Thread: For the scientifically minded...

Before becoming a barber I was an wiremen for 15 years so here goes.

A.C. or alternating current- basically the electrons are Vibrating back and forth.
D.C. Or direct current is more like a Jacobs ladder.

If you choose to think of it as water,
Voltage is the size of pipe
Current or amperage is the pressure of the water.

Voltage isn't what kills you, amperage is, it only takes .5 amps to stop the human heart.

Without too much detail if you don't give electricity a path it won't shock you, so if your wearing rubber soled shoes and grab a hot wire and nothing else you won't feel a thing because there is no potential.

Yes I have been shocked many times and been very lucky 120v, 240v, 277v and 480v by far the most painful was the 277v, ugh I still cringe when I think about it.

Another ironworker memory ..... guy I knew .... they were at the power house at Turkey Point in Homestead, FL... 40 years ago or so. Had to take an I-beam from one location to another and were using a 'cherry picker'' which is a relatively small capacity hydraulic crane with a telescoping boom, to carry the beam.

The guy is walking with one hand on the end of the I-beam to control it so it doesn't begin to swing and hit the crane, what have you. As they were turning a corner, the operator turning as the crane is moving and swinging the boom at the same time, he came too close to some high tension electrical wires.

The current jumped to the boom and went into the ironworker's hand, through the I-beam and out his toes. Blew out his toes and the bottom of his foot in places. He was knocked off his feet and fortunately lived to tell the tale. I knew another ironworker who was on a slab doing reinforcing steel who was killed when a piece of rebar got too close to electrical wires but that is a long story.

It only takes 6mA, that's 0.006 Amps to stop your heart, not 0.5A (500mA) Medical grade earth leakage devices operate at 10mA or lower for this reason. Domestic ones typically operate at 30mA.

It's normal to use the analogy of the size of the pipe as being like circuit resistance because it's what restricts flow and the line pressure as being like voltage.

Personal best shock voltage, 45kV. Worst injury, lost the surface of both eyes (and the skin off the back of my right hand) to flash burn. Picture of right eye available on request. Think twice before requesting.

Originally Posted by detroyt

it only takes .5 amps to stop the human heart.

Originally Posted by MickRussell

It only takes 6mA, that's 0.006 Amps to stop your heart, not 0.5A (500mA)

I have experimented a lot with pacemakers. (not always the smartest experiments, but sometimes you just need to know... Besides, emergency personnel were standing by!)
The energy required to cause ventricular contraction with a transcutaneous (through the skin) pacemaker is usually over 50 mA. That is causing depolarization of the muscle, but not enough that it is prevented from repolarizing normally.
When I put pacing patches on my arm and crank it up, it starts to sting at about 20 mA.
I can't even feel the output of an intracardiac pacer (leads go directly to the heart) by setting my fingers directly on the leads and setting the output to maximum. I am not sure what the implanted units output, but I know it's substantially less than a transcutanous unit.

So, in your figures, maybe one of you got information about energy applied to the body and the other about it applied directly to the heart.


After all of that... I don't work with electricity, but shouldn't watts be the important measurement?

Yes, I'm referring to the current needed directly through the heart, not through your skin. I thought I said that in my initial post. Watts, isn't really very helpful in this case as the amount of voltage required to get current to flow through wet tissue is very small while much more voltage (relatively speaking) is required to initiate current flow through dry skin. The human body can handle a surprising amount of power (watts) so long the current path doesn't significantly involve the heart or associated nerve structures.

Originally Posted by MickRussell

Yes, I'm referring to the current needed directly through the heart, not through your skin. I thought I said that in my initial post. Watts, isn't really very helpful in this case as the amount of voltage required to get current to flow through wet tissue is very small while much more voltage (relatively speaking) is required to initiate current flow through dry skin. The human body can handle a surprising amount of power (watts) so long the current path doesn't significantly involve the heart or associated nerve structures.

Watt?????????????????????

Originally Posted by holli4pirating

Watt?????????????????????

When I was seriously into power lifting I saw a book by some guy (read idiot) about "Power factor Training". I left the library very confused as to why someone would want to train the cosine of their phase angle.

Watt is the unit for power, i.e. the rate of energy being dissipated. It depends exactly how is that energy dissipated. It's just the voltage multiplied by the current (or using ohm's law any other combination with the resistance), so if you know the property of the material at hand i.e. the resistance, generally you can work out what the distribution of current through it and what energy will be dissipated in different parts, when a given volgage is applied.
But as MickRussell said, it's fairly complicated problem for a human body.

Originally Posted by MickRussell

When I was seriously into power lifting I saw a book by some guy (read idiot) about "Power factor Training". I left the library very confused as to why someone would want to train the cosine of their phase angle.

Wow Mick,

Do "nerd" or "dweeb" get used in Australian English?

I apply the term admiringly, as I assume others apply it to me.

I'm just starting my electrical career (4 years in at age 46). Scary stories by you. Sorry to hear of the trouble you had, man.

Most nerds don't train for power lifting meets, eat what they kill, line up to fight forest wildfires and scare the living shyte out of their teenage son's metal-head friends, but it still applies in my case.