GE Masoneilan 469 Series, Instruction Manual

Page: 78 / 348

3–14 469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 3: INSTALLATION
FIGURE 3–14: Residual Ground CT Connection
The 469 measures up to 5 A secondary current if the 1 A / 5 A tap is used. Since the
conversion range is relatively small, the 1 A or 5 A option is field programmable. Proper
selection of this settings ensures proper reading of primary ground current. The 1 A / 5 A
ground CT chosen must be capable of driving the 469 ground CT burden (see
Specifications
on page 2–6). The 469 measures up to 25 A of primary ground current if this tap is used in
conjunction with the GE Grid Solutions core balance CT.
NOTE
Note
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.
NOTE
Note
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.