Electrical Grounding


In response to a question I received during a home inspection, I’ve tried to supply a little more detail to the safety aspects of electrical grounding in your home.

Most of us who have lived in a home built prior to the mid 60’s will remember the outlet pictured here on the left.  It is the familiar electrical interface from which the marvels of home appliances were made to work.

In its earliest conception the two slots were equal in width and an appliance could be plugged in without regard to alignment.

outlet

Outlets:  The outlet on the left, shown here, represents a later revision that is ‘polarized.’  Which is to say merely that the mating prongs (also of different widths) would fit into the outlet only one way.  The electrical potential available through either opening and ground (meaning you) is and can be, however, lethal.

This drawback led to the development of the contemporary outlet, pictured on the right which has a third connection.  This is the ground wire, which is inert until needed and is a safety feature to prevent electrocution should the appliance be electrically damaged.  Just consider how much easier it is for electricity to use this connection than to go through you should there be a problem.

The term 'ground' here refers to an actual physical, electrical connection to the earth.  This connection is made with either a dedicated copper rod driven into the ground outside your house or more commonly your copper water supply pipes which run into the ground outside your house.  The earth ground is a viable return path for electricity simply because of its almost infinite size and as demonstrated by Benjamin Franklin (is that a true story) and the kite it is the path sought by electric charges during a lightning storm.

The larger slot in both the polarized and grounded outlets shown here is the ‘neutral’ connection. This is a convention and term that has arisen from the fact that this leg of the circuit is  electrically connected (bonded) to the ground wire back at the service panel. 

panelGrounds:  Note in this illustration that the white wires are neutral and the uninsulated copper wires are the grounds for their respective circuits.  Hence the term ‘neutral,’ the white wire / wide slot on the receptacle no longer represents an electrical potential to ground when properly wired.

Only one wire left, the ‘hot’ wire. As discussed above we can see that in early non-polarized and ungrounded electrical wiring both ‘legs’ of the electrical circuit were potentially hot. Which is to say that if you inadvertently became the ground for either leg, an electrical potential (voltage) would be present with possible lethal consequences. In these older systems it is not uncommon to find both wires are black.
 

The modern convention identifies the hot wire as black and it is isolated in lamps and appliances by always being the fused wire. The first layer of isolation occurs at the breaker panel where it can be turned on or off or tripped automatically by a circuit overload. Subsequent isolation is achieved by the wall switch or appliance switches whch always connect and disconnect this wire.

All that’s is fine and well, you say, so why should I be concerned?  As with any human endeavor, though unintentional, mistakes and omissions can and do occur.  The appliance or device will not care if the ground is missing or the outlet polarity is reversed.  This safety feature, built in by design, will not be missed by you until you need it.

reversePolarity:  If the hot (black) wire and the neutral (white) wire are mistakenly wired to the wrong connection at the outlet, the appliance, device lamp or what have you will still operate, but the neutral wire will now be the switched (and fused) leg of the circuit the hot wire is now always energized inside the device thereby increasing the potential risk even when the device is off.

In the illustration below you can clearly see the hazard created by a lamp with reversed polarity, simply because the threaded portion of the socket (most easily touched when changing a bulb) is now always hot.  The only safe way to change the bulb under this condition is to unplug the lamp.Not always possible  if the outlet is behind large furniture or the fixture is directly wired.

light


The wire colors have been changed in the illustration to the left for clarity but clearly shows the danger.  You may think the lamp wiring is bad should you be shocked while changing a bulb.   Dissassembly and inspection of the lamp reveals nothing, however, because  the problem exists in the outlet wiring.


Despite every attempt to minimize the danger, electrocution still remains a common residential safety problem.

Ground Fault Circuit Interrupter (GFCI):

GFCI's were developed in the ‘70’s and phased into electrical code over the ensuing years.

gfciBasically a circuit breaker built into an outlet (also available as a circuit breaker) its function is to instantly break the flow of current when a sudden change in current flow occurs.

The best description of this would be when you stick that fork into the toaster to retrieve the toast (please, don’t actually do this). The GFCI will not eliminate a shock but will reduce the risk of serious injury by the speed (1/40th of a second) with which it can disconnect the circuit.

GFCI’s are commonly located in areas with close proximity to water or plumbing; bathrooms, kitchens, laundry, spas and outdoors. This is the location where you are most likely  to become (by direct contact) a better ground than the safety grounding wired into the outlet.

 GFCI's are easily identified by their ‘Test’ and ‘Reset’ buttons and should be tested regularly to insure their continued operation.

Arc Fault Circuit Interrupters (AFCI):

The most recent addition to the electrical safety arsenal has been the introduction of Arc Fault Circuit Interrupters (AFCI). Like GFCI’s they also have a test button, but unlike them AFCI’s are only available as circuit breakers and offer protection through-out the circuit to which they are installed.

afci

Pictured here the AFCI breaker contains a small electronic circuit inside which senses the fluctuations of current (spikes) associated with arcing caused by loose or poorly made connections (a common source of electrical fires).  The white wire coiled beneath each of these breakers is actually a neutral connection to power the internal circuitry.

 * * * *  

I hope this page has helped you to visualize the importance of electrical safety in your home and how these devices work together.  The more advanced reader will be quick to point out the simplicity of this presentation, but it has not been my intent, nor am I capable, to make either of us an  electrician, simply to inform.


Independent Home Inspection routinely checks these items during your home inspection to insure the safety of you and your family.


Resources

CPSC
Documents:

Electrical Safety in the Home

Ground Fault Circuit Interrupters

Arc Fault Circuit Interrupters

Electric Heaters

Smoke Alarms

Where to put Smoke Alarms

Vocabulary

Ampere (Amp.): The measure of current flowing through a wire.

Circuit Breaker: These protect against power surges or power drains caused by malfunctioning equipment. Circuit breakers and fuses are comparable except that circuit breakers can be reset instead of replaced.

Extension Cord: This extended wiring should be used only temporarily and for only one appliance at a time. The rating on the cord should be of equal or greater wattage than the appliance.

Fuse: These protect against power surges or power drains caused by malfunctioning equipment. Fuses and circuit breakers are comparable except that fuses must be replaced instead of reset.

GFCI: Ground Fault Circuit Interrupter. Used to prevent electrocutions when electricity is being used near water. Detects when significantly more electricity is going out than is coming back in and cuts off power as a result. Can be bought for panel boxes or individual outlets or switch/outlet combinations.

Horsepower (h.p.): A unit equal to 746 watts. Usually used to measure the power of motors.

Kilowatt (kW): 1,000 watts

Kilowatt Hour (kWh): A unit of work or energy equal to using 1,000 watts for one hour. Your bill is computed according to the number of kWhs that you use.

Megawatt (MW): 1,000 kilowatts or 1 million watts

Outlet: Individual places to plug in appliances. Beware of overloading outlets and extension cords.

Plug, Polarized: A plug with one prong that is larger than the other. This means you will be forced to insert it the right way, which prevents shocks.

Plug, Three-Pring: A plug that has three prongs: two normal ones and one for the ground. A ground keeps you and your appliance safe from electricity that is leaking.

Voltage (Volt): The force which moves electric current through a conductor from the origin to the point of use.

Watt (W): A basic unit of electrical power used for measuring the rate of work done.  W=V/A


































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