I always wonderd what they meant, when "Hot wire" was mentioned!
It's used in the same sort of colloquial manner as Brits talk about the "Live" wire.
Would the 55v break down your resistance & kill you! or would the current take the route to the centre tap to earth, because it has the least line of resistance?
If you got yourself connected across one side of the supply and earth then, yes, you'd be hit with 55V, the current path being from one end of the transformer's secondary wiring through your body and earth back to the center-tap of the secondary winding.
prove fatal under certain circumstances, but it's far less likely to kill than a 110V shock, everything else being equal.
The whole point of using the center-tapped arrangement is that by far the majority of electric shocks are sustained line-to-earth, i.e. somebody accidently touches an energized terminal while standing in a puddle, or leaning on earthed metalwork.
Shocks sustained line-to-line (or in a regular 240V UK system, line-to-neutral) are far less common.
If you used a simple 110V secondary winding with one end grounded, then a line-to-earth shock would be the full 110V. The center-tap system ensures that this most common method of getting a shock reduces that shock potential to 55V.
If you held both current carrying pins, one in each hand, you get 110v 'zap', you can't let go, would this break down your resistance & kill you?
If you were "stuck" across 110V hand to hand for any appreciable time, then it could very well prove fatal. A hand-to-hand shock is generally one of the most serious ways to be shocked, as the current passes directly through the chest where it can affect the heart and respiratory system.
So what is the safest & why? ... a 240v with RCD, or 110v secondary supply?
I think this could be very much open to argument. I always like to point out that a 30mA RCD is not
an absolute guarantee against electrocution, despite the fact that many people are left with that impression from the way they are marketed these days. A sustained shock at just below 30mA could certainly be fatal to some people in certain circumstances.
One other point to keep in mind when looking at one system versus the other is that the 110V CTE arrangement for power tools was introduced long before 30mA or even 100mA RCD protection was commonplace.
30-odd years ago, the earth leakage protection, where provided at all, would be more likely to be in the order of 500mA. A 240V shock which results in a current of that magnitude through the chest for anything but the briefest of periods is almost certain to result in ventricular fibrillation.
[This message has been edited by pauluk (edited 07-12-2004).]