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)
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430.113 Energy From More Than One Source Motor and motor-operated equipment receiving electric energy from more than one source shall be provided with disconnecting means from each source of electric energy immediately adjacent to the equipment served. Each source shall be permitted to have a separate disconnecting means. Where multiple disconnecting means are provided, a permanent warning sign shall be provided on or adjacent to each disconnecting means indicating that multiple sources must be shut off to remove all power to the equipment. The sign at each disconnect shall identify the other specific circuits. Exception No. 1: Where a motor receives electric energy from more than one source, the disconnecting means for the main power supply to the motor shall not be required to be immediately adjacent to the motor if the motor controller disconnecting means is lockable in accordance with 110.25. Exception No. 2: A separate disconnecting means shall not be required for a Class 2 remote-control circuit complying with Parts I and II of Article 725, rated not more than 30 volts, and isolated and ungrounded. |
And let me caution you on using a basic sign to meet this CRITICAL SAFETY requirement! As you can see below, this sign is pretty common to find in these arrangements. But if we look above at the blue highlighted text we can see the critical info required to be on the sign is clearly missing!
