Posted by: Harold Ennulat | May 13, 2013

Control Panel Layout And Wiring Best Practices.

Control Panel Layout And Wiring Best Practices.


Large Control Panel Wiring Example. What are some good practices?  What could be improved? Click to enlarge

Large Control Panel Wiring Example.
What are some good practices? What could be improved?
Click to enlarge

The quality of the wiring methods used in an industrial control panel can vary quite widely.  This article summarizes what this author believes are some best practice when it comes to control panel layout and wiring.

The goal is to produce a panel that is logically arranged and easy to maintain for the life of control panel.

I leave it to the reader to use these suggested “best practices” outlined below to evaluate and improve upon the control panel designs that they encounter or are part of producing.


  1. Wire:  Use all 600V 90 Deg C rated wire.  Use stranded wire.  Use MTW type wire.  Note any exceptions so these can be added to the drawings or design notes.
  2. WiringAcrossAHingeBestExample1croppedWiring across a hinged door or panel.  U loop, as long as possible, facing down anchored on each side of the hinge with screws or bolts (no adhesive). Place sleeve or spiral wrap over the wires running over the hinge between the anchor points.
  3. Spacing between wired devices and wireway or other obstructions:  2″ minimum; 2 1/2 – 3″ preferred for 120VAC and less.  4″ for 480 volt (enough to insert a closed fist between the device and the wireway or obstruction.
  4. Minimize the use of cable/wire ties if wire duct is used.  They get cut off when troubleshooting and are rarely replaced.  A good wire management system should not require any wire ties.  Make it a goal to use no wire ties except temporarily while wiring.
  5. *  Leaving Slack:  Generally, leave only “hidden” slack.   Leave service loops as the wires leave or enter the device or terminal.  Run wires in the wireway so they enter and run to the middle or far side of the wireway or duct.  Take all corners in a wiring duct as wide as possible.   Run wires in horizontal and vertical lines.  This also adds further “slack” and improves the appearance.  Avoid looping wires in the wireway unless the wireway is designed for this.
  6. General Wire Routing:  Run wires in horizontal and vertical lines, no diagonal runs.  “Train” the wire by bending it to make neat vertical and horizontal lines.  Delicate wire will require “training” by bending and forming the bend gradually.  Wire in wire duct should be run so they do not cross each other excessively.  Wire entering or leaving a wire duct should be brought to the front of the duct before entering/exiting where possible.  Leave service loops and run wires in the wireway so they enter and run to the middle or far side of the wireway or duct and take all corners as wide as possible.  Do not run wire over other devices, including the wireway.  Elevate the duct and go under the duct with wires if needed.  Review needed exceptions.
  7. Wiring Power And Motor Wiring:   Place Pig tail loops between devices that are spaced such that it makes it easier to remove wiring if the pig tail is added.  Consider using High Flex power wires such as “Railroad Wire” or high strand count wire.  Train the wire by bending it in the direction you want it to go or lay in the duct, rather than just trying to lay it in a wire duct and hope it “stays down” in the duct.  See also “General Wire Routing”.
  8. Wiring Signal and Shielded Cables:  Use 18 AWG shielded, twisted pair (or Triad) type cables rated at 600V as the default signal wire type.  Unless specifically required strip off a generous amount of the jacket so that each conductor can be easily accessed for removal, testing, and replacement.  Also remove the jacket as it exits a wire duct, keeping the twists where the cable otherwise creates unwanted wire congestion.  Examples:  going to Analog I/O modules, or routing to elevated side terminals.  Terminate all shields.  Terminate all shields close to the signal wires.  Consider using 2, 3, or even 4 high terminal blocks with jumper slots for signal wiring depending on the wiring needed.  This allows busing the power supply voltages for a cleaner installation.  Option:  Place heat shrink tubing 1/2 over the cut end of the cable jacket and 1/2 over the exposed wires.
  9. Wiring Control Wires:  Use 14 AWG 600V MTW (stranded) wire for 120VAC wire.  Use 16 or 18 AWG 600V MTW (stranded) wire for 24VDC wire for up to 10 and 5 amps respectively.  Use “General Wire Routing” recommendations found elsewhere in this document.
  10. Terminations:  leave some bare wire showing to allow visual inspection and to avoid screwing down on the insulation.  Wires should exit the terminal straight. Do not bend the wire at the point of termination.  Instead loop or bend wires on the insulation that do not go straight to the wireway.
  11. Terminals:  Screw Terminals: Use tubular, pressure plate type screw terminals that minimize wire distortions or damage when terminating.  Position Terminals to allow visual inspection of the recessed connections.  Elevate Control Terminals to allow wiring under the terminals if needed.  Keep it stiff using a heavy-duty DIN rail or Hoffman Terminal Straps or equivalent.  Angle and elevate terminals mounted on the side panel for wiring ease and to allow visual inspection of wiring in the terminals.
  12. Grounding  Principle:  Wire all grounds to the incoming ground lug either directly or with a wire to the other ground bus bars.  Add a main ground lug and/or a ground bus bar for each grounded power supply.  A number of busbars can be utilized but should all be wired together and then to the incoming ground lug to at least 1 point if not two (2).  This is in addition to the ground established through the panel.  Use 2 ground wires from opposite ends of the bus or chain of ground bars if the ground is isolated.  Wire the ground on all doors and subpanels and the cabinet itself to a ground bar terminated at the main ground lug.  Wire all equipment and chassis grounds to the ground bar(s) which is terminated at the main ground lug.  For additional details on grounding and bonding see the Grounding And Bonding post dedicated to just this subject.


