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Macurco MRS-485 Modbus RS-485 Adapter
3.4.3
Length
The end to end length of the trunk cable must be limited. The maximum length depends on the baud rate, the
cable (Gauge, Capacitance or Characteristic Impedance), the number of loads on the daisy chain, and the
network configuration (2-wire). For a maximum 9600 Baud Rate and AWG26 (or wider) gauge, the maximum
length is 1000m 3281ft. The derivations must be short, never more than 20m 65.5ft. If a multi-port tap is used
with n derivations, each one must respect a maximum length of 40m 131ft divided by n.
3.4.4
Grounding
The Common circuit (COM) must be connected directly to protective ground, preferably at one point only for
the entire bus.
3.4.5
Power Wire
All field wiring is completed via modular connectors (provided). After wiring, simply plug the modular
connectors into the matching connectors on the MRS-485. The power connections to the remote mounted
detectors should be size AWG18 (minimum) for short runs. Since Macurco detectors are rated for operation
between 12 and 24 VDC or VAC, the voltage drop between the power supply and the MRS-485 should not be an
issue if the recommended power wire gauge guidelines below are followed. The terminals will accept wire from
16 to 28 AWG. To install a wire, strip back approximately 0.25 in. (6 mm) of insulation and insert the bare wire
into the terminal. Tighten the screw clamp and ensure that the wire cannot be easily pulled from the connector.
Wire gauge
18
16
14
REV – 1.0
Feet
500
800
1250
[34-2900-0019-8]
Meters
152
244
381
11 |
P a g e
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