control panel building

[Greg Dake]

40.) Remember "finger safe" for all 120VAC and 3 phase components as well.

41.) Arc flash rating and boundary information on the OUTSIDE of the panel, so individuals know the hazard and appropriate PPE to have on before opening the enclosure door.

42.) We've moved a lot away from 120VAC control, switches, lights, etc....and switched to a lot more 24Vdc components in panels. Also, keeping the control transformer outside the panel when possible, minimizing the 3 phase risk inside a control panel. We're trying to do more of this, I know it's not always possible.

43.) Best thing I ever did when laying out back panels : I take my pencil and start at the edge and mark every inch from right to left and from top to bottom. I then take my T-Square and make a giant 1"x1" grid out of the entire backpanel. Now all my measuring is done! Try it, it works very well. You also know what "level" is when the panel is not stading up. The 1"x1" lines work for the entire mechanical layout of the backpanel.

 

[stasis]

I can't believe that no one has mentioned this...Number/label EVERYTHING!! Try to make sure that terminal designations are linear. At the strip, the only time numbers should jump around is when separating voltages or power/controls. Also, on device positioning, try to follow the control prints. This helps keep a linear theme.

 

[Jimmie_Ohio]

When screwing down the duct, I place small plastic zip-tie tie downs under the duct screws. I may or may not use them all but they are dirt cheap and they are there. It beats trying to shove a stick-on tie down into a duct half full of wires.

Your list is impressive. However, I have a bit of criticism of the above info that actually has some significance in ampacity ratings.

First, I do not believe that it is common practice to tie wires in wire duct. Maintenance guys will hate you when they try to pull wires or trace them physically. (But we've all been hated for worse.)

Second, and more importantly, wire ampacity tables for inside control panels are normally rated as in "free air". The assumption is that the wires in duct are floating around with only about 50% fill (or whatever the max fill should be on wire duct). If you tie current carrying wires together, you impede the ability of the wires to stay cool. Now, you really should use ampacity tables for wiring in conduit, which may be up one wire size.

If you are conservative in your wire sizing, this point is moot.

 

[TConnolly]

I definitely second the suggestions on making the field terminals vertical. A vertical field terminal strip is much easier to connect than a horizontal field strip right next to the floor. The floor is rarely clean where the panel is installed, its hard, and its always cold. Which brings me to another suggestion:



Don’t sprinkle field terminals around the panel mixed in with terminals for internal use. Group al the field terminals together by type. Where possible I place discrete control terminals on one side of the panel and analog on the other side. Ideally, the field ducts are completely empty when the panel is shipped.



As I mentioned, I usually have a machinist friend do my door work for buttons and instruments, but if however you find that you are punching the holes yourself, then invest in a good set of punches. A high quality set of punches will have four lines scribed every 90 degrees on the circumference of the die. Using a pencil and a square carefully layout the grid on the panel, forming a large + where the grid lines intersect at each button location. Center-punch the intersection of the + and drill the hole. Then as you snug up the punch and die, make sure that all four marks on the die circumference are aligned with the grid lines. Now the punch and die is centered right over the button location.



Like Ron, I have dreamed of building a three axis table for drilling and tapping. But it will probably never happen, its hard for me to justify it. At one time I built all my panels. Now I build perhaps 2 panels a year (usually the smaller ones), the rest I job out. I’m fortunate to have the convenience of having a panel builder just half a mile down the street. He’s good enough that I’ve been known to just drop a pile of components off and trust him handle the layout without doing a CAD layout on rush jobs. (Actually, this guy has a really nice house with an attached 4 car garage – he has turned half his garage into a panel shop and he does enough business out of there to afford that nice home.)



Jimmy makes a point that cannot be overstressed. Follow the electrical codes.



Greg, I like the 1” grid idea. I’ll have to give it a try. I’ve got a little 24 x 40 panel coming up about mid December which I’ll do in-house.

 

[Jimmie_Ohio]

A high quality set of punches will have four lines scribed every 90 degrees on the circumference of the die. Using a pencil and a square carefully layout the grid on the panel, forming a large + where the grid lines intersect at each button location. Center-punch the intersection of the + and drill the hole. Then as you snug up the punch and die, make sure that all four marks on the die circumference are aligned with the grid lines. Now the punch and die is centered right over the button location.

