6
3.
There are two terminals for the dry alarm relay contacts, again with no polarity preference. The alarm relay can switch up to 0.5
A 120 V, or 60 VA. The alarm relay is activated if gas reaches or exceeds the alarm settings. See OPERATION section of the
detector User Instructions for details on relay settings.
4.
The alarm relay can be configured to normally open (default) (N.O.) or normally closed (N.C.) and will activate if the gas
concentration exceeds alarm set point. It will deactivate once the gas concentration drops below the alarm set point. Note that
the “disable” setting will cause the alarm relay not to engage at all.
5.
The dry contact, SPDT fan relay has three terminals. The common (COM.), normally open (N.O.) and the normally closed (N.C.)
contact. The fan relay can switch up to 5.0 A up to 240 VAC. See detector OPERATION section of the detector User
Instructions for details on relay settings.
Connection
The Macurco MRS-485 output is connected via a four terminal screw type connector. The MRS-485 adapter is wired in the standard
2W-Modbus circuits definition with selectable built-in terminating resistors at the ends of the RS-485 bus. The power for the MRS-
485 adapter is connected via a two terminal screw type connector, 12 to 24 VAC or 12 to 24 VDC and no polarity.
Note: Running the Modbus cable adjacent to or in the same conduit with high voltage wires is not recommended as there may be
interference from the high voltages. Line polarization should not be required for the MRS-485 but may be required for other devices
on the RS485 line - see manufacturer’s directions.
