Installing control circuits per the National Electrical Code

Over the last two code cycles, changes have been made to requirements for the installation of control circuits. These changes have made the task of installing control circuits from PLC and DCS systems even more difficult than they were in the past. This paper outlines the changes and their impact. The paper makes suggestions on how to install control circuits to be in compliance with the current requirements. The paper also makes recommendations on changes to the National Electrical Code/sup /spl reg// (NEC/sup /spl reg//) [NFPA, 2002] that would make the requirements more easily understood and make the installations more economical without impacting the safety of the installation.