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Joined: Aug 2004
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I'm building a heater temperature control system in one enclosure for a customer. The customer requested that they will supply the enclosure with a 120VAC single phase 10A control power and 480VAC 3-phase 30A power for the heater. Does the NEC require any warning signs be posted on the outside of the enclosure to notify the user that the system is supplied by two power sources?
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Joined: Apr 2002
Posts: 2,527
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That is one reason why MCC cubicles {buckets} and combination starters are available with 480:120V control-power transformers — to limit hazardous/foreign voltages [below the disconnect line terminals] when the disconnect is opened.
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Joined: Oct 2000
Posts: 2,749
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Research Article 424, and see this because the logic is considered: 430.113 Energy from More Than One Source.
Motor and motor-operated equipment receiving electrical energy from more than one source shall be provided with disconnecting means from each source of electrical 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.
Exception No. 1: Where a motor receives electrical 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, provided the controller disconnecting means is capable of being locked in the open position.
Exception No. 2: A separate disconnecting means shall not be required for a Class 2 remote-control circuit conforming with Article 725, rated not more than 30 volts, and that is isolated and ungrounded.
Joe Tedesco, NEC Consultant
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Joined: Jul 2003
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In my industrial facility, we were required by OSHA to post signs on our panels indicating Dual Voltages and Multiple Voltages where that applied.
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Joined: March 2005
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