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CHAPTER 2: INSTALLATION
2.3.1
Phase CT
Inputs
2.3.2
Ground Fault
CT Input
NOTE
2.3.3
Supply Voltage
2.3.4
Ground Surge
2.3.5
External
Connections
2.3.6
Thermistor
Input
MM3 MOTOR MANAGER 3 – INSTRUCTION MANUAL
2.3
Inputs and Outputs
For motor full-load currents up to 250 A, the phase conductors can be directly connected
to the MM3 Motor Manager 3 without phase CTs. If external CTs are required, the
secondary winding should be looped though the MM3 Motor Manager 3 doughnut
opening.
Selected CTs should be capable of supplying the required current to the total secondary
load which consists of the connection wiring burden. The CT must not saturate under
maximum current conditions which can be up to 8 times motor full load during starting.
The ground fault detection consists of a 50:0.025 input (terminal 19) and a common input
(terminal 20), or residual connection of phase CTs (only the common input should be
externally grounded). Residual ground fault protection provides a sensitivity of 10% of
motor full load current. The 50:0.025 core balance (zero-sequence) CT input can be used
for improved sensitivity when measuring the ground fault current.
Care must be taken when enabling the ground fault trip feature. If the interrupting device
(contactor or circuit breaker) is not rated to break ground fault current (low resistance or
solidly grounded systems), the feature should be disabled. The 50:0.025 input is only
recommended to be used on resistance grounded systems.
A supply voltage of 120/240 V AC at 50/60 Hz is required to power the MM3 Motor
Manager 3. The label on the back of the unit specifies the voltage that has been internally
set. To change the voltage setting, open the sliding door on the back of the MM3 Motor
Manager 3 and locate the supply voltage selector slide switch. The selector slide switch
has a label affixed to show the 120/240 V AC positions. Set the slide switch to the desired
voltage.
This is an additional ground terminal provided for dissipating transient signals and surges.
This must be connected by a thick wire or braid to the system ground for reliable
operation.
Signal wiring is to box terminals that can accommodate wire as large as 12 gauge. Consult
Figure 2-2: Typical Wiring Diagram on page 2–2. Other features can be wired as required.
Either a positive temperature coefficient (PTC) or negative temperature coefficient (NTC)
thermistor may be directly connected to the MM3 Motor Manager 3. By specifying the hot
and cold thermistor resistance, the MM3 Motor Manager 3 automatically determines the
thermistor type as NTC or PTC. Use thermistors with hot and cold resistance values in the
range 100 to 30000 Ω. If no thermistor is connected, the
THERMISTOR
THERMISTOR TRIP
THERMISTOR ALARM
setpoints must be set to "Disable".
S1 CONFIGURATION
and
S1 CONFIGURATION
INPUTS AND OUTPUTS
THERMISTOR
2–3
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