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Need & requirements for electrical grounding systems: this document discusses the details of why we need grounding, and definitions of electrical grounding and electrical bonding (what's the difference between these two terms.
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Bud - Master Electrician, State of Minnesota
Electrical “Grounding” has two jobs in a building: an “earthing” and a “bonding” function.
What is Electrical Grounding? "Earthing"
A major purpose of “grounding” is to provide a path so a “short” will trip a breaker. That requires a low resistance path back to the power source, which is the utility transformer. The path relies on a neutral-ground connection required at all [not entirely true] services.
The second "grounding" function is actually a collection of three safety functions:
The 2nd grounding function described above is accomplished by connecting the power neutral (the neutral wire entering from the utility company's service) at the service to an earthing electrode (ground rod). Provided it's a real earthing electrode not a fake one as we found in our photo (left).
The 3rd grounding function described above is accomplished by both of the above.
Practically, all three grounding functions are accomplished by a required neutral-ground connection at the power service, with the combined neutral-ground connected to an earthing electrode or electrodes. This function might best be called “earthing”.
What is Electrical Bonding?
The path is from a ground conductor [which is not necessarily a wire] to the service panel, through the neutral-ground connection, and back to the transformer via the service neutral. To provide high current to trip a breaker this must be a metal path.
The earth is far too high in electrical resistance and is not allowed to be the path. In fact this function will work if the service is not connected to earth. This function might best be called “bonding”.
Connecting exposed metal together to minimize voltage between surfaces is also a “bonding” function.
There might be some virtues to showing the Neutral-to-Ground bond (called the main bonding jumper). As I wrote previously, it is barely visible in the Carson Dunlap diagram (above) with “Electrical path for ground and neutral wires”.
When a professional examines the interior of a main electrical panel, she looks to see if there has a strap for the bond between neutral and ground buses and to the grounding conductor leading to the earthing rod (ground rod). In some panels such as SquareD the bond is a screw (and very hard to identify if you don’t know what to look for - some home inspectors have trouble finding Neutral-Ground bonds.)
See Definitions of Electrical Ground, Grounding Electrode, Grounding Conductor, Grounded Conductor, Ground Wire, Neutral Wire, Ground Rod, for definitions of these confusing electrical terms.
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