Data Flow Systems TCU800, Installation And Operation Manual, Page: 44 / 162

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C h a p t e r 4
Externally-Supplied Bias Voltage Source
Externally supplied bias voltages can be used to bias the inputs. If the voltage is greater than 30 VAC/VDC, a voltage-
dropping resistor must be placed in line with the input. A minimum voltage of 10 VAC/VDC is required to indicate an ON
state for the digital monitor inputs.
Input commons on the TCU must be either AC neutral (with no voltage potential when referenced to earth
ground) or the negative terminal of a DC power supply.
Biasing an Input with an External Source
Motor Run Monitoring Signal
For each pump controlled by the TCU, a corresponding motor run input (MTRx_RUN) must be connected. The bias
voltage for the motor run input (MTRx_RUN) is taken from one phase of the motor power at the output of the motor
breaker and through the motor starter auxiliary contact. Connect a wire from this point, through a voltage-dropping resistor,
to the corresponding motor run input (P2-1 for MTR1_RUN, P2-2 for MTR2_RUN, and P2-3 for MTR3_RUN). Connect
the IN_COM_1 terminal (P2-5) to the neutral.
The transformer must provide AC neutral. When wiring to a typical three-phase, 4-wire, 240 V transformer
that provides AC neutral, refer to “Motor Run Monitoring Signal (4-wire transformer)”. Refer to “Motor Run
Monitoring Signal (3-wire transformer)” when connecting to a typical three-phase, 3-wire 480 V transformer
with no neutral provided. Input commons on the TCU must be either AC neutral (with no voltage potential when
referenced to earth ground) or the negative terminal of a DC power supply.
These diagrams are for typical installations. If your installation deviates from that shown here, then refer to the
National Electrical Code® (NEC®) Handbook.