UPS Wiring

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In regards to UL508A and NEC Article 409, is a power circuit from a UPS considered either a foreign voltage or non-disconnected voltage source and thus have to be wired with yellow wire? The UPS is for 120V and is contained within the control panel it is powering. The UPS does have multiple fused distributions of its power which can be used to disconnect this power source. These fused terminations are located immediately adjacent to the circuit breaker(s) used to provide a disconnect means for the control panel.
 

petersonra

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Northern illinois
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engineer
From UL508a:

d) Yellow ? ungrounded control circuits or other wiring, such as for cabinet lighting, that remain energized when the main disconnect is in the "off" position.

g) White with yellow stripe ? grounded ac control circuit current-carrying conductor that remains energized when main disconnect switch is in the "off" position.

I would say it is fairly clear that such wiring needs to be yellow to meet UO508a requirements.
 
UPS Wiring

The part of UL508a you reference deals with ungrounded control circuits. This is essentially a power circuit from an emergency backup source, complete with ground. As far a "main disconnect", in the NEC is not Disconnecting Means the proper definition with it being a device or group of devices by which th conductors of a circuit can be disconnected from their source of supply.? Is there a requirement to provide one, single device to disconnect all internal power sources?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
jkflipflop67 said:
The part of UL508a you reference deals with ungrounded control circuits. This is essentially a power circuit from an emergency backup source, complete with ground. As far a "main disconnect", in the NEC is not Disconnecting Means the proper definition with it being a device or group of devices by which th conductors of a circuit can be disconnected from their source of supply.? Is there a requirement to provide one, single device to disconnect all internal power sources?

There is no requirement to provide a single source of disconnecting means in UL508a.

30.3 Location
30.3.1 A disconnecting means shall be provided for each incoming supply circuit.
Note that this is not required to be in the cabinet itself. Only that it be supplied somewhere.

39 Disconnecting Means
39.1 A control circuit intended to be supplied from a separate source shall be provided with a disconnecting means that complies with Section 30, Disconnect Switches.

Note that the yellow wiring is clearly not limited to control cicrcuits, even if you considered the UPS output to be something other than a control circuit.
d) Yellow – ungrounded control circuits or other wiring, such as for cabinet lighting, that remain energized when the main disconnect is in the "off" position.
 
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