Compactlogix and 1734-FPD

Hello,

I have a Compactlogix 1769-L18ERM-BB1B and I'm adding 3 120vac I/O modules. Two 1734-IA4 input modules and one 1734-OW4 output module. Do I need a 1734-FPD between the plc and the 3 modules fed with 120vac?

Thanks for your help!

YES !

It's very good that you asked; this is a good opportunity to take a look at the 1734 Selection Guide and be sure you understand all the wiring diagrams.

All of the network adapters and CompactLogix controllers that use POINT I/O feed the field power bus (the two slide connectors closest to the bottom) with 24V DC. If you were to connect an AC module, you would back-feed the controller with 120 V AC and let all the smoke out.

The 1734-FPD Field Power Distribution module's whole mission in life is to separate and isolate the Field Power Bus.

Now that I got the bold red out of the way, a couple more comments:

The 1734-OW4 has only eight terminals, so it can serve those four relay contacts. They're all isolated from one another, and do not connect to the Field Power Bus.

The 1734-OW4 passes the Field Power Bus right through. You could connect more 120V AC modules to the right of it and use the same field power.

When you read the Installation Instructions (1734-IN055I) for the POINT Relay modules, you will see example wiring diagrams that show the old DeviceNet 1734-PDN adapter. Don't be mis-led by the fact that they show the Field Power connection coming from AC power... the 1734-PDN was the exception to my statement that "all" network adapters supply 24VDC. The -PDN got its logic board power from the DeviceNet plug, so it was able to allow any voltage to be applied to the Field Power bus.

And one more before I go.

The 1734-L16 and -L18/L19 controllers have a power input connector with separate inputs for the controller's control power and the Field Power bus.

On the very first models, you actually had to provide a separate power supply just for the logic control, and another for the FP+/FP- input terminals.

Series B and later controllers (what you'll certainly be buying) allow you to use a single bulk power supply if you wish.

I provide logic power and I/O power with separate fuses, so that a short in an I/O circuit won't necessarily take down my CompactLogix. And sometimes I provide the +24V Output power via an emergency stop circuit, depending on my application.

Lots of good info, thank you Ken! I've been reading about this a couple days now and just wanted to make sure I understand correctly. From what you say I think I'm the right track. Thank you.

I had my distributor do the BOM for an upgrade I'm doing and the FPD was not on the list. They also sold me 12 pin terminal blocks but I don't really need that many for my modules. Will this affect anything?

I don't like to second-guess distributors, but if they saw 120V AC modules and didn't quote a 1734-FPD, you need to review all the choices.

When building a POINT I/O system you can use the Rockwell product selection tools like Integrated Architecture Builder, or the manuals themselves. For POINT, you always need both to Selection Guide and the individual Installation Instructions (these have the wiring).

In general, POINT I/O modules use the 8-terminal 1734-TB terminal bases.

The 1734-TB3 terminal bases have 12 terminals, with several connected together (4-5-8-9 and 6-7-10-11) for more access to the Field Power Bus.

A quick look at the 1734 POINT I/O Selection Guide shows that the 1734-IA4 and the 1734-OW4 modules both require the ordinary 1734-TB terminal blocks.

A look at the 1734-IA4 Installation Instructions then shows that the top 4 terminals are for the four 120V AC inputs, while the bottom four terminals are connected to the L1 (hot) side of the field power bus.

I don't think you can use the 1734-TB3 twelve-terminal block with the 1734-IA4. I'm not sure what would happen if you did !

Is the "upgrade" you mentioned the same as the CompactLogix and IA4 + OW4 ?

I'm totally second guessing them.... I work with older technology like the slc500 stuff.. so that's why I'm looking for advise on this newer hardware. Now that I understand what field power is everything makes sense now.. We checked resistance on the output module and 2 of the outputs are connected internally. So I'm thinking that's because of the 12 pin module base...

All the parts in question here are part of the upgrade I mentioned. I'm upgrading an obsolete servo system. So the project consists of the the Compactlogix and I/O modules mentioned here and 2198-P070 DC Buss supply, 2189-ERS3 servo drive and a MP Servo motor.

The 120vac modules are signals like Start Index, Jog Fwd, Jog Rev and a safety circuit. And I need to send signals back like Index Complete and Drive Ready, ect...

While trying to understand how to wire the modules I got a lil confused and that brought up other questions, like the FPD, and module bases.. so that's what brought me here to ask.. I'm sure glad I did.

CRC83 said:

The 120vac modules are signals like Start Index, Jog Fwd, Jog Rev and a safety circuit. And I need to send signals back like Index Complete and Drive Ready, ect...

Click to expand...

Wouldn't it be a good idea to use 24V for these pushbuttons and lamps instead, then you'd be able to dispense with the FPD

This is part of a machine I'm upgrading so all pushbuttons ect.. are existing components. It's an older machine so everything is 120vac.. some signals are actually coming from an SLC500 rack.

The old servo system had it's own display/ keypad, controller and inverter. The SLC500 supplied the Start, System Auto and a couple other signals. I asked my supplier for the hardware needed to upgrade. Now I'm just trying to make it all work. 24v would make things easier I believe but that would require a lot of rewiring...