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1.1.2: Delta Connection
Delta connected services may be fed with either three wires or four wires. In a three-phase Delta service the load
windings are connected from phase-to-phase rather than from phase-to-ground. Figure 1.3 shows the physical load
connections for a Delta service.
Phase C
Phase A
Phase B
Figure 1.3: Three-Phase Delta Winding Relationship
In this example of a Delta service, three wires will transmit the power to the load. In a true Delta service, the phase-
to-ground voltage will usually not be balanced because the ground is not at the center of the delta.
Fig. 1.4 shows the phasor relationships between voltage and current on a three-phase Delta circuit.
In many Delta services, one corner of the delta is grounded. This means the phase to ground voltage will be zero for
one phase and will be full phase-to-phase voltage for the other two phases. This is done for protective purposes.
Vca
Ic
Vbc
Ia
Ib
Vab
Figure 1.4: Phasor diagram showing three-phase voltages, currents delta connected.
Another common Delta connection is the four-wire, grounded delta used for lighting loads. In this connection the
center point of one winding is grounded. On a 120/240 volt, four-wire, grounded Delta service, the phase-to-ground
voltage would be 120 volts on two phases and 208 volts on the third phase. Figure 1.5 shows the phasor diagram for
the voltages in a three-phase, four-wire Delta system.
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Electro Industries/Gauge Tech
Doc# E149701
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