GROUNDING
Grounding is one of the most important aspects of an electrical distribution system but often the least understood. Your Electrical Code sets out the legal requirements in your jurisdiction for safety standards in electrical installations. For instance, the Code may specify requirements in the following areas:(a) The protection of life from the danger of electric shock, and property from damage by bonding to ground non-current carrying metal systems;
(b) The limiting of voltage on a circuit when exposed to higher voltages than that for which it is designed;
(c) The limiting of ac circuit voltage-to-ground to a fixed level on interior wiring systems;
(d) Instructions for facilitating the operation of electrical apparatus
(e) Limits to the voltage on a circuit that is exposed to lightning.
In order to serve Code requirements, effective grounding that systematically connects the electrical system and its loads to earth is required.
Connecting to earth provides protection to the electrical system and equipment from superimposed voltages from lightning and contact with higher voltage systems. Limiting over voltage with respect to the earth during system faults and upsets provides for a more predictable and safer electrical system. The earth ground also helps prevent the build-up of potentially dangerous static charge in a facility.
The grounding electrode is most commonly a continuous electrically conductive underground water pipe running from the premises. Where this is not available the Electrical Codes describe other acceptable grounding electrodes.
Grounding resistances as low as reasonably achievable will reduce voltage rise during system upsets and therefore provide improved protection to personnel that may be in the vicinity.
Connection of the electrical distribution system to the grounding electrode occurs at the service entrance. The neutral of the distribution system is connected to ground at the service entrance. The neutral and ground are also connected together at the secondary of transformers in the distribution system. Connection of the neutral and ground wires at any other points in the system, either intentionally or unintentionally, is both unsafe (i.e., it is an Electrical Code violation) and a power quality problem.
EQUIPMENT BONDING
Equipment bonding effectively interconnects all non-current carrying conductive surfaces such as equipment enclosures, raceways and conduits to the system ground. The purpose of equipment bonding is:1) To minimize voltages on electrical equipment, thus providing protection from shock and electrocution to personnel that may contact the equipment.
2) To provide a low impedance path of ample current-carrying capability to ensure the rapid operation of over-current devices under fault conditions.
