GE 469 Instruction Manual page 58

469
Motor Management Relay
NOTE
NOTE
3–12
The zero-sequence connection is recommended. Unequal saturation of CTs,
size and location of motor, resistance of power system and motor core
saturation density, etc., may cause false readings in the residually
connected GF circuit.
Only one ground input should be wired – the other input should be
unconnected.
The exact placement of a zero-sequence CT to detect only ground fault current is
shown below. If the core balance CT is placed over shielded cable, capacitive
coupling of phase current into the cable shield during motor starts may be detected
as ground current unless the shield wire is also passed through the CT window.
Twisted pair cabling on the zero-sequence CT is recommended.
FIGURE 3–15: Core Balance Ground CT Installation – Unshielded Cable
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