Posts Tagged ‘ground fault’

GFCI Outlets and The Mighty Robot

Sunday, July 3rd, 2011
     Most people aren’t aware of just how important those strange looking wall outlets in our kitchens and bathrooms are, you know, the ones with the little buttons that say Test and Reset.  They’re known as GFCI outlets, that is Ground Fault Circuit Interrupters, and given the right set of circumstances they could save your life.

     The GFCI equipped wall outlet, like a mighty robot, continuously watches the flow of electrons (electrical current) passing through, always on the lookout for incongruities between the hot and neutral wires, and ready to jump into action when necessary.  Say, for example, that one of these GFCI equipped outlets has an appliance plugged into it. While the appliance is in safe use there is nothing for the GFCI robot to do.  It simply takes note of the balance of electrons flowing between the hot and neutral conductors, notes that they are equal, and continues to watch for inequalities. 

 Figure 1 – While the Hand Mixer is Operating Normally, in the GFCI Outlet the Electric Current Flowing in the Hot and Neutral Wires is Equal.   The Robot Takes No Action. 

     But suppose that there is a problem with the appliance, something that causes a ground fault where the user’s body provides an unintended path to errant electrons flowing from the hot side of the wall outlet.  Those errant electrons are supposed to traverse the neutral wire back through the wall outlet from whence they came, but they have become unruly.  Not to worry, if you are up to code and have an ever vigilant GFCI on that outlet, the robot will immediately notice the anomaly. 

Figure 2 – If a Ground Fault Develops in the Hand Mixer and Some Electric Current Flows Through the User’s Body, Then the Robot Notices a Difference In Current Flowing Through the Hot and Neutral Wires in the GFCI Outlet.

     The Mighty Robot of the GFCI doesn’t like the fact that the electrons are out of balance, that there are more of them flowing through the hot wire than returning through the outlet via the neutral wire, so within a fraction of a second it will jump into action to correct things.  It hits a lever on a spring loaded mechanism that snaps open an electrical switch connecting the appliance to the hot and neutral sides of the outlet, effectively cutting off the flow of electrons to the appliance.  Cut off from power, the appliance ceases to function, but more importantly, the flow of electrons through the user’s body has been stopped before their body incurs injury, or death.

Figure 3- In Response to the Ground Fault, the Robot Opens a Switch in the GFCI Outlet to Cut Off The Flow of Electricity to the Hand Mixer.  The Person Operating the Hand Mixer is Saved.

     The GFCI robot, having done its job, now goes into a sleep mode.  It will be reactivated, ready again for its vigilant watch of errant electrons, when the faulty appliance is unplugged and the Reset button is pressed.  This button does what it says, it resets the spring loaded mechanism in the wall outlet, closing the electrical switch, and making the outlet functional again.  The GFCI robot immediately goes back into active monitoring mode.

   Now it should be noted that as dependable as GFCI outlets are, they can become defective.  That’s why they have a Test button.  This button should be pressed periodically to see if the robot is still on the job.  If all is in order, the Reset button pops out of the outlet, and anything plugged into that outlet will not operate. When you press the Reset button back in, everything should operate again if there are no fault conditions.

     Could the GFCI’s Mighty Robot have prevented the unfortunate incidents discussed during my tenure on The Discovery Channel?  Stay tuned to find out…

     That’s it for GFCI outlets.  Next time we’ll take a look at how an invention developed to defend the allies during World War II later morphed into a space age device that cooks our food. 


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.