Posts Tagged ‘earth’

Ground Fault Circuit Interrupters

Sunday, June 26th, 2011
     I’ve been talking about how I was asked to be a subject matter expert for an upcoming series on The Discovery Channel titled Curious and Unusual Deaths.  Most of the accidents discussed involved electrocutions, and in each case the electrocution occurred because the victim’s body, usually their hand, inadvertently contacted a source of current.  When that happened their bodies essentially became like a wire, providing an unintended path for current to travel on its way to the ground.  Why does it travel to the ground, you ask?  Because electric current, by its very nature, always wants to flow along a conductor of electricity from a higher voltage to a lower voltage.  The ground is the lowest voltage area on our planet.  When electricity flows to ground along an unintended path it’s referred to as a “ground fault,” because that’s where the electricity is headed, to the ground, or Earth.  By “fault” I mean that something in an electrical circuit is broken or not right, allowing the electrical current to leak out of the circuit along an unintended path, like through a person’s body.

     For example, in one of the Curious and Unusual Deaths segments I was asked to explain how a fault in wiring caused electrical current to flow through a woman’s body to the ground that she was standing on.  This happened when she unintentionally came in contact with a metal door that was, unbeknownst to her, electrically charged from an unanticipated source.  The current was strong enough to cause her death.  Where did the electric current originate from?  Watch the program to find out, but I’m sure you’d never guess.  To say that it was an unlikely source is an understatement.

     When ground faults pass through a person’s body, bad things often happen, ranging from a stinging shock to stopping your heart muscle to burning you from the inside out.  The severity depends on a number of factors, including the strength of the current to the amount of time your body is exposed to it.  It might surprise you to know that if your skin is wet at the time of contacting a current, you risk a greater chance of injury.  Water, from most sources, contains dissolved minerals, making it a great conductor of electricity.

     But what exactly is electrical current?   Scientifically speaking it’s the rate of flow of electrons through a conductor of electricity.  Let’s take a closer look at a subject close to home, a power cord leading from a wall’s outlet to the electric motor in your kitchen hand mixer.  That power cord contains two wires.  In the electrical world one wire is said to be “hot” while the other is “neutral.”  The mixer whirrs away while you whip up a batch of chocolate frosting because electrons flow into its motor from the outlet through the hot wire, causing the beaters to spin.  The electrons then safely flow back out of the motor to the wall outlet through the neutral wire.  Now normally the number of electrons flowing into the motor through the hot wire will basically equal the number flowing out through the neutral wire, and this is a good thing.  When current flow going in equals current flow going out, we end up enjoying a delicious chocolate cake.

     Since the human body can conduct electricity, serious consequences may result if there is an electrical defect in our hand mixer that creates a ground fault through the operator’s body while they are using it.  In that situation the flow of electrons coming into the mixer from the hot wire will begin to flow through the operator’s body rather than flowing through the neutral wire.  The result is that the number of electrons flowing through the hot wire does not equal the flow of electrons flowing through the neutral wire.  Electrons are leaking out of what should be a closed system, entering the operator’s body instead while on its way to find the ground.

     Next time we’ll look at a handy device called a Ground Fault Circuit Interrupter (GFCI) and how it keeps an eye on the flow of electrons, which in turn keeps us safe from being electrocuted.