Electric shock

[colin mac]

I was building a power supply in school. 230V mains was coming into my board and into a 15V transformer, from one of these safe blocks.
**broken link removed**
The teacher didn't give much warning and said it was safe. He put insulatiing
tape over where the live and neutral were coming in so it obviously wasn't a good idea to go near there at least.

Anyway, after I connected the diodes, I was touching the thing and got a jolt that felt like it lasted about a second. I thought wtf, because I thought I was nowhere near the live, but when i turned the board over i realised I never cut the tracks like he said to do the day before so all along the top of the board must have been live. Now, the thing is the shock wasn't that bad, it was bad, but I didn't scream out or anything like that. No one was beside me so no one in the class noticed. Can anyone explain what happened? The fact that the teacher wasn't exactly been careful makes me think I was never going to be killed but at the same time the live was hooked to the board. Did the safe block prevent the current?

 

[Krumlink]

I was building a power supply in school. 230V mains was coming into my board and into a 15V transformer, from one of these safe blocks.
**broken link removed**
The teacher didn't give much warning and said it was safe. He put insulatiing
tape over where the live and neutral were coming in so it obviously wasn't a good idea to go near there at least.

Anyway, after I connected the diodes, I was touching the thing and got a jolt that felt like it lasted about a second. I thought wtf, because I thought I was nowhere near the live, but when i turned the board over i realised I never cut the tracks like he said to do the day before so all along the top of the board must have been live. Now, the thing is the shock wasn't that bad, it was bad, but I didn't scream out or anything like that. No one was beside me so no one in the class noticed. Can anyone explain what happened? The fact that the teacher wasn't exactly been careful makes me think I was never going to be killed but at the same time the live was hooked to the board. Did the safe block prevent the current?

60hZ AC at 230V travels on the skin, and it doesnt actually pierce teh skin. Lucky you. It sounds like it was plugged in

From your description It is a little hard to figure out what happened.

 

[ClydeCrashKop]

You probably touched the live circuit and was grounded through your shoes. Not a very good ground but enough to Zap you. Or, you are like me, electricity turns me on. 115 volts is just annoying, 230 volts stimulates me and I had to go home and chase my wife around.

 

[Krumlink]

You probably touched the live circuit and was grounded through your shoes. Not a very good ground but enough to Zap you. Or, you are like me, electricity turns me on. 115 volts is just annoying, 230 volts stimulates me and I had to go home and chase my wife around.

What happens when you caught her

 

[ClydeCrashKop]

Sparks!

 

[ldanielrosa]

60hZ AC at 230V travels on the skin, and it doesnt actually pierce teh skin. Lucky you. It sounds like it was plugged in

I strongly disagree! If it were safe then people wouldn't die from electrical shock every year. Develop good habits early. Test for _any_ continuity between the mains side and the circuit side. Any detectable current path should have a good explanation. If your teacher says otherwise, just nod but do it _right_.

 

[ClydeCrashKop]

My first car needed body work. My fathers electric sander obviously had a problem because it was shocking me when it was on. Sometimes it got really annoying but I used it for the whole project. (Dumb kid at the time)
I didn’t realize that was less sensitive to electricity than other people until high school auto shop class when the teacher had a magneto with a hand crank. Everyone volunteered, jumped, yelped and let go as soon as he started cranking. Not into playing games, I didn’t volunteer until harassed. I told the teacher, OK if I can do it to you. It felt like a strong electric buzz until I said OK, that’s enough. When I did it to him, he had no reaction either. An ignition magneto has to be in the kilovolt range, right?
PS. I do not stick my finger in light sockets.

 

[Nigel Goodwin]

An ignition magneto has to be in the kilovolt range, right?

In the 10's of kilovolts!.

Where did he find a magneto from?, has he kept it to harrass kids with for the last 50 or 60 years?

We used to have great fun using magneto's off old motorbikes, you don't need a handle to wind it, just a quarter turn 'flick' with the fingers!

We still use a hand would 'Mega' at work to catch any unsuspecting people we can, it has the WWII military logo stamped on it, they put out about 500V.

 

[ClydeCrashKop]

That was about 1970 but I am sure he just had it to harass kids.
I thought of a funny from about 1980. I was a mechanic at a Nissan dealer. One of the porters was harassing the mechanics about being wimpy white boys and bragging that he knew karate. One mechanic said, That’s OK, I know 2x4. I brought him over to the car I was tuning and pulled a plug wire out of the distributor and ran it at idle. They had electronic ignition by then so nice hot sparks. I put my left hand on the valve cover for a good ground and held an air blower nozzle tight in my right hand to avoid spark burns. I swear the sparks jumped 2 inches or more when I held the nozzle near the distributor and my arm jumped at least that much. After about 10 hits in a row, I offered him the blower nozzle and he ran like a scalded dog.

 

[Hero999]

60hZ AC at 230V travels on the skin, and it doesnt actually pierce teh skin. Lucky you. It sounds like it was plugged in

From your description It is a little hard to figure out what happened.

That's not true, 50/60Hz is too low for the skin effect to take place and human flesh isnt conductive enough even at tesla coil frequencies for the skin effect to protect you - it's all a myth.

I can think of two possibilities;

Some of the mains was capacitively leaking from the primary to the secondary.

You had very moist and sweaty fingers. Voltages as low as 12VAC or 30VDC can shock you if your hands are damp which is why the IEE regulations state that installations in wet environments should be insulated from the user if the voltage exceeds this range.

 

[bloke_man]

If your power supply is switch mode you would have some hefty caps on board, even with mains disconnected they can hold a significant charge for long periods. Many of us sometimes forget this and rush into repair work only to receive a blast from any remaining charge.

Been caught a few times myself, occasionally glow in the dark!

 

[Centretek]

230V is lethal when current flows through your chest. From one finger to another on the one hand will kick you but as little as 1mA through your chest will cause you heart to go into fibrillation which will require CPR to save you. If the current is above 2 Amps your are stone dead and beyond any hope as it burns out the nerve paths in the heart muscle.
(Level III First Aid Course).

Your teacher was not being cautious enough and YOU stuffed up by not doing it properly like you were told to.
Count your blessings for a lucky escape AND LEARN FROM IT!!!

 

[NSKL]

As far as I know, moisture has A LOT to do with this. If your hands are wet/sweaty the skin resistance is drastically reduced and you are more prone to getting shocked. Under special circumstances very low currents and modest voltages (12V) might kill you if current runs through your chest. Good habit is to always hold one hand in your pocket when working with "potentially dangerous" currents/voltages since this way current will run through your body to your feet, but not across your chest.
-Igor