24VDC industrial wiring - Protection

[Bachman]

This is the first forum I've seen dedicated to the CEC, it's nice to see.
Is there a code in the CEC that encompasses the proper fusing of 24VDC industrial circuits. How do I determine the proper fuse size for PLC input cards and PLC output cards. I've seen it done many different ways. I've seen it were each card gets individually fused, I've also seen a group of cards protected by 1 fuse. What's the right way as far as the code is concerned? Also which current rating of the card should I be using to determine the protection? For instance a very typical AB output card #1746-OB16 has the following specifications:

Load current(min): 1mA
Continuous current per point(max): 1A
Continuous current per module(max): 8A

I suspect that I would use the continuous current per module. And so, do I fuse the card at 8A or do I also have to mulitply it by some factor?

Thanks, Bachman

[bigrockk]

Hello Bachman and welcome to the forum,
As far as code goes I don't believe it is going to be very specific as to how you fuse the I/O'S .
I quickly did a scan through the "book" to see what might pertain and a few I came up with are: Section 14 P.85 has a section on fuses. Other rules that may apply are 14-402, 14-414,14-608, The section on solid state devices on P.89, Maybe section 16, or 26-000 and 26-140.
These are just the rules I came up with on a quick look through the CEC I am sure there are more rules that apply.

I have never installed any PLC's but did maintain them (Allen /Bradley) and their associated equipment in the past. If I remember correctly the input module had no fuse and the 8-point output module had a 6-amp fuse. I think the max current per output on "our" system was 1.5 amps per output but only 6 amps max for the module.