Engineering Specification and Drawings

DOE-HDBK-1092-98

4.1.1 ENGINEERING SPECIFICATIONS AND DRAWINGS

Engineering specifications and drawings should identify the requirements for all components and

clearly illustrate the grounding electrode system, the grounding electrode conductor, bonding points

and bonding jumpers, and the connection point for the grounded conductor and the grounding

conductors. Where used for installation or construction purposes, these specifications and drawings

should also include detailed installation instructions.

4.2 CIRCUIT AND SYSTEM GROUNDING

Circuit and system grounding consists of connecting the grounded conductor, the equipment

grounding conductor, the grounding busbars, and all noncurrent-carrying metal parts to ground. This

is accomplished by connecting a properly sized unspliced grounding electrode conductor between

the grounding busbar and the grounding electrode system. There are three fundamental purposes for

grounding an electrical system:

1. To limit excessive voltage from lightning, line surges, and crossovers with higher voltage lines.

2. To keep conductor enclosures and noncurrent-carrying metal enclosures and equipment at zero

potential to ground.

3. To facilitate the opening of overcurrent protection devices in case of insulation failures because

of faults, short circuits, etc. [See the fine-print note (FPN) to NEC Section 250-11.]

4.3 EQUIPMENT GROUNDING

Equipment grounding systems, which consist of interconnected networks of equipment grounding

conductors, are used to perform the following functions:

1. Limit the hazard to personnel (shock voltage) from the noncurrent-carrying metal parts of

equipment raceways and other conductor enclosures in case of ground faults, and

2. Safely conduct ground-fault current at sufficient magnitude for fast operation of the circuit

overcurrent protection devices.

To ensure the performance of the above functions, equipment grounding conductors are required to:

1. Be permanent and continuous per NEC Sections 250-51, 250-75, 250-76, 250-77, 250-91,

300-10 and 300-12;

2. Have ample capacity to safely conduct ground-fault current likely to be imposed on them per

NEC Table 250-94, Table 250-95, and Section 250-79(d) and (e); and

3. Have impedance sufficiently low to limit the voltage to ground to a safe magnitude and to

facilitate the operation of the circuit overcurrent protection devices per NEC Sections 300-3(b)

and 250-57(b).

See Appendix D, Reference Matrix.

4-2