Mike Dolt Enterprises
Mike Dolt Enterprises
User: sirdle, Location: California
Asked on: Wednesday, April 6, 2011 at 10:31 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:53 am EDT
Question: I don't work much with communications equipment and I'm not sure which code articles apply or even where to start looking.I often see PLC cabinets installed in Tank Farms. In addition to 120V ac and 24V dc equipment, these cabinets might include:A) PLC-based RS-485 communications module connected to a remote Modbus instrument.B) PLC-based TCP/IP module connected to a din rail-mounted Ethernet switch.C) Power-over-Ethernet switch connected to a remote spread-spectrum radio.D) Protocol converter to switch between Ethernet and RS485.1) Are any of these devices considered "Communications" equipment?2) Would the cables connecting them be covered under Article 800, 810 or 830?3) Or would these be considered to be extensions of the Class 1, 2, and 3 circuits covered under Article 725?Thanks
1) Communications Equipment
A) PLC-based RS-485 communications module connected to a remote Modbus instrument:
Yes B) PLC-based TCP/IP module connected to a din rail-mounted Ethernet switch: Yes C) Power-over-Ethernet switch connected to a remote spread-spectrum radio: Yes D) Protocol converter to switch between Ethernet and RS485: Yes
All of these devices are used for communication purposes and fall under the definition of "communications equipment" in Article 800.2) Cable Types
Cables connecting the RS-485 module (A) to the Modbus instrument are considered
Communications Cable and are covered by Article 800. Cables connecting the Ethernet switch (B) to the spread-spectrum radio (C) and the Ethernet switch (B) to the protocol converter (D) are also considered Communications Cables and are covered by Article 800.3) Class 1, 2, or 3 Circuits
While the devices may be connected to Class 1, 2, or 3 circuits (such as the PLC or power supply), the cables connecting the communications equipment are not considered extensions of those circuits. They are considered separate communications cables and are covered by Article 800.
Additional Considerations: These communications cables should be installed in accordance with the requirements of Article 800, including proper routing, protection, and bonding. The equipment should be properly grounded and protected from electrical hazards. It is recommended to consult with a qualified electrician or communications professional to ensure proper installation and compliance with all applicable codes and standards. Flag for review