I had an ELECTRIFYING weekend!

[keith]

I've had a few 120V's and one 240V shock. The 120V was like a tickle compared to the 240V. Very nasty indeed.

Here's a funny story. A friend worked in a telephone exchange, back when they were full of power hungry Strowger style mechanical switches. The exchange had it's own substation, and something a little over 10KV came into the building. There was one big test point to see if the circuit is live. The routine was this - put on rubber boots, rubber gloves, stand on a rubber mat, hold a 4 foot long bakelite rod with a neon bulb on the tip. If the bulb lit up when touching the test point, the circuit is live. Enough current flowed through the rod, you, and the rubber to light the bulb.

Next to the test point, there was a first aid kit. Inside the first aid kit, nothing but a dustpan and brush. Think about it - if you make a mistake, you will be fried.

I get nervous around 110V. Forget about a job like that.

 

[TallPaul]

quote:

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It ain't the volts that getcha, it's the amps.

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Maybe or generally. But what about a car battery: 12 volts and 500 amps or more, yet we never hear about people being electrocuted by a car battery, though I believe it can do it. Apparently there is not enough pressure (voltage) to push all the amps through the somewhat resistant human body. OTOH, a static shock is said to be 10,000 volts, but an infintesimally small amperage.

 

[tdi-rick]

the standard single phase supply voltage here is 240V/50Hz, with the three phase stuff 415V.
Having worked with it most of my working life and been bitten a few too many times, you have a fair respect for it.

One of my mates used to work on the railways here as a line tech. Big voltages, DC current. He's also been knocked off poles a few times by lightning. On those occaisons the warning call would come through to abandon the job (as lightning was in the area) after one of the nearby towers/poles had been hit.

All the internal fencing on the inlaws 1700 acre cattle property I used to run was all electric. In favourable conditions it would exceed 9000 volts. You really know when you get a belt from that when being a little careless.

 

[Shaman]

We had an electric fence at my grandma’s house. As kids we would all lock hands and grab ahold.

 

[Bob Woods]

If you assume the human body to have 100 ohms of resistance, 100 volts applied to it will create a one amp current flow, double the voltage and you double the current flow.

 

[Pete C.]

Double the voltage and you reduce the amperage by 1/2. Read the nomenclature label any dual voltage device.

 

[TallPaul]

quote:

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Double the voltage and you reduce the amperage by 1/2.

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As in watts = amps times volts

But maybe he was not holding watts constant?

 

[Bob Woods]

Pete, I'm not referring to device ratings, just ohms law, one volt applied to a one ohm device will flow one amp of current disapating one watt or one volt/amp.

http://www.the12volt.com/ohm/ohmslaw.asp

 

[brianl703]

Most (if not all) of those dual-voltage devices have regulated, switch-mode (aka switching) power supplies. That is why they show that doubling the voltage reduces the amperage: The circuitry in the power supply automatically adjusts itself for the additional voltage and therefore draws less current.

A simple resistive load will indeed draw double the current when double the voltage is applied.

A switch-mode power supply is not a simple resistive load.

 

[kanling]

Current is reduced by half when voltage is doubled only for devices that operate at a fixed power level. (P=VI) Complex dual voltage devices do, because their power supplies are designed to supply the required power regardless of the input.

For a simple resistance, (I=V/R, Ohms law) doubling voltage will double the current. And this actually means that the power (with voltage doubled) goes up four times!

 

[brianl703]

That is also why a bridged audio amplifier (common in the car-audio world) gives you quadruple the power--because bridging the amplifier doubles the voltage applied to the speaker.

 

[Alan]

I've been hit with 277ac and 420dc.It's nasty stuff.

 

[Bob Woods]

I spent years working on medical xray, on systems with up to 150,000 volts at 1 amp, I was lucky and never got hit with anything higher than 120AC and 135DC.

 

[ekpolk]

By way of morbid comparison (as if this thread isn't morbid enough already...), while every state was a little different, a typical electric chair system would start off briefly at 2000v and 4 amps (to get a good path established), and then quickly shift to 500v and 8 amps, and then shift between those extremes a couple times for couple of minutes the thing was "operating." It may not have been much fun for those who had to clean up afterwards, but I have a hard time believing that anyone suffered at all taking that sort of current straight into their brain.

So, who's going to start the "I had a LETHALLY INJECTED weekend!" thread???

Back on topic a bit -- I think that the hertz rate also has some to do with the "quality" of the electrocution experience. I once got a quick shot of 400 hz AC off one of our aircraft that was being worked on (incorrectly, I hasten to add...). It's hard to verbalize, but it seemed much "zingier" than the "mere" 110v 60hz shocks I've had before.

 

[TallPaul]

Yeah, the human body is a resistor, like a toaster. Instead of overloading the circuit and blowing the fuse, it will think you are the toaster and keep heating you up.

 

[XS650]

quote:

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Originally posted by 1sttruck:
Don't some old timey electricians test for hot 120V by licking their fingers and then quickly touching the suspect wire ?

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The don't lick thir fingers, no need to do that. You'll feel 120V with dry fingers just fine

My dad used to check for power that way. There's a bit of a science to it. Just a light tap with your hand moving so intertia will take it away from the wire and so that if you get a good connection and your hand closes, it won't be gripping the live circuit.

 

[Thermactor]

The Smiths were proud of their family tradition. Their ancestors had come to America on the Mayflower. They had included Senators and Wall Street wizards.

They decided to compile a family history, a legacy for their children and grandchildren. They hired a fine author. Only one problem arose - how to handle that great-uncle George, who was executed in the electric chair.

The author said he could handle the story tactfully.

The book appeared. It said "Great-uncle George occupied a chair of applied electronics at an important government institution, was attached to his position by the strongest of ties, and his death came as a great shock."

 

[tom slick]

I zapped myself with 277 one time, that was alot of fun! luckily i just bumped it with the back side of my hand and it only when through my hand as it grounded to the enclosure.


for those unfamiliar with 277 it's one leg of 480 three phase.

BW is correct with the voltage-amps. power consumption goes down in a device but the potential power from the source goes up.

 

[9c1]

I spent 33 years with an electric utility switching on voltages from 120v to 765Kv. Even ran railway converters AC to DC -- 600v & 1500V DC. Never hurt anyone or myself, but I worked with a lot of guys who had very bad burns, and some have serious disfigurement. My hero blew a 1 amp fuse at 12Kv with his body, and lived to talk about it. He owes his life to the quality of that fuse. He has very bad austio-arthritis today, but he is enjoying his retirement. A few of our colleagues are not so fortunate. I could tell you some stories..... but it would bore you. I can tell you for sure ... Darwin WAS right.
Electricity deserves respect. Please don’t play with it if you don’t know what you are doing.
Terry

 

[labman]

Got into the 480 ar work once. Actually 277 to ground. If the concrete floor wasn't dry for a change, I may not have been here.