Very basic wiring question-3 wire AC prox to 1746-IA16

I finally have my test/learning bed set up at home. I understand logic and programming, there are some holes in my basic electronics knowledge, however I do plenty of wiring on 480v at work, replacing sensors, relays, troubleshooting panels etc.

My lofty first goal is to have a sensor hooked to my SLC500 and be able to do exciting things like wave my hand in front of it and have a light turn on, maybe for a number of seconds, or maybe with a delay, or maybe as long as the sensor is triggered, you get the idea. I am looking at this as a hobby for now, something else to play with in my workshop, while also hoping it helps at work in the future.

So please forgive the very basic question....

I have applied line and neutral to my sensor on the bench and monitored the voltage between the third wire and the same neutral the sensor is plugged in.

Id have expected the third wire to either have 120v on it or not, however it seems to always have 120v regardless of the indicator light on the prox.

Aside from that perhaps....my basic question remains this:


How to wire the sensor to my module.....
the module is a 1746-IA16. There are a number of "IN" terminals and two AC com terminals.

I suppose one of the sensors wires would go to an "IN".
What about the other two wires? What is AC common on the module? Is that a "line" to power the sensor?

There are two commons marked at the bottom of each row of input terminals...so each "common" is for all of the terminals above it? multiple sensors, etc?

Any responses are greatly appreciated!

The 2 commons are internally connected. Is it possible that you have got ahold of an NPN proximity switch? A part number could help to direct you which wire colors or pins to connect to what.

On AC Input modules, you connect the "Common" to the "Neutral/L2" of the connected AC source.

The 1746-IA16 just has two AC Common terminals for convenience; as noted by others they are internally jumpered.

There's a good wiring diagram in the Installation Manual for discrete SLC-500 I/O modules.

https://literature.rockwellautomation.com/idc/groups/literature/documents/in/1746-in027_-en-p.pdf


If you have a 3-wire AC sensor, you typically connect "L1" or "Hot" to one wire, and "L2" or "N" to the other.

The third wire is the switched output.

120V solid state circuits always leak a little bit of power, just a few milliamperes. Input circuits are built to burn off that power and only react to a 120V signal at above a few milliamperes.

When you connect that output signal wire from the sensor to the 1746-IA16, you should be able to measure 0V or 120V at the terminal, depending on the state of the sensor.

Ken Roach said:

If you have a 3-wire AC sensor, you typically connect "L1" or "Hot" to one wire, and "L2" or "N" to the other.

The third wire is the switched output.

Click to expand...

I was picturing this when I mentioned NPN. I do not working with AC proximity switches ever really. After looking around 3-wire does not look to be that common for an AC proximity switch, the ones I came across that were 3-wire are combo N.O/N.C. So 1 wire is power and 2 wires would connect to two inputs, input card provides the common neutral for the 2 switches in the prox right? should likely work with either 1 of the 2 wires, so you could chose N.O or N.C. going to the PLC card.

Edit: Maybe possible the 3rd wire is GND?

I'm finding the same thing as Snyd1... If you have a NO/NC switch, its already shot.:angr: (Maybe) ... But check the documentation which comes with the switch...

Thanks guys. I have so many irons in the fire right now, I havent got back to it yet. Ill give your suggestions a shot!

Snyd1 said:

I was picturing this when I mentioned NPN. I do not working with AC proximity switches ever really. After looking around 3-wire does not look to be that common for an AC proximity switch, the ones I came across that were 3-wire are combo N.O/N.C. So 1 wire is power and 2 wires would connect to two inputs, input card provides the common neutral for the 2 switches in the prox right? should likely work with either 1 of the 2 wires, so you could chose N.O or N.C. going to the PLC card.

Edit: Maybe possible the 3rd wire is GND?

Click to expand...

There are 3 wire AC proximity switches out there. Two wire switches are more common, but I've definitely used 3 wire AC prox switches as well.