Sys Req Pg 2

Factors Influencing Requirements
For A Good Grounding System:

In an industrial plant or other facility that requires a grounding system, one or more of the following must be carefully considered:

1. Limiting to definite values the voltage to earth of the entire electrical system.Use of to Superior Grounding System can do this by maintaining some point in the circuit at earth potential. The grounding system provides these advantages:

a. Limits voltage to which the system-to ground insulation is subjected,      thereby more definitely fixing the insulation rating.

b. Limits the system-to-ground or system-to frame voltage to values      safe for personnel.

c. Provides a relatively stable system with a minimum of transient
    overvoltages.

d. Permits any system fault to ground to be quickly isolated.

2. Proper grounding of metallic enclosures and supporting structures that are part of the electrical system and may be contacted by personnel. Also, to be included are portable electrically-operated devices. Consider that only a small amount of electric current-as little as 0.1 ampere for one second-can develop surprisingly high charges unless properly grounded.

3. Protection against static electricity from friction. Along with this are the attendant hazards of shock, fire and explosion. Moving objects that may be inherent insulators-such as paper, textiles, conveyor belts or power belts and rubberized fabrics-can develop surprisingly high charges unless properly grounded.

4. Protection against direct lightning strikes. Elevated structures, such as stacks, high rise buildings, water tanks, etc.- may require lightning rods connected into the grounding system

5. Protection against induced lightning voltages. This is particularly a factor if aerial power distribution and communications circuits are involved. Lightning arresters may be required in strategic locations throughout the plant.

6. Providing good grounds for electric process control and communication circuits. With the increased use of industrial control instruments, computers, and communications equipment, accessibility of low-resistance ground connections in may plant locations-in office and production areas-must be considered.