Difference between Bonding, Grounding and Earthing

Introduction:

• One of the most misunderstood and confused concept is difference between Bonding, Grounding and Earthing. Bonding is more clear word compare to Grounding and Earthing but there is a micro difference between Grounding and Earhing.
• Earthing and Grounding are actually different terms for expressing the same concept. Ground or earth in a mains electrical wiring system is a conductor that provides a low impedance path to the earth to prevent hazardous voltages from appearing on equipment. Earthing is more commonly used in Britain, European and most of the commonwealth countries standards (IEC, IS), while Grounding is the word used in North American standards (NEC, IEEE, ANSI, UL).
• We understand that Earthing and Grounding are necessary and have an idea how to do it but we don’t have crystal clear concept for that. We need to understand that there are really two separate things we are doing for same purpose that we call Grounding or Earthing.
• The Earthing is to reference our electrical source to earth (usually via connection to some kind of rod driven into the earth or some other metal that has direct contact with the earth).
• The grounded circuits of machines need to have an effective return path from the machines to the power source in order to function properly (Here by Neutral Circuit).
• In addition, non-current-carrying metallic components in a System, such as equipment cabinets, enclosures, and structural steel, need to be electrically interconnected and earthed properly so voltage potential cannot exist between them. However, troubles can arise when terms like “bonding,” “grounding,” and “earthing” are interchanged or confused in certain situations.
• In TN Type Power Distribution System, in US NEC (and possibly other) usage: Equipment is earthed to pass fault Current and to trip the protective device without electrifying the device enclosure. Neutral is the current return path for phase. These Earthing conductor and Neutral conductor are connected together and earthed at the distribution panel and also at the street, but the intent is that no current flow on earthed ground, except during momentary fault conditions. Here we may say that Earthing and grounding are nearly same by practice.
• But In the TT Type Power Distribution System (In India) Neutral is only earthed (here it is actually called Grounding) at distribution source (at distribution transformer) and Four wires (Neutral and Three Phase) are distributed to consumer. While at consumer side all electrical equipment body are connected and earthed at consumer premises (here it is called Earthing). Consumer has no any permission to mix Neutral with earth at his premises here earthing and grounding is the different by practice.
• But in both above case Earthing and Grounding are used for the same Purpose. Let’s try to understand this terminology one by one.

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Why was 120V chosen as the standard voltage of homes in the US and not some other voltage?

Answer:

The reason that 120v service was chosen, was economic. Originally electricity was delivered to homes, and most businesses, for a single purpose and that was lighting. Can openers, TVs, washers, dryers, electrical factory machinery, etc. came later. At the time the most cost effective form of light bulb was a carbon filament bulb that operated best (optimally) at 100v to 110v. This, adjusted for transmission voltage drop, set most supply lines at 120v.

Supplemental and Related Information:

By the time cost effective, and higher voltage, metal filament bulbs were brought to the market, most of the cities in the USA were already running 120v supply lines. Europe was just starting such systems and opted for higher voltage supply lines.

Higher voltages are used for long-distance transmission and power distribution because more power can be transferred over the same size wire at a higher voltage (lower current). Power generation plants often use voltages in the hundreds of thousands, 115,000 to 165,000 of volts to move power over long distances. For lines of up to 20 miles long around a city, 2400 volts works well to reduce the voltage loss in the wires.

In the United States, the electrical power lines going to residential streets and roads are operated from 2300 to 2400 volts. With a 2400 volt supply, it is very convenient and easy to design and build pole transformers that have a 10-to-1 step-down ratio, thus providing 240 volts to the houses. The transformers also have a center tap to provide 120 volts from each 240-volt leg to the center point. This center point tap also provides a convenient point for a grounding connection. The actual measured voltage in your house receptacle circuits will normally be 120 to 125 volts. All appliances are rated for the minimum operating voltage (110-115), thus there is much confusion about the actual level of the supply voltages.

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