210.5(C)(1), Exception.  In existing installations where a voltage system(s) already exists and a different voltage system is being added, it shall be permissible to mark only the new system voltage.  Existing unidentified systems shall not be required to be identified at each termination, connection, and splice point in compliance with 210.5(C)(1)(a) and (b).  Labeling shall be required at each voltage system distribution equipment to identify that only one voltage system has been marked for a new system(s).  The new system label(s) shall include the words “other unidentified systems exist on the premises.”

Comment:  The general requirement for premises wiring systems is that where more than one nominal voltage system exists, each ungrounded branch circuit conductor shall be identified by phase or line and system at all terminations, connections, and splice points and the method utilized for identification posted at each branch-circuit panelboard or similar branch-circuit distribution equipment.  The new exception provides relief from identifying each ungrounded conductor of existing voltage systems where a different voltage system is being added.  However, labeling is required at each voltage system distribution equipment to identify that only the new voltage system has been marked.  The new system label(s) shall include the words “other unidentified systems exist on the premises.”  The label shall be of sufficient durability to withstand the environment involved and shall not be handwritten.