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Electrical hazard is the major problems in electrical

Why we need electrical grounding


The grounding system at a building provides an easy path for electricity to flow to earth should a problem, such as a short circuit, occur. Allowing current to flow to earth through the ground system helps assure that a circuit breaker will trip or fuse will blow should a problem occur. Properly operating these overcurrent devices help prevent fire and shock.

Should an electrical fault occur where no ground path is present, the electrical potential is just sitting there waiting for a person to come along, touch some component of the system, and by accidentally providing a path to earth through their body, receive a burn or potentially fatal shock.

 "Grounding" has 2 main functions.

 One is to provide a path to trip a breaker in the event of a 'short' as in the text above. That function relies on a "ground"-to-neutral connection required at services in the US (the "main bonding jumper"). The path is (branch circuit ground wire) to (N-G bond at the service) to (service neutral) to (utility power transformer). This path *must* be metallic back to the power transformer to provide low resistance to trip a circuit breaker. This function will work even if the service is not connected to earth. And the NEC *does not allow* earth to be used as part of this path.

One reason is the resistance of an earth path is too high. Assume the earthing is only through a ground rod and the rod has a quite good 10 ohms resistance to earth. Further assume there is a 'short' connecting hot to "ground". The current to earth will be 12A. There is a good chance this won't even trip a 15A circuit breaker. If the circuit is loaded the breaker will trip, but after a significant time delay. In the mean time, the "ground" potential with respect to the earth away from the ground rod will be 120V.

 1. Electrical grounding improves building electrical safety because it provides better path for current than a person, blows fuse/breaker, dissipates static, may dissipate lightning

2. Example of a potential shock waiting for someone: loose black wire in a metal junction box touches the side of the box. If the electrical box is connected to ground lots of current will flow (this is a short circuit) and the fuse or circuit breaker protecting the electrical circuit will blow or trip.

But if the electrical box is not grounded, current flows through a person when the electrical box or anything connected to it (electrically) is touched, if the person has the bad luck to also be herself grounded (say by touching building piping or standing on a wet floor).

Note that if you are using the earth as in the quote above, the path is not just into the earth. It is back to the power source, and also depends on the earth connection at the power transformer.

This would be better termed a *bonding* function.