Lets talk building control panels

[ashesman]

I hope this topic doesn't already exist, I couldn't find one so...

I was hoping people could post hints, links, parts and pictures of how they build control panels, what are their goto parts and any interesting hints and tips.

For example, what material do you use for back plates? What size panel trunking is preferred? MCBs vs fuses? Cooling options...

[cncsnw]

1) Make sure the enclosure is large enough, so that the components are not jammed together, or up against the wire ducts and walls; and so that you have room for adequately sized wire duct.

2) Plan your layout with an eye towards the "low voltage, low noise" zone (e.g. PLC inputs, encoder signals, communication with PC and jog panel) and the "high voltage high noise" zone (especially servo drive output power and VFD output power). As much as possible, segregate your wire ducts and pathways so that noisy wiring is not mixed with noise-sensitive wiring. AC control wiring (120VAC and 24VAC at 60Hz) can generally mix with either category, though I do try to keep the 120VAC that powers the computers away from the servo and VFD outputs

3) I typically use steel subpanels from the enclosure supplier. Aesthetically, I prefer the white painted ones, but that does mean you need to clean off the paint in places where you want positive bonding. Automation Direct sells the subpanels separately, so if you are adding one to an existing enclosure, it is usually not hard to buy one that will fit.

4) I mostly use 40mm wide by 60mm high (1-1/2" x 2-1/4") wire duct. On small projects with limited space and not too many wires, I use the 25mm (1") wide duct, of the same height. For trunks carrying more power cords and cables, I use wider duct. Changing the width, but not the height, makes the junctions neater.

5) Now that miniature UL489 circuit breakers are readily available (e.g. Eaton FAZ-...-NA breakers), I usually use those. Previously I would more often use class CC fuses (for any motor/power loads) or class M fuses (for control circuits). I mostly avoid glass fuses.

6) There was another thread recently about cabinet cooling. If you use fans and outside air, make sure:
a) That the fans blow in (positive pressure)
b) That the air comes in at the bottom and exhausts out near the top (convection is your friend)
c) That the entry filter is effective and serviceable (oil mist, welding smoke, dirt and metallic fines are not your friends)
d) That the exit filter/screen is effective (flying chips are the main concern here)
For particularly harsh environments, consider either a heat exchanger or an industrial air conditioner.

[BodeRacing]

Use galvanized back panels. Don't use painted. Painted back panels are a capacitor, and believe it or not can affect electronic reliability. Galvanized panels also allow for much better grounding. Painted back planes should never be used for any electronic equipment.

All variable speed drives should have a shielded motor lead cable (including servo drives) properly bonded at both the drive back panel and the motor to provide a low impedance common mode current return path. Even with a shielded cable, you should maintain 3 - 6 inch separation to all other cables. If you don't have a properly shielded motor lead cable properly bonded on both ends then 12 inch separation from all other cables should be maintained.

These are best practices for electronic reliability when drives are used.

[ashesman]

Painted back panels are a capacitor

I am interested to hear more on this. Any two conductors separated by a dielectric are a capacitor. There is a potential scenario where if something with a conductive frame is bolted to a painted back panel that there is capacitance between the panel and the component. But if the mounting screws of the component conduct then the capacitance would surely be negligible?

[BodeRacing]

Painted back panels are a capacitor

I am interested to hear more on this. Any two conductors separated by a dielectric are a capacitor. There is a potential scenario where if something with a conductive frame is bolted to a painted back panel that there is capacitance between the panel and the component. But if the mounting screws of the component conduct then the capacitance would surely be negligible?

You would think so, but that is not always the case. Back in the 90's when I just just learning about stray currents, ABB educated me on effectiveness of ground planes versus ground wires and that painted back planes are a capacitor and that is one reason that electronic equipment mounted on galvanized panels is more reliable than on painted panels.

Remember that the stray currents we are dealing with from a drive are typically 1 - 2 mhz, but can also be higher. The mounting hardware has significant inductance, hence not all that effective in shorting out the capacitance especially with large panel surface areas. In an industrial application, maybe 50 hp or so motor, I measured almost 30 volts p-p between the motor and gearbox - both mounted on a common steel base plate. That is because of the inductance of the steel base plate.

In the 90's we were dealing with large drive systems that kept blowing up. Had painted back planes. One thing we ended up doing is fixing all the ground bonding connections to the back planes. We ended up either grinding the paint off or using star washers. We quantified each connection using a digital low resistance tester. It helped drive reliability.

Marketing folks don't like galvanized back planes because they ain't as purty as painted white back planes...........

[tblough]

All that may be true, but open the electrical cabinet of any Maho, Makio, Hurco, Haas, Hermle, Okuma, Mazak, Hardinge, Tsugami, etc. and I'll bet you see a painted back panel. Somehow, they make them work in spite of the "Marketing folks".

[JasonPORC]

I am by no means an expert, but I've been using Automation Direct for several years after buying my first VFD to run my Lagun Milling machine in my home shop. I like their website, and they've always had quick shipping and great customer service.

McMaster is also great.

That all being said, I've been so delighted to find a few local electrical distributers that are amazing! They almost always have a few long term employees who've forgotten more about what I'm asking than I will ever know. If you've nice, and want to pick their brain, most often times you can learn a ton. They've also got me hooked up with other related companies. (a great bearing shop, motor rewinds, spindle rebuilders, etc) I like supporting local if at possible, and during Covid, buying local really is a life saver for some. Just my 2 cents. Cheers.

[BodeRacing]

All that may be true, but open the electrical cabinet of any Maho, Makio, Hurco, Haas, Hermle, Okuma, Mazak, Hardinge, Tsugami, etc. and I'll bet you see a painted back panel. Somehow, they make them work in spite of the "Marketing folks".

That's all great till you get gremlins that cause the system to misbehave either in a failure or just odd behavior. It also helps in long-term equipment reliability.

This is a best practice, and when starting from scratch its just as easy to use galvanized instead of painted.

If you look at equipment coming out of Europe, its all galvanized inside. This is because of EU/IEC regulations for emitted noise. They got it right and later on the drive manufacturers figured out how much the galvanized structures helped in drive reliability. It was a side benefit from the original directive.

One time I went to help a plant that printed CD covers with reliability. They had 5 lines and only one was reliable. Opened up the reliable line cabinet and it was all galvanized inside because it came out of Europe and none of the other ones had any galvanized panels. And then there was that new super fancy good looking Fanuc robot that was failing at least once a week. Open the cabinet and it was all painted on the inside and significant high frequency voltage drop across the component enclosures in the cabinet. I have many examples where it was just a bad idea to used painted back planes, and even more on improper drive installation...........

I have been in many countries around the world solving stray current problems including France, Russia, Poland, New Zealand, Brazil, Portugal and several I probably forgot about...............

[martyscncgarage]

Well, I use a sheet of 5052 aluminum for my back panels. Has a protective skin I use to mark on, drill/tap through....
Then peel it off, stuff the panel and get to work....no problems so far...?

[martyscncgarage]

Marc, you panels are immaculate...
Marty