Electrical Ground

[flecc]

It wasn't a direct connection then.. 230v accros the body , driving say 100 ma will cause all the muscle groups it contacts to contract violently. If a live wire is grasped by the hand, the contraction makes it impossible for the person to let go..if it were on the back of the hand, it would throw the arm away into safety...

Very definitely a direct connection in, on one occasion last September grasping what turned out to be live when I thought it had been turned off. But I wasn't earthed at that time so no through path and on other occasions I was always wearing rubber soled footwear.

The rejection, what you call throwing away, is what always happens to me.
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[danielrlee]

If a live wire is grasped by the hand, the contraction makes it impossible for the person to let go.

I thought that was the case for DC, but with AC, don't the zero crossing points of the alternating waveform provide an opportunity for the muscles to expand and therefore let go of the wire?

 

[Danidl]

I thought that was the case for DC, but with AC, don't the zero crossing points of the alternating waveform provide an opportunity for the muscles to expand and therefore let go of the wire?

Afraid that is the fantasy going back to Westinghouse and Edison. The voltage does go through 0 v but it is back up to lethal levels much quicker than nerves or muscles can respond. A full cycle at 50 Hz is 20mS , a half cycle 10mS , and significant voltage from 1mS from crossover.
To reiterate muscles will clench and no act of will will unclench it's involuntary. Other muscle groups outside the path can of course respond. A colleague of mine, a fellow physicist was repairing a vacuum cleaner in a reasonably insulated room. He inadvertently touched the live , clenched fist , but because of the insulation in the floor, was below that needed to trip the Resiidual Current detector RCD and so remained trapped. He was trying to move a leg around to contact the radiator, in order to increase the current above the trip, as steam and smoke was coming out his mouth when his wife came in and switched the socket..
He survived that encounter , but died prematurely and I believe that it may have contributed...

 

[Woosh]

Is there a technical reason that metal framed ebikes don't use the frame as a conductor, like cars do? Seems a logical way of reducing wiring looms.

yes, there are.
firstly, aluminium oxydizes very easily and aluminium oxide is an excellent insulator, so not good to use in place of copper wires. Secondly, corrosion. Whenever you have two metals joined together, aluminium and the weld metal, you create a battery. If there is no current flowing through the metal A / metal B junction, then all is fine. If there is a current, then metal will migrate and chemically react. So you don't want any current flowing through your frame.