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confusion with UL508A wire color recommendations
2

confusion with UL508A wire color recommendations

confusion with UL508A wire color recommendations

(OP)
Hi,

I have been trying to design an Industrial Control Panel that complies with the guidelines in UL508A. I am up to the point where I am choosing wire colors for the internal wiring in my panel. As my control panel will be used with industrial machinery, I am looking at the section of UL508A devoted to Industrial Machinery. Chapter 66 (Enclosures) recommends using black for all ungrounded AC or DC power circuit conductors. It recommends using red for an ungrounded AC control circuit.

The glossary in UL508A defines a power circuit as "Conductors and components of branch and feeder circuits". It defines a control circuit as "A circuit that carries the electric signals directing the performance of a controller, and which does not carry the main power circuit".

The incoming supply power for my control panel will be 208 VAC 3 phase (60 amps). It will have a VFD and Solid State Power Controller (for a resistance heater) that require 208 VAC. It is obvious to me that these are power circuits, so I will use black wire for these. I will also use black wire to supply 208 VAC to the primary of what I consider a "control transformer" (350 watt). The color to use for the ungrounded conductor coming out of the transformer secondary is less clear to me. This conductor goes to the line side of a 4 amp fuse (I'll call this F1 for the purpose of my explanation), which is the "main fuse" for my 120 VAC. From the load side of F1, I feed power to two smaller fuses (which I will call F2 and F3). F2 supplies power to my PLC, and F3 supplies power for the 120 VAC I/O that is monitored and controlled by this PLC.

It is very clear to me that all wires on the load side of F3 should be red, because (at least in my mind), they fall very nicely under the UL508A definition of a "control circuit".

It is less clear to me about the load side of F2 (powering the PLC). Should I treat this as a power circuit and use black? This is the circuit that powers the PLC (controller), but this PLC will just be directing the performance of what I consider the true power components in my panel rather than doing any "work" itself. If anyone here can suggest whether it would be more appropriate for me to use black or red for this circuit, I would greatly appreciate it.

I also have to decide what color to use for the line side of F1, and from the load side of F1 to the line side of F2 and F3, but after I come to grips with what to do for the load side of F2, I hope I will be able to infer what to use for these.

Any advice will be greatly appreciated.

Thanks in advance,
Paul
Replies continue below

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RE: confusion with UL508A wire color recommendations

No, all ungrounded wires after the control transformer would be red. Grounded (neutral) would be white, ground would be green.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: confusion with UL508A wire color recommendations

If you signed up and paid to be a UL panel shop then you could call your UL representative and ask them.

RE: confusion with UL508A wire color recommendations

(OP)
Hi JRaef and Lionel,

Thank you for your replies. I wish I had the budget to participate in the training that would be required to become a UL listed shop, but I do not. My company has recently ceased to manufacture new equipment. The specific project I have been asking questions about is to replace a 30-year old control panel that is in use on a machine we built in the 1990's. For all I know this might be the last control panel I design. I know it will not be subject to any electrical inspections because the machine is located in the same building I work in. It belongs to a sister company of ours with which I have worked closely with on many different projects. I am confident that my new panel will be safer and will work better than the old panel it will be replacing. I know it will work regardless of the wire colors I choose. After I had asked a question related to the disconnect I was planning to use, Lionel had pointed out that I should be paying attention to UL508A as this will be an Industrial Control Panel and the location is in the USA. Reading UL508A for this purpose sparked my interest, so I've been making my best effort to comply with its recommendations. Now I am in the very final stage of my panel design, where I have to select and order the wire and cable I need.

I really appreciate all the help I have received from you both, and from all the other members of this forum. If asking questions about specific codes (like UL508A) deviates too much from the intended focus of this forum, I will avoid posting this type of question.

If it is OK to ask this type of question, I do have a follow-up question after reading JRaef's reply. I will wait to see if it is OK before I post it.

Thank you again and best regards,
Paul

RE: confusion with UL508A wire color recommendations

Mr PaulKraemer (Electrical)(OP)7 May 23 21:07
UL 508A is not practised in my location (Singapore). My opinion is based on UL 508A 2nd edition December 20 2013 for your consideration.
....#1. that these are power circuits, so I will use black wire for these....
. Yes, colour Black.
#2..I will also use black wire to supply 208 VAC to the primary of what I consider a "control transformer" . Yes, wire colour Black.
No, this is NOT a "control transformer". But a "power transformer" see Fig 6.1. for more detail.
#3. The color to use for the ungrounded conductor coming out of the transformer secondary is less clear to me. This conductor goes to the line side of a 4 amp fuse (I'll call this F1 for the purpose of my explanation), which is the "main fuse" for my 120 VAC. From the load side of F1, I feed power to two smaller fuses (which I will call F2 and F3). F2 supplies power to my PLC, and F3 supplies power for the 120 VAC I/O that is monitored and controlled by this PLC.
All these are considered as Power cable.
Colour Black.
#4. It is very clear to me that all wires on the load side of F3 should be red, because (at least in my mind), they fall very nicely under the UL508A definition of a "control circuit".
No, these are "power cable", colour Black.
#5. It is less clear to me about the load side of F2 (powering the PLC). Should I treat this as a power circuit and use black? This is the circuit that powers the PLC (controller), but this PLC will just be directing the performance of what I consider the true power components in my panel rather than doing any "work" itself. If anyone here can suggest whether it would be more appropriate for me to use black or red for this circuit, I would greatly appreciate it.
These cables colour should be Black. Not red.
#6. I also have to decide what color to use for the line side of F1, and from the load side of F1 to the line side of F2 and F3, but after I come to grips with what to do for the load side of F2,....."
These cables colour should be Black. Not red.
Che Kuan Yau (Singapore)

RE: confusion with UL508A wire color recommendations

Che Kuan Yau - you don't know what you're talking about. Everything after that transformer is considered control.

We use a combination of red, black and white on everything after a control power transformer and have no objections from the inspector.

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