Control panel building

[mavrick]

Hello,
I would like to build a control panel to house a some controls for a small system at work. Probably will install small PLC and couple contactors for motor controls, drive, etc. This will be my first control panel build and would like to know if there is information on building one. Such as the NEC for electrical but for 24 volt controls.
Anything from sizing 24 volt power supply, what to fuse off PLC (outputs, analog, etc.)
Any help would be appreciated. Thank you

 

[seth350]

NFPA 79 has much of what you need to know.
NEC will instruct you on wire sizing and protective device sizing.

Being it’s your first one, and at your place of work. You might ask if there are any certain standards the company insists on having.

If they are lax about it then read up on NFPA 79 and NEC. Mike Holt’s site is also very helpful, although most topics may lean toward the residential side. Good information nonetheless.

Stick with UL listed stuff and don’t use self-tapping screws to attach your components to the backplane. Not allowed according to NFPA. Drill and tap for a 10-32x5/8” Phillips pan head machine screws.

Rule of thumb for me is to leave 2” above and below terminal strips, breakers, motor starters, overloads, etc.
Refer to manufacturer recommendations on spacing for drives, PLCs, reactors, brake resistors.

Keeping that in mind, you can layout your panel on paper or CAD and leave yourself plenty of room for “oh ****, I forgot about...” moments.
If you ain’t sure if the box will be big enough, then it won’t be.

And for the love of all things good in this world, don’t use wire duct that is less than 2” tall and less than 2” wide. Smaller wire duct that has its place and purpose when needed.

 

[James Mcquade]

use the following.
Nec 70 national electrical code
Nfpa 79 - electrical standard for industrial safety
Nfpa70E - are flash - this is becoming a big issue.
NFPA 496 - standard for purged and pressurized enclosures. for use in hazardous environments

since you have motor contactors, nfpa70e will be needed. basically you put high voltage power, contactors, drives in this panel. 120 volt controls in another panel, and 24 volt in another if possible. over simplification so read up.

before starting on the panel design !! GET LOTS OF DETAILS!!
what is the area classified as? normal area, gas, dust, fiber
if its a hazardous location, different rules apply.
what chemicals / fumes are in the area?

NEVER EVER sacrifice safety due to pressure from the customer or the boss !
it is your career and reputation you are putting at risk.
if you do, it can come back on your company and they will put the blame on you. hat to say this, but it's true.


ALWAYS allow for spare terminals, plc expansion, lots of spares, someone always forgets something or wants to add something.

TO AVOID a mess, work with the mechanical designers to see what they are planning. what hydraulic valves, pumps, pneumatic valves, reed switches, sensors they need. ask why. this is from personal experience of 30+ years.

AGAIN, NEVER sacrifice safety !

lots to throw at you, best of luck
james

 

[mavrick]

Thank you for the help. I'm not sure I would be able to separate the voltages. Because I will be using 480 volt to power my motors. Also I will need 24 volt to pull in my contactors and 120 volt to power my 24 volt power supply. Any ideas will be appreciated. Thx

 

[seth350]

If all you need 120V for is to power your power supply, you could opt for a 3ph 480V power supply.

Although 120V in the cabinet is handy for laptop power. Your preference.

Adding to what James said about separation of the voltages...
Basically, with arc flash standards and the gear needed to just open a live panel that is operating above 50V, it is much more preferable to separate the voltages into their own cabinets. So when you only need to check the PLC (if it’s being powered by 24V and 24V I/O), you don’t have to suit up in your arc flash PPE.