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b. Factors which can degrade initial good grounds. Tests should always be made at times when the surrounding soil can be expected to have the least moisture. The following factors indicate the importance of continuous periodic testing of grounding systems.

(1) Water tables are gradually falling in many areas.

(2) There are more underground installations of nonmetallic pipes and conduits, which do not provide low-resistance ground connections.

(3) Electric systems are continually expanding with an associated fault current increase which may require a decrease in grounding resistance.

(4) Corroded connections may increase the re­sistance.

10-2. Grounding provisions.

Maintenance personnel deal with two types of grounding systems: permanent and temporary.

a. Permanent grounding systems. Permanent grounding is provided for the efficient, effective, safe operation of electrical power systems.

(1) Safety. Equipment grounding, which is the grounding of all exposed or accessible noncurrent-carrying parts of electrical devices and equipment, reduces the hazards of contact by personnel.

(2) System operation. System grounding, which is the grounding of one conductor point on an elec­trical circuit, stabilizes the voltages to protect the equipment and provides a basis for adequate protec­tive relaying.

b. Temporary grounding.

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