In section 66.5.3, the UL508A standard lists the following
color coding for internal power wiring.
Black - all ungrounded control power circuit conductors
regardless of voltage
White or natural grey - grounded AC current-carrying power
circuit conductor, regardless of voltage
In section 66.9, the UL508A standard lists the following
color coding for internal control wiring.
Black - all ungrounded control circuit conductors operating at the supply voltage
Red - ungrounded AC control circuits operating at a voltage less than the supply voltage
Blue - ungrounded DC control circuits
Yellow - ungrounded control circuits or other wiring, such
as for cabinet lighting, that remain energized when the main disconnect is in the "off" position
White or natural grey - grounded AC current-carrying control circuit conductor, regardless of voltage
White with blue stripe - grounded DC current-carrying
control circuit conductor
White with yellow stripe - grounded AC control circuit
current-carrying conductor that remains energized when the
main disconnect is in the "off" position
The UL508A standard does not apply to wiring outside the
industrial control panel.