changing electrical stimulus, and so is far more likely to be affected and driven into fibrillation by AC than with DC. (with DC shocks you have to start the shock during a fairly short temporal window in the regular rhythm to cause the same effect)

Lastly with DC shocks, you tend to feel the initial contact and the disconnection, whereas with AC you will feel pain for the duration.

The voltage level, the magnitude of the current passed, rise time, and the frequency. Note also that nervous system effects are not the only deleterious effects of shock.

What are you going to do with the information?

In message , Dave W writes

I think he is buying the wife a new chair for Christmas. "Sit down, my love, while I plug it in ..."

Nice to know there is at least one on here with basic AC theory. ;-)

Drivel. How can one get capacitive reactance on DC?

So as usual, pompous drivel The human body can act as one plate in a capacitor when wearing insulting materials and stood on a conductive surface. There is no capacitance within it. Nor can there be as electric charges are held one the surface of insulators. Can't think of any insulating material within the human body to form a capacitor.

My apprentices can mange to get their own electrical shocks.

Me "Do not touch that cable it might be live, I'll go and turn the power off"

So I went to the cellar and turned the power off at the two CUs I could find. On the way back out of the cellar the joiner said "Your apprentice has touched the cable and he got a right belt from it".