Reply To: Controllogix – Controller sizing/IO cards/Power questions

CajunconfiguratorSean Terrell
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I would certainly be wary of using 120VAC fo the control system. I am not sure where this system is to be installed but many PLC Programmers and Controls Tech types are not Licensed Electricians. Many states required a license to work on voltage of 120VAC and this will mean your contractors and installers need to be as well.

I know that there are many different components that rockwell offers, and I am not totally sure of your application however, I make it a rule to always use the 24VDC High Density I/O cards for DI’s and DO’s then drive 120 or whatever voltage I need using Relay’s or if I have 120 coming back from the field, use an interposing relay to switch back down to 24VDC. Also High Density I/O is not often a huge difference in price, and makes a difference down the road when you need “JUST ONE MORE DI” for some crap management has decided they want to see of the SCADA. Literally been the song and dance for the last 2 projects ive done, and the answer was to add a RIO to add on the one more DI and 2 DO’s. Just something to consider.

This also makes building the panel easier, as all of your field wiring can be brought into terminal blocks and shop testing / FAT is much easier.

However, rockwell has alot of tools including the Product Selector that you can utilize or call the Tech Connect number, they can give you 100% of the engineering limitations of any piece of hardware.