Electricity follows the path of least resistance, usually the hot and neutral wires.
When a neutral wire is broken or cannot provide an easy path for electricity to return “home” on, or when a hot wire comes loose, the electrical charge in the hot wire seeks an alternative path to complete its circuit.
Because the earth itself will complete the circuit, the charge will jump through anything that touches the ground.
This is dangerous. The hot wire may cause persistent sparking, or it may be dangerously idle, waiting for a path to discharge.
The job of the grounding system is to provide that path, diverting the charge to the ground so quickly that the sudden surge in the wires causes the circuit breaker to overload and trip. Ground wires accompany all hot and neutral wires and must be connected to every receptacle, switch, fixture, and appliance.
These wires converge at the ground bus bar, which is connected to the ground by a No. 6 or larger wire. The critical link in the entire system is the connection of this wire to the ground itself.
A cold water pipe used to be sufficient, but plastic plumbing materials now make it necessary to augment this connection with at least one grounding electrode connector.
See also: What To Do During A Power Outage
Many local codes require that the ground wire continue uninterrupted to a second ground, such as an additional rod or cold water pipe.
There are four ways in which to ground your system:
1. Buried. Connect the ground wire coming from the service panel to No. 2 or larger copper wire buried 2 1/2-feet deep for 20 or more feet along the house.
2. Attached to pipe. Slip large ground wires into a clamp connected to a metal cold-water pipe. A bonding jumper may be required at the water meter.
3. Attached to rebar. Connect the ground wire from the service panel to 20 feet or more of 1/2-inch steel rebar or No. 4 or larger solid copper wire enclosed in concrete, usually the foundation of the house.
4. Ground rod. Connect the ground wire to an approved copper or copper-clad ground rod driven to a depth required by local code.
About Electrical Surges
Surges (sudden increases in power) can destroy the microprocessors used in microwave ovens, refrigerators, ranges, personal computers, and televisions.
Surges are produced by changes in power transmission through the lines, electric motors switching on in the house, and lightning strikes on telephone or power lines.
Surges happen so quickly they may not be noticed, but even small ones have a cumulative effect.
Protection from small surges can be accomplished with multiple outlet strips that plug into wall outlets. These work by dumping the excess current, sometimes into the ground conductor.
They wear out and need to be replaced occasionally. The best ones come with a test button to tell you whether they are still working.
There are also surge protectors that can handle the large loads caused by lighting strikes. These are slower to respond but have high capacity. Check with your local electric utility before installing this type of protector.
If lighting storms are common in your area, you may want to install a high-capacity surge protector in addition to the plug-in types that handle small surges. Surge protectors should be listed by Underwriters’ Laboratories (UL).
Using a voltage tester. This handy device lights up whenever household current passes through it. Use it to test whether wires or devices are hot and to see if outlets are properly grounded. To test for current, hold one of the prongs against a known ground and touch the other prong to all wires and connections.
If the tester lights up, the wire is hot. Try all possible connections with both prongs. To check for proper grounding, hold one prong in the short (hot) slot of the receptacle and touch the other prong to the grounding hole and then the faceplate screw. It should light up both times.