WIRING SCHEMES AND GROUNDING
Electrical Distribution Systems
Wiring Schemes And Grounding Summary
Terminology
Ampacity - current-carrying capacity of a conductor in amperes
Bond - permanent joining of metallic parts or circuits assuring electrical
continuity
Conductor - any wire, cable, or substance capable of carrying an electrical
current
Ground - a conducting connection between a circuit or piece of equipment and
the earth, or some body serving as earth
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
Neutral - a current-carrying conductor intended to deliver power to or from a
load normally at an electrical potential other than ground
Phase voltage - the greatest root mean square (effective) difference of potential
between any two legs of the circuit
Two methods to connect single-phase loads to a three-phase system are:
Phase-to-phase
Phase-to-ground
The purposes of the following wiring schemes are:
3-wire, single-phase Edison system - the only approved method of wiring single-
phase power
3-wire, three-phase Delta system - normally used for transmission of power in
the intermediate voltage class from approximately 15,000 volts to 600 volts
4-wire, three-phase Delta system - combines the ungrounded Delta for three-
phase loads with the convenience of the Edison system for single-phase loads
4-wire, three-phase Wye system - the safest possible multi-purpose distribution
system for low voltage
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