4
Cable Size: Cable size along with capacitance and DC resistance determine whether the cable is suitable for
the application. A 22-gauge cable will provide a proper balance of capacitance and resistance.
DC Resistance: DC resistance determines the maximum length of wire allowed for an application. The
maximum length is determined by the resistance of each twisted pair along with the device termination
resistance. The use of surge protectors with series resistance also contributes to loop resistance.
RTU
MJ-X
MJ-X
MJ-X
Twisted-pair
Cabling
4000 ft max. total
Figure 2-4 RS-485 Configuration – Loop Network
RTU
MJ-X
MJ-X
MJ-X
Twisted-pair
Cabling
4000 ft max. total
Figure 2-5 RS-485 Configuration – Star Network
RTU
MJ-X
MJ-XMJ-X
Twisted-pair
Cabling
4000 ft max. total
Figure 2-6 RS-485 Configuration – Open-Ended Network
3 Communication Protocols
The MJ-X
L
Control Panel is designed to be used in a network of intelligent power control devices communicating
with a supervisory device or remote terminal unit (RTU). Each device on the network has a specific
communications address assigned to allow messages to be directed to and from the device. Messages are
transmitted from the RTU to all devices and only the device with the specified address will respond. The MJ-X
L
Communications Module supports the following protocols. Refer to the documents listed for details about the
protocols.
• Distributed Network Protocol (DNP 3.0). (See User’s Group website: www.dnp.org)
• The Cooper 2200 Protocol (with or without address byte)
• MJ-3A Format “A”, “B1”, and “B2”
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