The project group are going to install a new plc rack above the current cpu rack. New I/O is required and there are no slots available.

The project group were going to install 14 year old PLC hardware as a costs saving as well.

I have requested that they move the current rack 0 and 1, up and insert the new rack underneath to maintain a logical order.

Is there any standard from ISA, ISO, IEC or IEEE that will help my position?

 

There is no pressing engineering reason to maintain a logical order in the racks - it's a "nice to have".

However, depending on the details of the existing arrangement, changing the order could mean rewiring the existing rack. This then introduces the likelihood of a slew of issues with wiring of the existing racks, as well as those that arise from the new work.

If the "new" hardware has been sitting in storage for 14 years, there could be some nice problems sleeping in them just waiting for a bit of voltage to be applied before coming to life - specifically any that arise from dried-out electrolytic capacitors. If that's likely, I'd be far more concerned about making sure the equipment gets a proper check-out under live conditions than about the rack order.

 

I see no benefit to moving the old rack. Its a lot of work for no reason and there is a strong potential to have some kind of wiring mishap in doing so.

I am not a big fan of adding obsolete I/O to an older system, but if that is all that is available to work with the system as is and they have decided to use the old PLC, maybe that actually makes some sense.

I would think this is the time to look at upgrading to a more modern PLC and/o I/O system, but maybe they looked at the whole situation and decided that was not cost effective.

--
Bob
http://ilbob.blogspot.com/

 

In 30 years, I have never encountered a blind or illiterate PLC technician.

If the techs at your plant can see and read, wouldn't a label on each rack, something simple along the lines of Rack 0, Rack 1 or Rack 2, eliminate the mystery of which rack is which?