Greenlee makes square punch/die sets in several sizes, even DIN standards. I bought those years ago and they are not cheap. However, if you weigh the cost of how simple it is to punch square holes versus having your employee screw up a door which leads to the following:

1) buy new door or weld filler in
2) repaint
3) re-punch
4) tick off customer because of delay
5) all costs of this out of your pocket

Now, these punches don't seem so expensive, do they? If you get at least one small square punch/die set, you can punch the corners of any size rectangular cutout, then just cut four straight lines linking them with a sabre saw. Any "hammer mechanic" can do this neatly.

 

[Greg Dake]

Alaric, let me know how you like the 1"x1" grid. I cannot express it's helpfullness enough in words....


Greg

 

[Rube]

Jimmie--

Wire ties don't have to be pulled tight just because you install them...

I put my wire ties on just like Alaric but they are for preventing wires drifting out of a duct, especially on a long horizontal duct. I sometimes cut the tie loose when I finish wiring.

Try it, I bet you'll like it

 

[Rick Densing]

I think Alaric has been watching me build panels, how else could he know all my great tricks?

37. Purchase wire retainers for the wire duct. Wiring a panel without them is a pain.

We use leftover 30.5mm PB gaskets.

 

[93lt1]

Jimmie--

Wire ties don't have to be pulled tight just because you install them...

I put my wire ties on just like Alaric but they are for preventing wires drifting out of a duct, especially on a long horizontal duct. I sometimes cut the tie loose when I finish wiring.

Try it, I bet you'll like it

I do the same thing, loosely installed wire ties in the wire duct for the only purpose of keeping the wires in the tray as the panel wiring is completed, It's kind of like a poor mans "wire retainer" mentioned by Tark above.

 

[TConnolly]

Good idea Rick. Like Mark, I would use loose ties as needed to just keep the wire in place - a must when the customer specs THHN wire instead of MTW. Then theres always those stubborn wires that just will not stay in place. When I have 'had it' with that wire it gets lashed to the back of the duct.

Also, if the spec calls for THHN wire, it has a lot less "spring" and lays better if you'll use it from 1000 foot spools instead of 500 foot spools.

Like Jimmy, I also recommend Greenlee punches. They are worth the money. I haven't needed to invest in the square punches, but then not everyone has a machinist with a big bed mill handy - and someday I might not either. Like Ron said earlier, its tools, tools, tools.

If you do a lot of button holes, then you should know that Greenlee makes a punch that will do the hole with four keyways for the anti-rotation tab on the button. I have one of those for 30mm buttons. I don't do many 22.5mm buttons however so I dont have one for those. I also have a punch for doing holes for d-sub connectors for RS232 ports - but I dont use that one much any-more.

I also install one of these on any panel that has a PLC in it.
http://www.asi-interconnect.com/products_and_solutions/interface_modules/remote_access_interface/ac_outlet_rj45/

 

[Jimmie_Ohio]

To clarify to "Rube" and "93lt1":

My earlier reply about wire ties in duct refers to the point that duct fill and ampacity of conductors MUST be considered. You can't just tell a wireman: "Don't pull them wire ties too tight".

Constricted wire bundling in duct, from an ampacity viewpoint, begins to look like wire in conduit, not "open air". Therefore, it must be rated as such.

As I also stated earlier, if you size wire conservatively and fill duct loosely, you have nothing in the world to worry about.

 

[Rube]

Cool...



...and I agree.

 

[BudW]

All of the above information is excellent it looks like it reflects many, many years of experience. Everyone would be wise to record it and keep it as a good, No an excellent reference.

25% spare space and terminals.

Here in the automotive industry the Auto Companies specifies it and the Automotive Engineers are good at dreaming up changes that will quickly fill up this spare space.

 

[MarkTTU]

25% spare space and terminals.

25% free space goes away quickly... I'd say in 25% free space in a panel lasts from 1-24 months most of the time.

 

[JohnW]

Control panel building is a bit fraught with pitfalls with regards to UK legislation. The key law is the Health and Safety Act and the main relevant regulations are the Supply of Machinery Regulations and the Provision and Use of Work Equipment Regulations. The main standards are BSEN 60439 (Low Voltage Equipment) and BSEN 60204 (Electrical Safety of Machinery) Before designing and building control panels make sure you are familiar with ALL the relevant standards of which there are very many. The HSE holds you responsible for the safety of your design for a period of 10 years. Also if you intend to sell you control panel in the EU it has to be CE marked ( another very large can of worms).

However a good practical guide to panel building is

Industrial Control Wiring Guide
Publisher Butterworth-Heinemann
Author Bob Mercer

RS part number 197-2079