PLC cabinet design

Hi guys.

I need design a PLC cabinet which will be used in USA. While I only have some experience of designing the cabinet used in China since I am a Chinese engineer. Is there any difference that I need to pay attention? Or is there certain US national code/guidelines which I can follow?

Any suggestions are welcome and thank you in advance.

I'd start with the National electrical code I know there are others but I'm not familiar with all the regulations in the states

Also NFPA 79.

We purchased a machine from China a couple of years ago. I am sure that it was not representative of all machines from China, there are some which meet standards, but in this case there was multiple issues with the electrical construction of the control cabinet. Shortly afterwards we removed the control cabinet and replaced it with one we had built.

Based on our experience with this one, some of the issues were undersized wiring, low quality terminals, poor documenation - I'm not refering to poor translation, we have Chinese employees so translation errors were solvable, but essential things missing from the prints, lack of wire numbering, components were jammed into a panel that was too small, and the panel itself was flimsy. The machine was shipped with a large tranformer that was un-enclosed with exposed high voltage terminals, that was the first change we had to make before we could even apply power. Over time we discovered that there were sevral wire terminations where two wires had just been twisted together, taped, and stuffed into the wireway - that won't be acceptable.

If you use good construction practices you can avoid many of the issues we had.

One thing to be aware of is that many IEC circuit breakers are only rated as supplemental protection in the US. Circuit breakers providing primary branch circuit protection must be UL489 approved.

The machine must be clearly labeled indicating manufacturer, power requirements (V, A, VA, number of phases, frequency) required breaker size, short circuit interrupt rating, electrical diagram numbers.

yfcarer

Ni hao

I agree with Alaric. I have supplied some controls equipment to China and have received some equipment from China. I also find some acceptable equipment and some that needed rework. Alaric already touched on some of the items that needed rework. The only other item that I can add, is wire color issues. There is code for what color wires to use for certian voltages and what style to use inside and outside of the enclosure.

Please see the below links for free Web viewable electrical code information.

NFPA 79
http://www.nfpa.org/freecodes/free_access_agreement.asp?id=7907

NEC (National Electrical Code)
http://www.nfpa.org/freecodes/free_access_agreement.asp?id=7005SB

I hope this helps
Bud

Code for wire color? I think there are "suggestions". I maybe wrong, please someone clarify this issue. But, I haven't read "code" for voltages. Please correct me if I am wrong on this issue. But I think it is more of a standard than code.

One of the EE's or Guru's may know more. I really dont want to lead one on astray.
Dog

But please clear up for me

NFPA 79 spells out certain colors for certain applications and reserves the use of certain colors for specific uses.

An excerpt from it can be accessed here.

Check your work properly, then you will have no problem.

- use ferrules, and crimp with a good crimpingtool
- use some kind of core marker, that follow your drawing
- when finnish, arrange and dress cables so it looks neat and tidy
- any high voltage things shouls have protektive cover

etc.

And on top of all of the above, you have to conform to the specs of your customer as well. We (here at GM) have our own way of doing things that is clearly spelled out. Be sure to check with your customer first.

and also check how the client want grounding to be done, some dont care at all, and others want separate groundbars for IE and PE.

Thank you very much guys. Your experience is very helpful to me.

You are right. I will have a careful read about your links, keep your mentions in my mind and establish a frequent communication with our client.

BudW said:

yfcarer

Ni hao

I agree with Alaric. I have supplied some controls equipment to China and have received some equipment from China. I also find some acceptable equipment and some that needed rework. Alaric already touched on some of the items that needed rework. The only other item that I can add, is wire color issues. There is code for what color wires to use for certian voltages and what style to use inside and outside of the enclosure.

Please see the below links for free Web viewable electrical code information.

NFPA 79
http://www.nfpa.org/freecodes/free_access_agreement.asp?id=7907

NEC (National Electrical Code)
http://www.nfpa.org/freecodes/free_access_agreement.asp?id=7005SB

I hope this helps
Bud

Click to expand...

Thank you so much!

I work on a lot of Chinese machines and find a lot of problems. Color code is the most (green is ground). Prints don’t match wiring (have to chase wires) Open terminals (not enclosed). Wrong type of fuses or circuit protection. Motors under size or when they get stuck stop and no O/L trip. And my most favorite 380-volt motors hooked to 220 and wonder why the loss of torque and trip breakers.


Call the UL people to get the cabinet UL listed and they will tell you what to change or update.

If this is a one up then it might not be worth it but if planning to sell more in US might look into it.

Also reference the Industrial Control Panels standard, UL 508A.