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
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