Post by The Other JohnPost by MBMany says that RF burns are the worse and tend not to heal up.
When I was working on flight simulators (between TV jobs) they were using
genuine aircraft components and 400Hz power and I accidentally brushed a
finger against a live 400Hz terminal and it burnt a small hole in the skin
but it didn't need to heal because it cooked it!
I've had a few mains shocks - the most stupid was the other year when I
was changing some light fittings which had Philips Hue bulbs in them.
These tend to be left permanently powered on, and the individual bulbs
on a circuit are turned on/off/dimmed by app. Each time I did a batch of
fittings, I turned off both the wall switch and the lighting circuit at
the "fuse box". After a break I did some more. And I made the elementary
mistake of thinking "the lights are not lit, so the circuit must be off
at the wall". As my screwdriver touched the live screw on the terminal
block I must have had contact with the screwdriver and also with the
neutral. It's the first time I've had a mains shock on a circuit with an
RCD, and the fact that it tripped meant that I didn't have to pull my
hand way to break the circuit.
Others in the past have been on a non-tripping circuit before the days
of RCDs - eg when I touched the terminals where the mains cable of a
tape recorder was soldered to the main power switch. The switch was
turned off, but the feed to it wasn't...
The worst was from that same tape recorder. It used valves, so it had an
HT feed which was higher than mains: I later measured the terminals that
I had touch as about 400 V AC (before the diodes and smoothing). That
F-ing hurt: my arm throbbed for several hours.
The most bizarre was when I was unplugging the TV aerial lead from a USB
TV tuner on my (earthed) computer. I had the metal screen of the aerial
in one hand and the other hand on the computer, and I got a very
noticeable tingle. I measured about 150 V between aerial screen and
mains earth, using a high-resistance voltmeter. I went round all my
electronic equipment that was connected together: aerial went to TV, VCR
and computer; TV, VCR, hifi were all connected by audio phono plugs. By
unplugging things in turn I eventually tracked it down to the TV: one
with a CRT. With nothing connected to it apart from the mains lead,
there was about 150 V between its aerial screen and/or aerial signal
pin, and mains earth. I measured my body resistance (about 300 k ohms)
and made up resistors to mimic this (I didn't fancy using my body again
for testing, the tingle was that bad) and measured about 50 V with a
simulated body between TV and mains earth. There was evidently a fairly
high safety resistor in series, but still enough current flowed though
the "test human body" to give a voltage that was very noticeable.
After that, I attached a wire between the aerial plug of the aerial amp
PSU and the mains earth pin for the amp's PSU, so the whole signal earth
for the TV/VCR/hifi/computer setup was earthed at that one point (didn't
want multiple earths in case of hum loops).
That's the problem with modern electronic equipment: live and neutral
but not earth, so if there *is* any leakage, and there is insufficient
safety resistance, you're going to feel it.
I suppose I was unlucky that when I touched that aerial plug initially,
I was also touching an earthed computer. Any other device would have had
two wires only so there would have been no voltage difference between
the 80 V on the aerial and something else.