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9.2 - Cable types and distances
The maximum total distance for a Modbus loop is 4,000 cable feet (1,219.2 m); however, this may not always be practical. The cable
impedance, load impedance, foreign signal presence, serial baud rate, and number of attached devices will decrease this maximum
distance limit. Testing has shown that the system has a solid signal strength on a 1,000-ft (304.8 m) loop; however, there is no way to
determine the maximum length for a particular application due to the number of variables.
There are a number of acceptable cable types that can be used for installation. On the following pages, Belden cable part number
3106A is used for all examples.
It is absolutely critical that the cable used meets TIA/EIA-485 standards for use on RS-485
networks.
Manufacturers that make acceptable cable include Carol
®
, Alpha Wire, Tyco/Raychem
®
, and Belden.
9.3 - Terminating or EOL resistors
A number of 1/4W, 120-ohm resistors are included in the provided hardware. As illustrated on the following pages, an EOL resistor
must be placed across the MBA and MBB terminals at the last device in a Modbus cable run, even if it is only a single run between the
gateway and a single fan.
9 - Big
Ass
Fans Electrical Installation (cont.)
