Control Panel Layout

Hi all:

I've undertaken the task of building control panels for the water/sewer utility at which I work. These are not UL panels, but do contain power supplies, PLCs, I/O, level controllers, HMIs, etc.

I'm wondering if there is some list of rules as to things like location of components and spacings between DIN rails and gutters, or if it is more of an art where the designer/builder makes these decisions on a case by case basis. I'm somewhat familiar with NFPA 79, UL508A and UL698A but these don't dictate these thing except for access and heat dissipation.

Do people just build a particular way because that's what they were taught? Does AutoCAD make certain assumptions/decisions?

I'd like to know I'm building the best panel that I can, as most of these will be nearly exact duplicates.

Thanks in advance for your wisdom and insight.


Curt Wuollet

From the variety I've seen, I don't think there are any rules.

I think the formulas are developed by trial and error, keeping the ideas that work well. Some are terrible, some avoid issues by simply making the backplane so huge that no finesse is needed to make things fit. Still others have the layout done so tightly there is no room to add another terminal or even pick up power and ground, no spare anything and even many instances of multiple wires in a terminal. You can learn from their mistakes. Find the panels you think look best and are easiest to work on and use them as examples. If you do a lot of troubleshooting you find the bad ideas quickly. A few spares and a little breathing room will be appreciated down the road. Remember these things sometimes last for decades.

A good starting point would be some of the various existing rules and regulations for electrical installations. For panels, we use the JIC standards for manufacturing equipment, essentially, the "american standards", probably outdated, but very useful. There are some rules of thumb obtained from panels built by others, validated by experience: Try to isolate internal panel wiring from that for installation, because you do not want anyone to interfere with your tested internal panel conexions, because, in case of errors, it can be easier to trace and fix. In other words, keep installation connections at the edges of the panel and include a wireway specially for the installation wiring. Locate heat producing devices in the upper part of the panel (power supplies, drives, transformers, an so on) leaving heat sensitive electronic devices at the botttom (plcs, amplifiers, etc.). In addition, never mix wiring trajectories of different kinds (power, control, instrumentation, low level signals) to avoid crosstalk and interference. In practice, this is easier said than done, but try to minimize it as much as possible. As for spacing, most manuals show general recommendations for spacing and location. If your panel room is tight, you might consider forced cooling. It all is dependent on your panel layout; keeping all of this in mind, you may get a decent working panel. I hope this helps.
I have never seen design aids.

Here's a few pet peeves of mine:

Always run DIN rail the whole width or height available. There's nothing worse than wanting to put in a couple of terminals and find the rail cut to just accommodate the original No of terminals.

Most panel shops seem to space the terminal DIN rail an inch or so from the backplane; this makes it easier to work on the terminals

Never use just one fuse for all the 24 Volt DC, break it up into groups of loops. Miniature breakers are better than fuses.

If you have a PLC consider using a separate power supply for just the processor. You don't want to reboot the PLC if there happens to be an intermittent short that pulls down the Voltage.

Different wire colours for 120 and 24 Volt wiring.

The different Voltages should be kept separate as much as possible.