Sizing and Purposes for Good Grounding Practices:

Reasons:

	The main purpose of the grounding system is to disconnect the
electrical supply to a shorted or damaged circuit, so that no one will
be injured by that circuit.

        To prevent damage to life and property one should keep up good
grounding practices. Section 250 of the National Electrical Code of the 
United States describes in detail the rules to follow for proper grounding.
These rules should be followed regardless of whether or not there is a
ruling authority for the enforcement of them.

        It is beyond the scope of this article to give a complete 
	description with all the rules; only to provide an overview:

	The electrical system should be grounded at the point of entry to
the building. The grounding electrode should be attached to the neutral 
conductor at that point. The neutral and the ground system should join at
the main panel serving the area. This provides a Commonground, one
that is of the opposite potential of the power supply, insuring that a
breaker will trip should there be a short circuit.
	
	The ground electrode and the neutral conductor should be connected
or bonded to the electrical panel at this point, all metal parts should also
provide a continuous path to the panel. In other words the conduit and other
metal parts should be connected in a continuous circuit to this panel, providing
an additional ground protection for the system.

Sizing:


	All ground conductors must be of sufficient size to trip the
circuit breaker or fuse of the circuit that it protects, without
overheating 15 amp circuit 15 amp wire, 20 amp circuit 20 amp wire. 
Refer to tables 250-94 and table 250-95, 1987 NEC (National Electrical Code).


	The size of the ground conductor to the ground electrode is
dependant on the size of the largest current carrying conductor,
refer to section 250 of the code book for exact sizes, but under normal
circumstances you should use a # 6 copper thru size 0, # 4 thru size 3/0,
# 2 thru 350 mcm.

	A 200 amp equipment ground should be a # 6 copper or # 4 aluminum.

	A 200 amp service requires a # 4 copper ground conductor to a 1/2 inch
copper 8 foot ground rod. The code gives other options.
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