8
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.
Grounding
The Common circuit (COM) must be connected directly to protective ground, preferably at one point only for the entire bus.
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.
Maximum Run Length
Wire gauge feet meters
18
500 152
16
800 244
14
1250 381
DIP Switches and Addressing
Each MRS-485 (and the partner gas detector) must be configured to a unique address. If there are 10 detectors on the serial line,
then 10 unique addresses must be used, one for each detector. To set the address use the eight DIP switch positions. For each unit
choose the value from 1 to 247 (see chart) and set the eight switches to match the address. UP means ON or 1 and DOWN means
OFF or 0. For example, to configure a unit as address “50”, set switches “2, 5, 6” (see table) to ON or in the up position (01001100).
See page 11 for a list of applicable addresses and dip-switch settings.
