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mjisaacs

...AND ANOTHER THING...

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I also have a customer that is prepping for AC FLASH compliance. They are installing interfaces for PLC connection on the outside of the cabs. They have only today, involved me in the process. They have purchased 1747-UIC w/ C13 cables and a cabinet mount jack for connection. The problem is, on two machines with SLC 5/01's, the DH485 (RJ45) jack is already used by an AutomationDirect EZ Touch panel. My question is, does AB make a "splitter" (for lack of a better word) for this situation, so I can be connected to the PLC while the HMI remains connected, all via the RJ45 DH485 jack?

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I had a Zycom touch screen & 5/01 . I split the signal with a AIC+ it worked OK for me. I just had to figure out the wiring layout and addressing. I am out of town so if no body else post it first I will post it Monday. Edited by JAK

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RS-485, if that's what you are truly using, is a "party line" system. Wire everything in "parallel" and you'll be fine. Usually you just do this right on the connector terminal block, same as with Universal Remote I/O and DH+. As to arc flash compliance...the end user MUST do the arc flash survey. I have yet to find a situation where the tables in 70E are actually valid. They usually tend to overkill but on a few instances, it's underkill (not good). Second, even 70E is questionable. It's roughly based on IEEE 1584 but I've run across instances where one gives a different incident energy level from the other, and again, EITHER one can give a higher value. In fact, I've read some literature that suggests that since the original data is based on averages of incident energy levels and not worst case, the energy levels calculated from either method are still not high enough. You really need to do a proper coordination study anyways and maintain it. If you have that and a little bit more information beyond it, doing an arc flash calculation is straightforward (with either method). It usually turns out that most people go grossly overboard simply because they don't understand it and follow NFPA 70E's "blind" recommendations blindly. That being the case, 24VDC is exempt (anything <50V is generally exempt) from the requirements. Best thing to do is put your power supplies in a separate enclosure or sub-enclosure and then your entire PLC cabinet is class 0. In my plant, it's a foundry, so our guys are already wearing class 1 stuff as normal workwear...we just needed to get the uniforms with the arc flash tags. Add a face shield and you've got class 2. Add a hood, rubber gloves, and a set of overalls and you've got class 4.

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...as have these guys. They are part of a large corporation that has decided anything is class 1, <50 is class 2, etc. As you said...overboard. My question only concerns the splitter for my PLC. They have already called in consultants that have decided the classes for them. I need a splitter that uses the RJ45 connections.

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Yes, the 1747 AIC will allow you to "tap into" the DH485 network without disturbing the HMI comms as long as your driver is set up correctly with a unique node number.

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Again, RS-485 is "party line". Everything can be wired in parallel. There's no magic splitter needed for what you are attempting to do. If you read the DH-485 information from AB, it is thoroughly confusing. So don't do it! Head on over to the Modbus site (www.modbus.org). Download and follow the wiring schemes for Modbus-RTU. The physical (cabling) specification for Modbus RTU is the same as DH-485 since both are RS-485 protocols.

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