MicroLogix 120 VAC digital input wiring

[Epy]

Before I fry a 2nd ML1400, I figure I'd confirm my wiring assumptions.

I have a 1766-L32AWAA (120VAC logic). On the digital input side, there are 20 inputs and 4 common terminals. I have neutral connected to all 4 commons, and am trying to test the input by connecting line/hot to one of the inputs. This is correct, right? I fried a previous one with this wiring, tried it again just now to only see nothing happen.

Common always means negative/common (DC) or neutral (AC), right?

 

[bce123]

Common always means negative/common (DC) or neutral (AC), right?
NO!
IN THE CASE OF INPUTS IT DEPENDS if they are sinking or sourcing
most outputs common are what ever you intend to send out

 

[Bullzi]

That is how I wire up AC inputs. I fried one too when I was testing it out. The next one I got, wired it the same and it was fine. I think I might have gotten metal shavings into the PLC when I mounted it. That is the only reason I can see for it to short out like that. Anyone else have this issue?

 

[Mickey]

See picture below.

Sounds like it should work. What exactly is not happening that you think should?

 

[Epy]

Well, I should be seeing the first input square fill on the little LCD itself, and should see the I:0/0 bit turn to 1, correct?

And yes, that's exactly how I have it hooked up, except that everything is coming from the same source, i.e. all L1s are the same line, and all L2s are the same neutral.

Where did you find that wiring diagram? I didn't see that in the installation instructions publication.

 

[Mickey]

See link Chapter 3 page 37

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1766-um001_-en-p.pdf

 

[Mickey]

Is the processor in the run mode?

 

[Epy]

Yes

 

[Lancie1]

I am trying to test the input by connecting line/hot to one of the inputs.

Make sure that your test wire is really connected to 120 volts (HOT) and not the neutral. Neutral will not do anything for you.

Is it possible that you have the two 120 volt power feed wires swapped at your PLC power supply terminals? That could cause you to get them mixed up. Check to see which wire measures 0 volts to Ground. Hopefully, that is your Neutral or L2 conductor.

 

[Epy]

0V to ground for neutral, 119V to ground for hot.

Would an incorrect connection elsewhere on the PLC nullify the inputs like this?

 

[Lancie1]

Only an incorrect connection on the Input terminals or the Input "L2" terminals could cause the inputs not to activate.

You do have to have SOME type of program running in the PLC, don't you? Even if it is just a blank or empty program, it still must run to allow the PLC to stay in RUN mode. You have to be in RUN mode with no FAULT indicator showing. If your MicroLogix 1400 goes into FAULT mode, then all bets are off.