Example of good spacing between the terminals on the wireway.

Example of good spacing between the terminals and the wireway.

  1. Optimize the Space.  Place PLC I/O racks in the “bay” created by the wiring duct to allow room for the high density of wires going to them from the duct.  Don’t leave space where there is no wiring, typically the top of the I/O rack.  Place similar sized devices in their own “bay” where possible.  Consider the routing of all of the wires and how the various voltages will be kept separated.
  2. Spacing between wired devices and wireway or other obstructions:  2″ minimum; 2 1/2 – 3″ preferred for 120VAC and less.  4″ for 480 volt (enough to insert a closed fist between the device and the wireway, another device, or obstruction.


For additional information on control panel design see the list of Control Panel Design Posts on the picture panel at the top or at the link here.


 |  Created: 5/5/2013 3:30pm CST; for Publishing on 5/13/2013 at 5:00 am CST



  1. […] Downloads The top link might be most useful – Technical guide – Control panel – Panel design Control Panel Layout And Wiring Best Practices. | Harold On Controls…protection.pdf Reply With Quote   […]

  2. As a controls engineer with past experience in panel building I appreciate your tips for good wiring practices. Especially the one about eliminating wire ties inside raceway. It makes troubleshooting a lot easier if you don’t have to cut 20 wire ties. I am having some trouble with a recent hire in our panel shop (an old guy good at his job but set in his ways) and was wondering is there were any regulations restricting their use in raceway? He will listen to that. I looked in NFPA 79 but found nothing.

    • I’m not aware of any regulations. The reason I published this article is as a result of seeing the various and sometimes imaginative practices used by panel shop wiremen. If nothing else it lets them know what I consider to be a best practice and generates some discussions that usually ends up improving the resulting panel fabrication.

  3. the information is very helpful thank you

  4. Very Good Info. I’m a test engineer and I see many companies that just seem to not know what it mean to practice good wiring habits. You didn’t address the EMC part of panel wiring. Conducted and Radiated Emissions should be a concern when it come to good wiring practices. Perhaps I missed it.

    • Here in the states we aren’t as concerned about EMC unless we send a panel outside of the US and to Europe especially. Actually the article only covers wiring. It doesn’t address any type of added componentry or special wiring techniques for specific installations. However, I would think that these wiring practices would still apply if EMC filters and other measures are added.

      Thanks for your comments.

  5. We do worry about EMC in the states. But because of the harsh PPE requirements for mixed panels, we generally separate low voltage controls from noisy ac devices without thinking about it. Sometimes I cannot avoid mixing quiet (AKA clean) and noisy (AKA dirty) signal wires/components, and in such cases I designate clean and dirty wire ducts by using white and grey respectively. I also prefer to use only current for analog signals as these are less effected by noise than voltage analog signals.

    The rule of thumb for DC wiring size: This is generally fine, but when there is an inductive control suck as a solenoid or relay, the wire needs to be sized to handle the inrush current. I’ve seen people undersize the wire based on the holding current which can cause a relay to pull excessive amps and burnout well before its life expectancy.

    Another item worth noting is that it’s considered best practice (and may even be a code requirement) to lay a panel out so that power flows from top left to bottom right. Generally the disconnects are at the top. In european panels, it’s different. It goes from bottom to top and I think it’s also inverted so that it goes from right to left but I can’t remember.

  6. I’m not aware that wire needs to be sized for inrush as wire is sized to keep it from overheating. Wire is sized to handle voltage drop so that when a device draws inrush current the voltage doesn’t drop below the solenoid or relay pickup point. What is the basis for the statement about relays burning out because the wire is not sized for the inrush. Motor wiring for example which can draw large inrush currents in the range of 7 – 13x FLA is only sized for 125% of FLA (full load amps). See NEC code book section 430.22 (2011 edition).

    As for power flow it depends. A logical arrangement is helpful however.

  7. thank u for da gud info

  8. Spacing between wired devices and wireway or other obstructions: 2″ minimum. Is this a must? As im used to leaving only 1.6″ which is 40mm in my panel desings.

    • Just a number that allows wire access with at least one finger and thumb. I find that 2″ gets tight for my fingers which aren’t that fat. This is why I like to get the spacing between 2.5″ and 3″ for 120VAC and lower voltages.

  9. This information is very helpful.

  10. This is some really good information about automation panels. It does seem like a good to look at the terminals. I know that I wouldn’t want to worry about having issues with the control panel.

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