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Grounding electrode system
Note that full coverage of how to install a grounding electrode system is well beyond the scope of this FAQ. The comments made here are primarily so that the reader understands what it is for, and some of its characteristics. The grounding electrode system is a method by which the neutral and grounding conductors are connected to the common "earth" reference. The connection from the electrical system to the grounding system is made in only one place to avoid ground loops. The grounding electrode system is _not_ intended to carry much current. Ground faults (Ie: hot to grounded case short) are conducted down the ground wire to where it is interconnected with the neutral and hopefully the breaker/fuse trips. The grounding electrode does not participate in such a situation. While the conductors involved in this are relatively large, they're sized for lightning strikes and other extremely short duration events. The grounding electrode system is specifically _not_ expected to have enough conductivity to trip a 15A breaker. The grounding electrode often has a moderately high resistance. For example, according to the NEC, an acceptable ground electrode system may have 25 ohms of resistance - only 5A at 120V, not enough to trip a 15A breaker. A grounding electrode system usually consists of a primary grounding electrode, plus possibly a secondary electrode. A primary electrode can be (if in direct contact with the earth): 10' of ground rod. 10' of well casing or metallic water pipe (must be connected within 5' of pipe entrance to house). 20' of copper wire buried in the bottom of the footings. A secondary electrode will be required if the primary is a water pipe or (NEC) if the primary electrode is >25 ohms to the dirt.
Top Document: Electrical Wiring FAQ (Part 1 of 2)
Previous Document: What's the purpose of the ground prong on an outlet, then?
Next Document: Bonding requirements
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clewis@ferret.ocunix.on.ca (Chris Lewis)
Last Update October 11 2008 @ 00:12 AM