USA low voltage wiring standards (Festo PLC)

Nortech

Member
Join Date
Mar 2018
Location
Spain
Posts
59
Hi All,

I have a project at the moment with a Festo PLC to be sent to the states. It must adhere to UL standards which I am not familiar with. From research I think I should be using Red for 24vdc, Black for 0vdc and white for ground. Is this correct?

Can anyone else offer any advise for US wiring standards?

Thank You.
 
Wiring standards for industrial machinery are covered in a standard called NFPA 79. NFPA is the National Fire Protection Agency, they also publish our National Electric Code (NEC) which is NFPA 70. All of their standards are available at NFPA.org.

But to your question, UL doesn’t care about wire colors so long as you properly identify them, but these color schemes are what you would find in NFPA 79:
DC should be blue,
AC Controls should be red,
AC Line Power should be black,
white is reserved for grounded Neutral
Ground is green or green/yellow.
 
Last edited:
Your customer has the ultimate word on this but it is most common to use black for AC circuits 200V and above; red for 120V AC line, white for 120V AC neutral and green for ground.

As far as DC circuits, in many cases it will be brown for DC+ and blue for DC-
 
I use:
AC Line power :Black
AC Control:Red
AC Grounded Neutral :White
Ground:Green with Yellow Stripe
DC 24+: Brown
DC 0V: White with Blue Stripe (Blue with White Stripe)
DC Control: Blue
 
I use Yellow for Live AC Coming from a source that is not disconnected with the Disconnect on the panel ( I have seen Orange used) And must be labeled in Panel. These are typically interlocks from other equipment.
 
+1 for a different color for interlock circuits plus we add a label, (tag) on the enclosure that will state not all circuits entering/leaving this enclosure are de-energized when disconnecting this panel or something to that effect.
 
look up nfpa 79, electrical standard for industrial machinery, and nec 70 - electrical code book, nfpa 70e - arc flash.

there are others, but I don't know your system.

things designed for 50 hz typically burn up in 3-6 months un the USA (personal experience), so get things designed for 50/60 hz.

our electrical outlets are 120 volts ac, not 230 volts.
we also have 220, 440 volts, as well as others, not 380.

I don't know about your location.

james
 

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