Positive Ground

I am currently quoting on a project that specifies positive ground. Also says sinking 24vdc inputs and sinking 24vdc outputs. This is going to be using a SLC 500 with ethernet. Is the card needed a 1746-ib16 input card and a 1746-OV16 output card? Also, can anyone enlighten me as why they want it this way. This is backward to what I am used to, especially the positive ground.

I hope this will help
http://www.automationdirect.com/static/specs/sinksource.pdf
Regards,
Neeraj

Alot of ships use a positive ground system.

I've also come across it in old cars such as vintage jaguars and old British motorcycles - in this case its like all the old British stuff ... because they could.

As to ships - I have little knowledge apart from it may have something do with corrosion resistance (like how they protect steel pipelines with low voltage cathodic protection systems.)

A 1746-IB16 input module has its common terminal tied to ground, and receives "a more positive" signal (+10 to +30vdc) to indicate an "ON" condition. So with a positive ground, if an input wire touches ground, the input point in the card will go true.

Be wary of the terms sinking and sourcing and carefully determine what those occasionally mis-used terms are in refrence to.

I would definitely want to know what type of sensors (NPN, or PNP) are to be connected and the loads also.

You will wnat to draw up some example circuits and scrutinize what will happen when an input wire shorts to ground, and how that fits the application.

Do you want a false input? Or do you want to blow a fuse or fault a DC power supply?

There are tons of posts on the subject, and many experts wathcing new ones, so you may get the best answer just by expanding on what is specified in the ciruits vs. what you must design, and a little more about the application.

Paul

I'm new to the world of different grounding systems... but you'd think positive ground could be dangerous if it came anywhere near a actual earth ground?

This is also not uncommon with diesel generators. Had one unit where the main frame was negative ground and a control PCB was positive ground - checked the main frame first and decided the whole thing was negative ground - connected to the PCB and there was a big bang.