Electrical Schematic for AC

[babydingbat]

I'm putting on a class for Lockout Energy Control at work and I wanted to start the class off with explaining a little bit of how electricity works. I'm looking for a site that has an AC Electrical Schematic. I took a DC class before, so I understand Ohm's Law (I=V/R), and how the correlation works, but I've never taken AC. For death to occur, the human body must become part of an active electrical circuit having a current capable of overstimulating the nervous system or causing damage to internal organs. I'd like to show them how, with a schematic.

[babydingbat]

Never mind, I found a good one.
http://www.tpub.com/neets/book2/1a.htm

Thank you for trying though!

[Knothead]

For death to occur, the human body must become part of an active electrical circuit having a current capable of overstimulating the nervous system or causing damage to internal organs.

Errr...I think I'll stay over here...

[desmocat]

Also, it might be a good thing to point out that it only takes a very small amount of current,( measured in milliamps) that can cause the heart to stop beating or go into palpatations(irregular beating where no blood is being pumped.) and cause death.
That's why usually if you are working in MCC's (motor control centers) or in drive cabinets, there should be rubber mats on the floor to stand on to help insulate you.

Another rule I was taught was to not have a path that would allow the electricity to go through your heart, for example have a hold of the screwdriver/tool in one hand, and holding onto the cabinet or potential ground point with the other. This would give a current path from one hand, through the chest/heart area and out thru the other arm and hand.
In the steel plant I worked in, we dealt with anything from signal level (5VDC~ 4-20 mA )all the way up to 14,100 volts in the subs that fed the various mill equipment.

Occasionally, we would also have to go into the main switchyard, where the incoming voltage was 138 KV. That made me REEEEEEAL careful.
It was also mandatory to work at least in pairs in the substations and anywhere else that high voltage was present.

I think Doc works in the electrical maintainence field and could probably give a few pointers as well.

[Gomer]

Immersing my fingers in two vials of salt water with 20 volts across it ran 7 mA through my fingers. That was a pretty healthy bite. I believe that is about how much current needs to pass through your chest to kill you.

[Graham]

You could give them a practical demonstration, ask for volunteers.

desmocat, at those voltages it doesn't wait for you to touch it, it comes and gets you!!

One bit of useless information I remember (Guiness Book I think), "lowest voltage to cause death is 12V", and to think we used to grab the bus-bars on the 40,000 Amp hour 50V batteries in the telephone exchanges, gave you a bit of a tingle to say the least, and then there was the ringing current, 75V a.c., oh and Telex, +80V -80V (160V) OUCH!!

Dont try that at home

G

[babydingbat]

Hey thanks guys! Knothead - just stay clear of the windmills out there!
Estimated Effects of 60 Hz AC Currents
1 mA = Barely perceptible
16 mA = Maximum current an average man can grasp & "let go"
20 mA = Paralysis of respiratory muscles
100 mA = Ventricular fibrillation threshold
2 Amps = Cardiac standstill and internal organ damage
15/20 Amps = Common fuse or breaker opens circuit*

Contact with 20 milliamps of current can be fatal. As a frame of reference, a common household circuit breaker may be rated at 15, 20, or 30 amps.

The presence of moisture from environmental conditions such as standing water, wet clothing, high humidity, or perspiration increases the possibility of a low-voltage electricution. The level of current passing through the human body is directly related to the resistance of its path through the body. Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body's resistance to 1,000 Ohms. Meaning that:
Under dry conditions, Current=Volts/Ohms = 120/100,000 = 1 mA, a barely perceptible level of current. Under wet conditions, Current=Volts/Ohms = 120/1,000 = 120 mA, sufficient current to cause ventricular fibrillation.

High-voltage electrical energy quickly breaks down human skin, reducing the human body's resistance to 500 Ohms. Once the skin is punctured, the lowered resistance results in massive current flow.

How does this sound for a start on the class?

[desmocat]

Uhh, that should get their attention! That's what you want.
Start out with the "look how easy it is to get killed" stuff and they should pay attention from then on.

[babydingbat]

Originally posted by desmocat
Uhh, that should get their attention! That's what you want.
Start out with the "look how easy it is to get killed" stuff and they should pay attention from then on.

Thanks desmocat! That's exactly what I want. I don't want to hold a class just telling the people to lock out because it's policy or law. I want people to understand why these policies and laws were put in place to begin with. People seem to get too relaxed in their jobs and even at home, and they tend to start thinking their invinsible or something. That's where I come in to remind them that their not, and we'd like them to be able to go home to their families every day. We go to work "to work" not "to die!"

[CERuppel]

Originally posted by Graham
You could give them a practical demonstration, ask for volunteers.

Hey, I can think of a couple of supervisors that would be great for this...