Terminology

WIRING SCHEMES AND GROUNDING Electrical Distribution Systems Terminology To understand wiring schemes used in power distribution systems, you must be familiar with the following terms. Ampacity - the current in amperes that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Bond - the permanent joining of metallic parts or circuits assuring electrical continuity and capacity to safely conduct any current likely to be imposed. Conductor - any wire, cable, or substance capable of carrying an electrical current. Ground - a conducting connection, whether intentional or accidental, between a circuit or piece of equipment and the earth, or some body serving as earth; a place of zero electrical potential. Ground voltage - the voltage between any given conductor and any point at ground potential. Leg - a current-carrying conductor intended to deliver power to or from a load normally at an electrical potential other than ground. Neutral - a current-carrying conductor normally tied to ground so that the electrical potential is zero. Phase voltage - the greatest root mean square (effective) difference of potential between any two legs of the circuit. Single-Phase Power The source of single-phase (1f) power in all facilities is by generation from a single-phase generator or by utilization of one phase of a three-phase (3f) power source. Basically, each phase of the 3f distribution system is a single-phase generator electrically spaced 120 degrees from the other two; therefore, a 3f power source is convenient and practical to use as a source of single-phase power. Single-phase loads can be connected to three-phase systems utilizing two methods. The diagram shown in Figure 15 illustrates these connections. ES-15 Page 22 Rev. 0