Rockwell Automation DeviceNet Media Design Installation Guide - Manual (Page 79)

1 Publication DNET-UM072C-EN-P - July 2004
Chapter
4
Determine Power Requirements
In this chapter, we describe two methods for determining your system’s power
requirements:
• the look-up method
• the full calculation method
Try the look-up method first, then move on to the full calculation method if
you cannot meet your configuration requirements.
Class 1 (CL1) cable Per NEC specifications for a Class 1 circuit (see NEC Article 725), the energy
at any point in the circuit is limited to 1000 VA. A Class 1 circuit requires that
the cables used must have jacketing with 600V isolation and pass the CL1 burn
test.
The DeviceNet specification indicates that the power source must be a
regulated maximum of 24V dc, and the power circuit be limited to 8A.
Applying this to a Class 1 circuit running at 24V dc, a DeviceNet-certified
cable with a 600V jacket isolation rating meets all requirements to be used in a
Class 1 circuit. So, based on the DeviceNet specification, the cable’s power-
carrying conductors are sized for an 8A maximum load.
IMPORTANT
You must consider two areas when powering output
devices using the DeviceNet power supply:
• (1) Wide DeviceNet voltage range of 11-25V dc
• (2) Noise or transient protection at each device
You must calculate a worst-case situation, and maintain
voltage within the 11-25V dc range on all segments. This
can be accomplished using diodes or other similar
techniques. See Appendix B, Powering Output Devices, for
more information.