GE Power Management
MM2 Motor Manager 2
C-1
APPENDIX C
C.1 DO’S AND DONT’S
C
APPENDIX C DO’S AND DONT’SC.1 DO’S AND DONT’S
C.1.1 CHECKLIST
For proper and reliable operation of the GE Power Management MM2 Motor Manager 2, it is impera-
tive that the steps, recommendations and practices listed below be adhered to at all times. This DO’s
and DON’Ts checklist has been compiled as a result of years of trouble free operation by a variety of
GE Power Management products.
a) MM2 GROUNDING
Users are requested to ground terminals 21, 48 (safety ground) and 22 (Filter ground) directly to the
GROUND BUS using a heavy gauge wire or braided cable. Terminals 21, 22, and 48 will accept up
to #12 AWG wire. These terminals must be grounded for proper filtering of noise, and protection
against transient conditions.
b) GROUNDING OF PHASE AND GROUND CTS
All external phase CT and ground CT secondary windings must be grounded to the GROUND BUS
to keep the potential difference to a minimum. If the CT secondary windings are not grounded,
capacitive coupling could allow the CT secondary voltage to float up to the voltage of the mains. This
is a serious safety hazard. Note: Terminal 20 of the External Ground CT is internally grounded there-
fore do not ground terminal 19 since the Ground CT signal would then be shunted.
It is also recommended that, in addition to the solid grounding of the ground CT described above, a
shielded twisted pair cable be employed when using the GE Power Management 50:0.025 ground
CT. The reasoning behind this recommendation is that the 50:0.025 ground CTs are typically used on
high resistance grounded systems where the fault currents are limited to less than 200 A. The alarm
and trip levels on these systems are usually between 0.5 A and 15.0 A. This equates to a secondary
current of 0.25 mA to 7.5 mA. Due to the very low levels that must be monitored by the MM2, any
noise picked up by these secondary wires must be kept to a minimum.
c) RS485 COMMUNICATIONS PORT
The MM2 interfaces with PCs, PLCs, and DCSs using the Modicon Modbus RTU protocol. The MM2
supports Modbus function codes 01, 03, 04, 05, 06, 07, 08, and 16. The communications port is a
very important part of the MM2’s process and control applications. The port allows reading and writ-
ing of data as well as full control to start and stop the motor from a remote location. For these rea-
sons, proper wiring practices are critical.
•
A shielded, twisted pair cable, such as 24 gauge Belden 9841 (120
Ω
characteristic impedance)
or equivalent, MUST be used for the communications link. The cable should be routed away from
all power carrying cables, such as the motor mains, power supply wiring, CT wiring and noisy
contactors or breakers.
•
When using the GE Power Management 232/485 converter box at the MASTER, GE Power
Management recommends placing no more than 32 GE Power Management devices on the
same data link which should be of no greater length than 4000 ft. The devices on the data link
should be daisy chained for reliable operation. Star or stub connections are not recommended.
If more than 32 devices are required to go onto the data link, or the distance must be greater than
4000 feet, consult the EIA 485 standard for more details on specific calculations. Another way to
increase the number of units on the data link or the transmission length is to utilize a RS485
Repeater.
Summary of Contents for MOTOR MANAGER 2
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Page 34: ...3 8 MM2 Motor Manager 2 GE Power Management 3 3 THEORY OF OPERATION 3 HARDWARE 3 ...
Page 80: ...5 12 MM2 Motor Manager 2 GE Power Management 5 5 A4 STATISTICS 5 ACTUAL VALUES 5 ...
Page 188: ...9 40 MM2 Motor Manager 2 GE Power Management 9 13 SOFT STARTER 9 STARTER TYPES 9 ...
Page 212: ...E 4 MM2 Motor Manager 2 GE Power Management E 1 CT ISOLATION APPENDIXE E ...
Page 220: ...iv MM2 Motor Manager 2 GE Power Management INDEX ...
