10
MM300 MOTOR MANAGEMENT SYSTEM – QUICKSTART GUIDE
ELECTRICAL INSTALLATION
CHAPTER 2: INSTALLATION
CAUTION:
To ensure that all devices in a daisy-chain are at the same potential, it is imperative
that the common terminals of each RS485 port are tied together and grounded only
once, at the master or at the MM300. Failure to do so may result in intermittent or
failed communications.
The source computer/PLC/SCADA system should have similar transient protection devices
installed, either internally or externally. Ground the shield at one point only, as shown in
the figure above, to avoid ground loops.
Correct polarity is also essential. The MM300 IEDs must be wired with all the positive (+)
terminals connected together and all the negative (–) terminals connected together. Each
relay must be daisy-chained to the next one. Avoid star or stub connected configurations.
The last device at each end of the daisy-chain should be terminated with a 120 ohm ¼
watt resistor in series with a 1 nF capacitor across the positive and negative terminals.
Observing these guidelines will ensure a reliable communication system immune to
system transients.
Phase current inputs (IO_A module)
Figure 2-13: Typical phase current input connections
Power flow
D1
D2
D4
D3
Phase current inputs
D5
D6
D7
CT1
CT2
CT3
D8
G/F
D1
D2
D4
D3
Phase current inputs
D5
D6
D7
CT1
CT2
CT3
D8
G/F
D1
D2
D4
D3
Phase current inputs
D5
D6
D7
CT1
CT2
CT3
D8
G/F
Two CT Connection
Direct Connection
Residual Ground Connection
Power flow
Power flow
Power flow
Power flow
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