AFN                Electric Shock                  Posted 05 October 2006

Quite simply, electric shock is the sensation one feels when an electric current passes through the body.  Whether the shock causes injury or not, depends on the strength of the current that flows through the body.  A very small current can pass through the body unnoticed.  As the current increases, a slight tingle grows to a severe tingle.  A high current is very unpleasant indeed.  Alternating current (AC) and direct current (DC) have somewhat different effects, but both can be dangerous.

If a current flows through the heart muscle, it may cause fibrillation, and that is the classical way of "being electrocuted".  Fibrillation is an uncontrolled flutter of the heart muscle, and this may cause physical damage to that muscle.  If the damage is sufficient, the heart simply ceases to pump blood  --  and you die!

There are other possible ways of death by electrical means, such as having a current of sufficient strength that it fries the flesh, and that, of course, may cause death depending on where the damage occurs.

I have never heard of it happening, but an electric current of sufficient strength through the brain would cause damage, and probable death.   I think that accidental connection with a live wire to the head is a very rare occurrence, so no cases have been recorded of death by that means.  Also, bone is not a good conductor.  The most common method of injury is having a current pass through the trunk with enough of that current passing through the heart to cause fibrillation of the heart muscle.

It is advisable to urgently attend an A&E department of a hospital if a person has just suffered a SEVERE electric shock.  Cases have been know for a person to be recovering from a severe shock and just drop dead.  The injury to the heart muscle did not cause immediate heart failure.  An electrocardiogram will tell a trained medic if damage has occurred to the heart.

 Very small currents may not be felt, and generally will not cause any ill-effects.

I am not going to consider very high frequency currents, as these obey rather different laws to normal DC and low-frequency currents.  Most people only have dealings with normal 50 or 60 Hertz mains-supply currents.  It is these that I am going to consider.

Electric current consists of sub-atomic particles travelling through a conductor.  A lot of things are electrical conductors, including the human body.  The body is not a good conductor when compared with most metals, but blood is salty water (plus a few other things) and is quite good enough  to conduct enough current to cause fibrillation.  Of the various metals, silver is the best, with copper and aluminium coming up close behind.

Electric current is what actually goes THROUGH a conductor.  Newspaper reports such as "he had 30,000 volts go through him" are pure drivel.  Voltage is the force that drives current through a conductor.  30,00 volts will drive a lot of current through the resistance of the body.  This is the reason why it is a good idea to stay away from high voltages.  The current may not cause fibrillation, but it may fry or char human flesh.  Fools that climb power pylons are often not electrocuted, they are either burned to death, or fall on to very hard ground.

A little bit about how electric power is supplied to houses.  This will let you see where the dangers lie.  For an electric current to flow, there must be a circuit.  A circuit is a ring, the current must return to the point from which it started.

At the end of the road there will probably be a sub-station.  This is where very high voltage currents arrive from the power station.  I won't go into the nitty-gritty complicated details of the actual wiring, I'll simplify the story, but keep the general principles true.  At the sub-station there will be a transformer that brings the high voltage down to (generally) 240V.  There will be two wires from the transformer to your main fuse box.  As I said, you must have a path that allows the current to return to where it started.  At the transformer end, one of those wires is connected to a heavy plate sunk into the ground so that it connects to the body of the earth.  It may be cast iron, it may be copper, but it will make a good electrical contact with the body of the earth  --  generally via the water table.

The wire that is NOT connected to the earth (or 'ground' as they say in the USA) will be known as the "line" or "live" conductor.  The other wire will be known as "the neutral". So at the house you can get a shock between either line and neutral or line and earth.  The reason for this method is a bit complicated because I have not told the whole story of how the transformers work.  You will just have to take my word that there is a very good reason for this method.  (If a reader is really interested, I will explain further by way of an email, but it would confuse most folk to be told the whole story) cdcnottm@aol.com

Touching the live wire is quite safe ALWAYS PROVIDED that you are not connected to earth.  And this requirement is not as simple as it sounds.  There are earthed tings all around you, and under your feet.  Normal leather shoes standing on seemingly dry concrete, may give you a connection to earth.  It won't be a good connection, but it may well be enough to give you a shock.  Five thousandths of am amp (5milliamps) is enough to know you are being shocked.  50 milliamps is enough to kill you.

If you see an electrician working with one hand in his pocket, you will know that he is probably working on a live cable.  He will have checked that what he is standing on insulated him from earth.  It is so easy to forget that you are working on a live conductor, that you can just use the other hand without thinking.  If the two hands connect to live and earth (or live and neutral), 240v across the chest can be lethal.

Have a look at paragraph 29 of page AEA to see one of the dangers relating to most electrical supplies having one side earthed.  This para gives some safety advice too.