Wiring Digest
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The Importance of Grounding and Bonding
Around the Circuit - Posted: 2011-01-22 21:16:07
Author: H. L. Williams

GroundingGrounding in electrical systems in homes and industries is what many persons take for granted. Persons would cut out the grounding pin from the plug of an appliance so that the plug could fit in a 2-pin socket. I once saw a man installing a fluorescent lamp and the first thing he did before connecting the switch was to cut out the ground-wire from the cable. I wondered then if the man was a certified electrician. Clearly, people do these things because they do not understand the importance of grounding in an electrical system.

The main reason for grounding in electrical systems is safety. Electrical equipment often carries metallic cabinet or case that can become energised due to insulation failure within the equipment. If that happens, then the equipment case will carry a dangerous voltage that can give a severe shock to anyone who touches it. To prevent this, the metal cases of all electrical equipment (and any metallic part that could be accidentally energized) are connected to a grounding electrode embedded in the earth, or to a building grounding system. Essentially, this is what is called grounding. A conductive (metal) surface is said to be grounded when it is effectively connected to earth.

When a conductive surface is properly grounded, if it becomes energised due to some insulation failure, then the electricity will be conducted to earth. This will create a short-circuit in the process, and immediately trips the supply circuit breaker. With the circuit-breaker tripped, there will be no dangerous voltage existing as a shock risk to anyone. For the circuit breaker to be reset and resume supplying electricity, the short-circuit problem would have to be cleared. It should be mentioned here, however, that the National Electrical Code (NEC) has some specific requirements for effective grounding. This is to ensure that the source circuit-break trips whenever a grounded surface is energised. Grounding should, therefore, be carried out by a certified electrician.

Usually, the items in our installations which are directly grounded through cables are the metallic cabinets of main circuit breakers or switches, sub-main breakers, lamps, transformers, and distribution panels. Electrical appliances that are plugged to power outlets receive their grounding via the outlets. A typical power outlet will have three ports: a “live” port, a neutral port, and a ground port (see photo right). The ground-port on the power outlet should be properly grounded (connected to the ground electrode or building grounding system).

An electrical appliance with metallic case or cabinet will have a cord with a 3-pin plug at the end. Similar to the outlet, the three pins are “live”, neutral, and ground (see photo right). Within the appliance cord there will be a grounding cable connecting the metallic case of the appliance and the ground-pin on the plug. When the appliance is plugged into the socket outlet, the three pins of its plug connect with the corresponding ports of the outlet. As a result, the metallic case of the appliance will have a connection to earth (grounded) through the ground-port of the power outlet. This provides protection against severe electric shock in the event the conductive case of the appliance becomes energised.

Similarly, bonding is employed to protect persons from accidental electric shock. It is used mostly where several electrical devices with conductive surfaces are installed close to each other. Of course, these conductive surfaces will have to be grounded. In addition, however, all the conductive surfaces of all the equipment are connected together usually by cables. This is called bonding.

When electrical equipment with conductive surfaces are in close proximity, certain phenomena can cause the surfaces to be at different potential. If someone should touch the surfaces of two different equipment at the same time, that person could receive a shock. To prevent this, bonding is used to keep the conductive surfaces of various equipment at the same potential. With no potential difference between surfaces, there will be no shock risk.

So, grounding and bonding should not be taken for granted; they play an important role in safeguarding us from electric shock. We should always ensure that our electrical equipment with conductive cabinets are properly grounded. Therefore, do not cut out the ground-pin from the plug of your appliance so that the plug can fit into a 2-pin outlet. Instead, replace the 2-pin outlet with a 3-pin one, and ensure that its grounding port is properly grounded. In that way, your appliance will be grounded when in use, providing some safeguard against electric shock.

It should be noted also that grounding is used for the protection of electrical equipment against lightning and other surges. The article entitled "Protect Your Appliances from Surge", which is posted on this site, states that for a surge suppressor to provide effective protection to your appliance against surges, the outlet to which the suppressor is plugged must be properly wired and grounded. This is another indication of the importance of grounding.

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