B.1.1 Questions And Answers - GE MM3 Instruction Manual

APPENDIX B
APPENDIX B FREQUENTLY ASKED QUESTIONSB.1 MM3 FAQ
Listed below are some of the more frequently asked questions by users of the MM3. The list includes ques-
tions asked by consultants before the MM3 has even been specified to the end user and after the MM3 is
installed and controlling a motor.
Q
Does the MM3 support ladder logic as in a PLC?
No. The MM3 switch inputs do not allow total programmability as in PLCs; however, it does have a
A
range of over 30 different dedicated functions that can be assigned for typical applications. These
functions come complete with built in timers if necessary for that particular function. For example:
Auto Permissive and Auto Start for PLC hard wired control, Two Wire Control for PLC starts or jog-
ging, Process Interlocks with starting and running override timers for pressure and flow monitoring.
All the programmable switch inputs may be configured as normally open or normally closed.
Q
Does the MM3 have any hot winding protection?
Yes. The MM3 has a single thermistor input to protect the motor against hot windings. These ther-
A
mistors are typically wound into stator windings of the motor when manufactured and can be Positive
Temperature Coefficient (PTC) of Negative Temperature Coefficient (NTC).
After wiring the MM3 into the control circuit, it remains UNAVAILABLE for starts. What does
Q
this mean?
Three conditions can cause the MM3 to remain UNAVAILABLE for starts"
A
1. The MM3 has tripped on a trip condition
2. The STOP switch input (terminal 11) is not energized.
3. If a Process Interlock function is assigned to one of the programmable switch inputs and the star-
tup override is set to 0 seconds, the MM3 will remain UNAVAILABLE until that switch input is ener-
gized.
When a start is attempted, the motor starts for a second then shuts off. The MM3 displays an
Q
OPEN CONTROL CIRCUIT alarm. What is the problem?
The MM3 must see feedback from the Contactor A and, if used, Contactor B within 1 second of the
A
MM3 closing the contactor or the MM3 will stop the motor as it assumes that there is a problem in the
circuitry for the motor contactor coil. The feedback from the contactors go to the status inputs (termi-
nals 15 & 16) of the MM3. NOTE: This condition will result in the toggling of the motor contactor when
the MM3 is in the Two Wire mode as there can be a constant start signal from the two wire device.
Use the Open Control Circuit trip feature to prevent the toggling of the motor contactor.
After connecting the MM3 through an interface device to a PLC network, communications to
Q
the MM3 cannot be established. What is the problem?
GE Power Management MM3 Motor Manager 3
B.1 MM3 FAQ

B.1.1 QUESTIONS AND ANSWERS

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