We are seeing more and more of this type of set-up, where an auxiliary piece of equipment on an assembly/production line has two (2) electrical supplies. One is from the main SWITCH on the line, and one is from a separate source. This is usually done when the auxiliary equipment may need to stay energized during interruptions.
An excellent example is a hot glue machine used in packaging machines. Maintenance and Servicing may need to be performed on the packaging machine; however, this work is void of any exposure to hot glue. If the glue machine is shut down using the LOTO procedure for the packaging machine, the glue cools and becomes a significant hindrance to a speedy restart of the machine. Hence, a lot of manufacturers will run two (2) separate power sources to the glue machine. This is intended to make LOTO easier, as using the simple electrical disconnect makes the machine “servicing ready” (more on this below) for operators to interact with the machine.
But when a piece of equipment/machinery has “energy from more than one source,” the National Electric Code requires the following as it would apply to electrical labeling and our LOTO practices:
(emphasis by me)