Class 2 (Cl2) Cable - Parker H Series Installation & Service Instructions Manual

4-2 Determine Power Requirements

Class 2 (CL2) Cable

Publication DNET-UM072C-EN-P - July 2004
Per NEC specifications for a Class 2 circuit (see NEC Article 725), the energy
in the circuit anywhere is limited to 100 VA and the cable's jacketing must have
a 300V minimum isolation rating. Based on a 30V dc system, your circuit
would be limited to 3.3A.
The DeviceNet specification indicates the power source be a maximum of 24V
dc. Applying this to a Class 2 circuit running at 24V dc, the maximum
allowable current is 4A. A DeviceNet-certified cable with a 300V jacket
isolation rating meets all requirements for use in a Class 2 circuit. So, based on
the DeviceNet specification, the cable's power carrying conductors are sized
for a 8A maximum load.
The current Allen-Bradley Thick cable power conductors are sized to handle at
least 8 amps of power. However, NEC and CEC regulations force this cable to
be a CL2 (100 VA, 4 amp max) cable due to the construction of the cable.
Specifically, the insulation on the data pair is a foam PE, which will not pass at
CL1 burn test. As a result, any system using a Thick trunk and Thin drop must
be a CL2 installation in US and Canada.
KwikLink trunk cable is rated for CL1 applications and the conductors can
carry 8 amps of power.For more information, see Appendix A.
The DeviceNet specifications provide for both open- and closed-style wiring
terminations. You can design a wiring system for a DeviceNet installation that
lays out a trunk line in accordance with the requirements of the Class 1
guidelines and uses drop lines in accordance with Class 2 guidelines. Care must
be taken at the point where the two guidelines meet. At that point you must
limit the energy on each wire to be in accordance with the NEC guidelines.
Energy in the drop line must be limited to no more that 100 VA. How you
accomplish that is your decision. Most people resolve this issue by isolating the
trunk from the drop line with different power sources. Other ways to limit
energy may give you the same protection.