Grounding is a method of giving electricity the most effect way to return to ground via the service panel. You see current flows from the panel to the outlet or device to power it up. The neutral wire is the return path for unused current. The ground wire is an additional path for electrical current to return safely to the ground without danger to anyone in the event of a short circuit. In that instant, the short would cause the current to flow through the ground wire, causing a fuse to blow or a circuit breaker to trip.
Ground wires used on power tools, vacuums, and other portable devices are made much safer when they incorporate the use of a third prong, thus a ground connection. Often people do an unthinkable act of cutting off the ground tab of an extension cord or power tool. This usually happens when the outlet being used has no ground, thus a polarized plug.
Dangers of an Ungrounded Appliance
An ungrounded electrical box, appliance, power tool, or extension cord could become a danger if there is no path to ground, except through you. You see, without a ground wire, your body may complete the ground path and you may be shocked or electrocuted. In older homes with cloth wrapped wire or in homes with knob and tube wiring, this is the case. As you know, newer appliances and some tools come equipped with a three-pronged cord, incorporating a ground for protection. Remember, any contact with a metal box, appliance, or electrical panel that has no ground can potentially make you the ground connection, so be extra careful!
Why Proper Grounding Is Important
A properly grounded circuit has boxes, devices, and service panel grounds that give the electrical current the easiest path to ground and that reduces the chances of someone getting a shock or getting electrocuted. Household electrical systems are required by the National Electrical Code to have a grounded system connected to earth ground via a ground rod.
The earth absorbs the over-current or short circuit harmlessly and having done so, eliminates the threat to anyone that may have otherwise been the ground path.
But ground rods and ground wires to boxes, devices, and service panels are not enough. You must remember to bond the grounds to the house’s copper water lines. You certainly wouldn’t want a short circuit to travel through the water pipes while you’re in the shower, bathtub, or using a sink. Remember that water and electricity don’t mix! Likewise, remember other potentially dangerous areas around the home like hot tubs, swimming pools, and spas.
And while we’re on the subject of grounding, we're often asked if using a receptacle adapter is OK. It's better to change the receptacle to a grounded receptacle and have the ground wire connected to the receptacle and the box. Although you can use an adapter and connect the center cover plate screw to the adapter to gain a ground if the box is grounded, it just seems like a skimpy, lazy way to fix the real problem, the need for a new receptacle. Changing the receptacle may be more of a need than a want in many ways. The receptacle may be a regular style now but may require a GFCI in its place due to recent code changes.
One change is that you need GFCI's in basements, garages, and anywhere there is concrete on the floor, including wet areas and outdoors.
Receptacles that have only a hot and neutral slot are called polarized receptacles. By having a smaller hot wire slot and a larger neutral slot on a polarized receptacle, the electrical current flows the appropriate way through the circuit. For safe use of these receptacles, double-insulated power tools can be used in polarized receptacle circuits. These safety features can reduce the risk of electrical shock, but once again, my advice is to replace the receptacle and rewire if needed to convert the circuit into a properly grounded circuit and receptacle.