Two separate voltages, one cabinet

[Geneva Rich]

Can you have a control cabinet with a 480 source to a disconnect AND a 120 source to the cabinet that will still be live even if you turn off the disconnect?

 

[Dennis Alwon]

Yes, you but you would need a disconnect for both voltages and they need to be clearly labeled and within sight. Is this a motor?

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.
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, provided that the 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 conforming
with Article 725, rated not more than 30 volts, and
isolated and ungrounded.

 

[Jraef]

Can you have a control cabinet with a 480 source to a disconnect AND a 120 source to the cabinet that will still be live even if you turn off the disconnect?

Certainly, it's done all the time. But depending on which standards apply, you must at the very least clearly identify that there are multiple sources of energy in the cabinet, and/or use a different color of wire to identify it (usually yellow), and/or interlock it via an aux contact of the 480V disconnect, and/or provide its own disconnect that is interlocked with the enclosure door. NFPA-79, which applies to industrial control panels for machinery, will require you to use one of the door interlocking options, plus the labeling and wire color.

 

[petersonra]

Can you have a control cabinet with a 480 source to a disconnect AND a 120 source to the cabinet that will still be live even if you turn off the disconnect?

yes. it is pretty common. how it is handled depends on the specific circumstances. you will still need some way to disconnect the 120V source. this is pretty common with industrial control panels where they want to be able to turn off the 480V power but leave on at least some 120V power for lighting and PLCs etc. usually it is done with what is called a lighting disconnect, which is a small box with a transformer, fuses, and disconnect that is wired to the line side of the main disconnect and supplies power for things you want to remain powered when the main disconnect is open. but sometimes they skip the lighting disconnect and just bring in a 120V circuit. same idea just implemented differently.

 

[Besoeker]

Certainly, it's done all the time. But depending on which standards apply, you must at the very least clearly identify that there are multiple sources of energy in the cabinet, and/or use a different color of wire to identify it (usually yellow), and/or interlock it via an aux contact of the 480V disconnect, and/or provide its own disconnect that is interlocked with the enclosure door. NFPA-79, which applies to industrial control panels for machinery, will require you to use one of the door interlocking options, plus the labeling and wire color.

Where we have had to use two different supplies they go through diffeerent terminal blocks. Those for the aux (safe supply) are shrouded and have warning labels.
And the panel itself has warning (yellow0 and mandatory(blue) labels.
See note 2 on the blue one - Remove all supply voltages.

I think it's incumbent on the responsible dessigner to take all steps in an effort to make equipment as safe as is "reasonably practible" and not limited to minimum codes or standards.