View Full Version : SLC 500 -1747-L20 AB Fixed Controller Guide

December 19th, 2005, 01:21 PM
I have no prior experience in this PLC field, and I'm hoping to get some help in powering up Allen Bradley fixed controller.

1)Is there any specific manual other than SLC 500 Fixed Hardware Style Controller that might help me wiring it up?

2)What is the difference between VAC Neutral port and AC COM port on the controller?

This is my first assignment for my internship. I hope with some help from the experienced here I could impress my boss :)


Ron Beaufort
December 19th, 2005, 01:36 PM
you can save yourself a lot of time, trouble, and possibly some "magic smoke" by telling us up front exactly what catalog processor you have ... (example: 1747-L30A) ... secret handshake: different models use different voltages and different wiring diagrams ... and welcome to the forum ...

PS edit ... what type of communication device do you have? ... example: 1747-PIC or 1747-UIC or ??? ... if it's a PIC, do you have a real-live old-fashioned serial port on your computer? ... or an adapter? ... and do you have RSLogix500 already installed and ready to go? ...

December 19th, 2005, 01:37 PM
try this link


December 19th, 2005, 01:53 PM
if that don't help the AB website has the manuals on all the components so you should be able to find what your looking for on there.

December 19th, 2005, 03:17 PM
Ron: Sorry, I thought I already put up the right subject of the top, thats why I didnt mention it again in the msg. I have Allen Bradley 1747-L20A Fixed Controller, with RSLogix 500 software installed to my computer. Also I recently bought a 1747-UIC cable for downloading/uploading from PC-to-controller. I got to play with the demo unit which has SLC 5/02 Modular Processor with HHT before but that one is all wired and ready to be programmed. But this one comes in lose no power no I/O wires connect to it.

Keldog: I'm still studying that diagram you sent, and do you know what's the difference between AC COM and VAC Neutral? Seems like they both should be connected together.

Appreciate all the responses.

December 19th, 2005, 03:30 PM
You'll want to hook the hot wire of your 120VAC cord to the first screw. Should be labeled 120/240 VAC. The neutral of that cord gets hooked to the VAC NEUT. The AC COM screws are the AC commons, with regard to the switched AC inputs to the PLC, which basically gets jumpered to the VAC NEUT terminal.

Study the wiring diagrams closely in the back of that SLC500 fixed processor manual. Find the one that pertains to the 1747-L20A.

Just a forewarning, keep in mind that only certain option cards will work with these fixed SLC500 units. Likewise, only certain instruction in the RSLogix500 will work with the fixed processors.

Ken Moore
December 19th, 2005, 03:42 PM
I'm still studying that diagram you sent, and do you know what's the difference between AC COM and VAC Neutral? Seems like they both should be connected together.

The VAC Neut connection is for the Processor power, your unit is designed to run on either 120 or 240 VAC (85-265).

The inputs however, are only rated for 120VAC (85-132).

So depending on the situation, the AC Com and the VAC Neut may or maynot be the same.

Look at this clip from the wiring diagram:

December 19th, 2005, 03:45 PM
VAC Neut is the main power into the PLC PS, AC com, is common, it can be hot, neut, or gnd, and most importantly it is at least one protection device deeper than nuet, meaning there is a fuse or circuit breaker on the hot leg. Yes nuet will tie pretty much directly to neut but the wires in the panel will usually change color, from blk and wht, to all red or all yellow or either color and white depending on the panel builder, if you see blue and blue w/white stripe or white w/blue stripe those should be DC.
Now that you're even more confused, have fun.

December 19th, 2005, 03:51 PM
Is this what you are seeing? If so yes it could be connected to the same AC neutral that powers the PLC...if the input power is coming from the same source.

This manual may provide more info: http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1747-um009_-en-p.pdf