a 220 to 110V thought..some comments please?

[R.G.]

Why not try a variac?

A variac is a bigger, heavier, more flexible version of a 220-to-110 autotransformer.

[drk]

kinda offtopic, but in one guitar, i took the wire that connects the bridge(and consequently the strings) from the circuit because of that potencial problem, though it ended up a bit noisier(the guitar)
is this a good way to prevent that or there is a better way?

[Jered]

Been shocked by 110 more times than I'd like to admit, but its not that bad. Instinct tells you to pull away and its done.

Let me add a bit more caution to this. The reason it was "not that bad" was that you only made a high resistance connection to it. The amount of current needed to stop your heart is shockingly (sorry - I had to!  ) small. Twenty milliamperes through the chest and you're history. Dry skin brushing against a smooth, dry metal surface can let through only enough to be bad.

If the skin isn't dry, metal has a sharp or rough surface to get past the dead skin layer, or you happen to be where your muscles contracting pulls you INTO the metal, not making you jump away, the current gets much bigger. The "instinct" you mention is your muscles firing from the electricity going through them, not from your nerves firing them. You have zero control of that, as it's not your nerves making the signals and your nerves can't cancel that out. If you happen to have grasped your hand around the charged metal and your other hand's or foot's response to the current is to press into the return path, there is nothing you can do. The current's going to hold you there and cook you. In this case, unless someone else can stop the current, you're dead.

A truly deadly situation happens on stage when a guitarist holds the grounded strings of a guitar with one hand and grabs a "grounded" microphone with the other. He (or she) is usually hot and sweaty, so the skin is wet and its resistance is low. The hands are folded around the metal objects. And if either the amp or the PA has a ground lift and a bit of AC leakage, it's all over. Or if a guitarist has a leaky amp and is standing on a wet grounded surface. Exactly these situations have happened. Dying at a workbench is also common, it just doesn't make the news.

There isn't any shock that is "not that bad". Except for static electricity zaps where the energy is low, they are mostly all potentially (sorry again) deadly.

  I've never been connected with both hands, usually just a brush against a wire in a junction box with the 110. The 220 I was wrapping the wire with electrical tape and my finger found a nick in the wire insulation. It something I'll never forget.

[runmikeyrun]

Our heart monitors on the ambulance have a feature that allows you to electrically pace a slow heart.  You take two sticky pads and place one on the front of the chest and one on the back.  You then set the monitor to pulse electricity through the pads at a set rate, which passes the current through the heart.  It's kind of neat, you start with the current at 10ma and slowly increase it until it "captures", that is the heart starts to beat from the current being passed through it.  I'm not sure what voltage it operates at, but most hearts capture at around 70-80ma.  We try to sedate people first, but it is definitely something that people complain about when not sedated!  You can watch the pectoral muscles twitch every time it fires. 

The other measure of electricity we use is joules- people are defibrillated at 360 joules, but abnormally fast beats are shocked with as little as 50 joules.  You get a zap of either monophasic or biphasic energy across the heart to (hopefully) reset the heart's internal pacemaker to a regular beat.  Unfortunately for us electronics hobbyists it also works in reverse- a good zap can send the heart into a potentially fatal rhythm- too fast or too slow in one section or another of the heart. 

The closest thing you can convert joules to is foot pounds, and 360 joules = 265 foot pounds, which is why the first step in a witnessed cardiac arrest was to literally pound someone with a closed fist in the center of the chest (precordial thump).  It was supposed to perform a similar function to the electricity.  Thankfully we don't do that anymore, it does seem a bit barbaric but was standard practice up until a few years ago.  This was only if there was not a defibrillator handy.  I bet that there's some footage of this on youtube, someone needs to do a search.

I really enjoyed learning about all that stuff in paramedic school... imagine my excitement when i realized that a heart monitor was basically an oscilloscope!

[Jered]

  Sorry Daniel, didn't mean to hi-jack your thread. My bad.

[dschwartz]

  Sorry Daniel, didn't mean to hi-jack your thread. My bad.

by no means be sorry..this thread has become incredibly useful and interesting!!!!!!!

that defribrilator post was just what i like to read on the forum..knowledge is knowledge...

[brett]

I can't believe I'm reading this stuff.
It's like we are living in third world countries.

Like the man said:

use a ground fault circuit interrupter on your gear

One day the power went out while I was playing.  Thinking that I'd blown the output valves (again) I went to make a cup of coffee.  There in the kitchen were my kids (aged about 8 and 13) with a metal knife, trying to extract some toast from the toaster.

Are you or your kids worth $20?
Ground fault/earth leakage devices are the best, cheapest investment you'll ever make (equal to smoke detectors).

For those that already know this, apologies for the lecture.  For the rest, your choice is to learn the easy way or learn the hard way.

[Zben3129]

Ground fault/earth leakage devices are the best, cheapest investment you'll ever make (equal to smoke detectors).

Please use carbon monoxide alarms too, trust me, they are worth it.


Zach

[Jered]

I can't believe I'm reading this stuff.
It's like we are living in third world countries.

Like the man said:

use a ground fault circuit interrupter on your gear

One day the power went out while I was playing.  Thinking that I'd blown the output valves (again) I went to make a cup of coffee.  There in the kitchen were my kids (aged about 8 and 13) with a metal knife, trying to extract some toast from the toaster.

Are you or your kids worth $20?
Ground fault/earth leakage devices are the best, cheapest investment you'll ever make (equal to smoke detectors).

For those that already know this, apologies for the lecture.  For the rest, your choice is to learn the easy way or learn the hard way.

  Here in CA its the law that any receptacle within 8 ft of a water source has to be GFCI protected. Most people don't bother with it until they try to sell the house. Older houses can be a bitch because there is no ground except cold water pipes. Houses built in the 70's sometimes have aluminum wiring. Another nightmare if you want to sell your house.

[dschwartz]

What´s a GFCI? never heard of them....

[R.G.]

Ground Fault Current Interruptor.

An outlet or breaker which looks for either the presence of current on the safety ground wire or a difference in current between the line and neutral wires. In either case, there is current in the circuit which goes in through the line wire and out by either the ground wire or simply leaks out of the circuit. Both are conditions in which the leak could be through a human chest, and so the monitor circuit opens the circuit within milliseconds to protect the hypothetical human.

[Zben3129]

All hair dryers are equipped with these nowadays, for example.

[Paul Perry (Frostwave)]

The problem with a variac is that it is 1. expensive, and 2. gives you (or someone else) the opportunity to set it to any voltage - including a lot of wrong ones!