Connecting Different Equipment

If I have a PLC in machine A and I want it to give an input to machine B then I want to trigger an output in machine A based on the condition and Fire a relay that will close contacts and deliver power sourced from machine B to Machine B PLC input.

This works well for us for PLC's that don't have compatible communications but MY question is what's the best place to put the physical relay? I assume Machine A but then I have to mark that power from another source is in that panel when the disconnect is off. I have to mark the panel like that either way because if I put the relay in machine B when the disconnect is off it could still have live power from machine A if the output that fires the realy is energized.

What is the best placeemnt method?

Relays in machine 'B'. use the lowest voltage practical, e.g. 24VDC for coil. If more than one group them together. In panel 'B' place a separate shield over the relays with its own sticker indicating voltage. And of course mark the outside. The runs from 'A' to B' in their own conduit or at least low voltage conduit.

This keeps the higher current (and more noise resistant) cables running from machine to machine.

Ether way you do it you would have to mark 'foreign voltage' somewhere.

Prosoft can help with dissimilar communications protocols if you want to make stuff talk..

the cheapest solution would be like you described with a relay. You could run the control power from machine b through an aux. contact of the disconnect on machine a to ensure all sources of power are killed when the disconnect is off.

you could also throw in some remote I/O in machine A and the only thing you would need to run to machine b is a comm cable and remote power sources would be a non issue

As mentioned above the use of a relay for one or two discreet I/O points is the norm, anything above that, you should look at some type of module based I/O, if Allen Bradley this can be Block, Remote, Flex or Point I/O or a Mircologix mini PLC. The module I/O can be connected via DH+/RIO using a twin axial cable (Blue Hose) which has a clear, blue and drain /sheild, or Devicenet (red,black,blue and clear, drain/sheild), or Controlnet (coax Quad sheild) or Ethernet (cat5e/6) or Sercos (orange 2 channel fibre, I highly doubt you would be to this step), theres also other modbus based comms aswell. The comms would depend in the end how much you want to spend, what you have around the site (existing) and the speed of communications required.

I'm not sure what the codes are in the USA, for separating sources, but in Canada as long as machine A and B are under one roof, then you can place the relay box anywhere that's easy to access, it just has to be tagged / marked its power feeds are from (2) different sources.

Make sure to RED Line the electrical drawings, that you added in the aforementioned JB, otherwise the maintenance guys will eventually get caught not knowing this phantom j-box exists and it could lead to alot of downtime, confusion and safety issues.