General > General Technical Chat
Got shocked by 120VAC
LECKO:
As a maintenance mining elec by trade, finished my apprenticeship in 1968 at the golden age of 21, with the UK National Coal Board, I won't quibble with voltage and current, we had both. 3.3Kv at that time underground, to later 6.6Kv and when I finished in NSW Australia 11Kv underground with 300amp CB's. I was also authorized to enter the main switchyard where 66Kv was around. My engineer said to me after being authorized as a Leading Hand Elec, "John, if you have to enter the switchyard, stay on the marked foot paths, DON'T stray from them, 66Kv can jump a fair distance, and we don't want to scrape your remains up off the floor".
During my first year training at the area training center, we did week about in the first year, one week training center, one week Tech College, we covered this issue of voltage v current and AC v. DC shocks.
TOO MANY VARIABLES to argue over, wet conditions, whether the person shocked was fit, tired, sick, etc, etc.
Severe shock from one hand through the torso and out the other hand was the most dangerous way to have a shock, second was left hand through the body to ground, both are through the heart.
I used to take some dangerous risks when the voltages were 440 and 550 three phase, once we installed 1.1Kv equipment the risks stopped, and it was to the letter of the law. "Isolate and ground" Which is still my present attitude on ALL voltages above 25 AC., and on the test bench, left hand behind the back when checking voltages with a multimeter.
That one shock too many could be the one that makes your wife a widow. In my late teens I worked with an electrician who survived 3.3Kv in an illegal situation underground in a coal mine. It was covered up!
When I was a leading hand elec, I got a phone call to get down to another district in the mine, one of my young elecs had got burned, cost be three hours in paperwork, report for the Elec Mines Inspector! The lad was lucky, burns to the arms and face, he broke the rules accidentally on a 1000 volt circuit.
Zero999:
--- Quote from: Siwastaja on June 12, 2021, 07:21:49 am ---If it's "current that kills", then you may want to try to explain yourself how RCDs are able to save lives. Note, they can't limit current, it is what it is; they only limit the time.
No need to reply to me; I'm not interested in social games. I prefer intellectual honesty so work it out in your own head. It's not all that complex if you choose to ignore rules developed 100 years ago for explaining things to laymen using bad analogies. Instead, work with the basic units available to us scientists and engineers. Voltage, current, resistance, impedance, power, time, energy... For example, a high-impedance high-voltage supply forms a classic voltage divider with the body impedance, and the lower the body impedance, the lower the voltage over body. Think about all of this instead of playing social games.
--- End quote ---
It's pretty obvious time is a factor, as well as current. As mentioned above, a Van de Graaff generator discharging into someone might give a peak current of 50A, but it's such a short duration, it doesn't cause any damage.
GlennSprigg:
--- Quote from: Zero999 on June 12, 2021, 02:00:51 pm ---
--- Quote from: Siwastaja on June 12, 2021, 07:21:49 am ---If it's "current that kills", then you may want to try to explain yourself how RCDs are able to save lives. Note, they can't limit current, it is what it is; they only limit the time.
No need to reply to me; I'm not interested in social games. I prefer intellectual honesty so work it out in your own head. It's not all that complex if you choose to ignore rules developed 100 years ago for explaining things to laymen using bad analogies. Instead, work with the basic units available to us scientists and engineers. Voltage, current, resistance, impedance, power, time, energy... For example, a high-impedance high-voltage supply forms a classic voltage divider with the body impedance, and the lower the body impedance, the lower the voltage over body. Think about all of this instead of playing social games.
--- End quote ---
It's pretty obvious time is a factor, as well as current. As mentioned above, a Van de Graaff generator discharging into someone might give a peak current of 50A, but it's such a short duration, it doesn't cause any damage.
--- End quote ---
Yes... I was obviously 'remiss' not to 'understand' (which I did), but to 'Include' the obvious 'Time-Factor'. Obviously I was not talking about
the likes of RCD's or ELCB's etc tripping in MilliSeconds, But someone getting hold of such an Earth referenced conductor, without such protection. So to correct
my statement... It is not 'X' number of Volts that is the problem, but 'X' number of milliamps for a specified time! I'm no-one's enemy here!! :)
Siwastaja:
It's also worth understanding
1) Ohm's law
2) The difference between a current source and a voltage source
3) The rarity of true current sources, and the abundance of voltage sources, around us
to see why safety limits are primarily given in voltages, not currents.
Ohm's law connect the two together so it's makes zero sense to argue "which is dangerous", they are different ways to look at the same thing, namely energy transfer. Current and voltage are just tied together, if there is dangerous voltage applied to a human body, there is dangerous current flowing, and vice versa. So you choose current or voltage viewpoint depending on which is the suitable tool for the task. Voltage limitation (of the voltage source), or current limitation (of the current source) ensures safety the easy way - i.e., use Safety Extra Low Voltage - but isn't always an option.
PlainName:
--- Quote ---my statement... It is not 'X' number of Volts that is the problem
--- End quote ---
I don't believe anyone has suggested that's the case. Perhaps you could point out where you think they have, and then we will all have a common base to work from instead of making up our own straw men to then knock over.
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