I've noticed (in my case anyway - can't speak for anyone else) that a DC shock is much worse than an AC one. I'd sooner cop a belt off the mains than suffer a DC shock at half the voltage. I've noticed when I touch AC mains (240V where I am) I don't notice anything much to begin with; just a slight tingling which gets progressively worse over several seconds until it becomes intolerable. However, at other times I've copped 200VDC and it's been like *zap* - instant; no build-up at all - and you know all about it! I should add I have drier skin that most people so can get away with sticking my fingers in the light socket to see if it's switched on. I wouldn't suggest anyone else tries this. Just wondering if anyone else has experienced similar to me or has any theory as to why AC is a 'slow shock' whereas DC is instant?
Don't know why but in the days when kids regularly fired themselves on the third rail I remember reading that one type makes your muscles curl up and the other tends to push you away.
My only experience was working on an R1155 receiver power pack about 63 years ago. I picked it up while it was on and got 300 volts from arm to arm, I did drop it very quickly which was probably a good thing.
AC often throws you off (but not always), while DC tends to make you grip whatever you have touched tighter. For either, even when you have tested and are sure that something is dead, it is always better that you make the first touch with the back of a finger, so that if you were wrong, any tendency will be to curl away from it.
AC tends to cause muscles to contract on one half cycle and expand on the other half cycle, so the nett effect is very little (other than the pain) so you have chance to withdraw your arm. DC keeps the muscles contracted if the polarity is "wrong", so you can't withdraw your hand. Or else if the polarity is the opposite ay round, it expands your muscles, throwing your hand clear. So you have a 50% chance of not being able to remove your hand from the live wire.
I've had two mains shocks in my life, and one at about 300 V from a transformer in a valve-powered tape recorder (probable the feed to the rectifier that drove the anodes). All three were due to my unbelievable stupidity of thinking "the appliance is off so it must be switched off", forgetting that there was still power to the switch.
The third time, a couple of years ago, was a salutary lesson. Philips Hue GU10 bulbs can be "off" (not emitting any light) even when there is power to them; you turn them on and off with a smartphone app. I'd been changing some light fittings and I'd been scrupulous about turning off the wall switch and turning off the fuse to that lighting circuit each time I did a batch of fittings. Except for one time when I forgot to do either: the lamps on that circuit were off so at the very least the wall switch was off. No! That was actually the least painful of the shocks I've had because there was an RCD on the house which tripped the mains within (I presume) the stated 30 msec. The previous shocks were before the days of RCDs, so nothing tripped and I got the full belt until I pulled my hand clear.
I still have two marks on the knuckle of one hand from where it touched the live and neutral terminals of the mains switch - they look like a snake bite.
Good point, Tim. It's worth pointing out that voltage ain't everything so if the source of the current has a high impedance, you're less likely to cop a terminal shock. Both the shocks I referred to in my OP were low-Z, however (as you would expect from the mains, but the DC one was low-Z as well).
Poking around in old valve gear is a rich source of such voltages. You'll find anything up to 20kV in old oscilloscopes. But the most readily accessible contents are just 200-700VDC stuff.
In the early 60s I started messing around with electronics. I was making a valve-based amp, and setting up the power supply - around 350V DC IIRC. For some reason I was holding the 300V +ve lead in my left hand, and picked up the smoothing capacitor with my right hand, forgetting the case was connected to -ve. Fortunately, as my forefinger and thumb tips clamped involuntarily on either side of the capacitor can, my arm muscles contracted and literally threw the can over the other side of the room. It was a hell of a belt, and not one I'd like to repeat.
I suppose that these days the most likely DC shock you'd get would be a (possibly) fatal one from a charged microwave capacitor.
As an apprentice in 1956 I was sitting on a high stool at a workbench when for no apparent reason I put my bare arm on a bank of selenium rectifiers producing -400vDC, I took off across the lab.
The adage was written by people whowere professional electrical engineers, for people who were professional electrical engineers, and were not aware than anyone didn't know that.
Now, haven't you got a grandmother in need of ovine extraction lessons?
I wouldn't say that. I would say my recollection is that for a given current AC at low frequencies is more dangerous than DC: it is AC that tends to cause "can't let go" while DC may throw you off. And AC tends to fibrillation while DC tends to simple cardiac arrest. A lot easier to recover from latter than the former (especially in the days before lab/workplace defibrillators).
I mean the bit about the polarity of DC being relevant.,
I mean is it more dangerous to grab the positive terminal with your left hand rather than your right, when when putting both arms across a 1kv DC source..
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