The Black wire should be negative DC return in 4-20mA loops

[mbellow]

Hello, in another forum I posted thread196-248328. I believe a discussion is also need here.

John wrote that "It is common for 24 VDC 4-20 mA loops to use black and white pairs, typically with 24 VDC source on the black wire. Black and red is also used.

I would like to say that in over 27 years it has only been over the last few years that people have tried to promote using 'Black' as positive DC voltage and not as the negative DC return as it has traditionally been.

In asking around and reading comments, I believe that this trend is due to using electrical engineers for the designing and electricians to wire systems up and not instrumentation engineers and technicians.

What color is the negative (return)wire going to the DC battery in your car and used in American produced electronics?

Comments are requested.

 

[dpc]

It's just a convention either way. I don't think it is terribly important as long as there is some consistency within a particular facility.




"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

 

[JLSeagull]

See my response in the duplicate post under ISA:

http://eng-tips.com/viewthread.cfm?qid=248328&page=1

 

[DRWeig]

I have to pitch in with "doesn't matter" from my perspective, since it's signal level stuff. Consistency within a system is required, as dpc noted.

In my business, we build custom panels by the thousands each year for our customers -- according to their specs.

What I see is that they tend to stay completely away from black, red, and green with signal wires. These they typically reserve for DC power buses and safety ground. They tend to get creative with signal wire colors, but stay consistent.

There are exceptions, but this is the overall view.

Good on ya,

Goober Dave

 

[mbellow]

It does matter. I agree, consistency is key. However, when you 'bid' out jobs, unless there is a standard to follow, you will have differences with installations. If 90% of what a technician works on, Black is negative and someone installs a few that have White as negative, problems will happen.

I agree that in 'panels' wiring is different. The are that I am specifically addressing is field cables; CLX, Shipboard Marine cable, used for current loops.

I have a question and concern for panel builders concerning mA loops. Where would be the best places to post it?

 

[DRWeig]

mbellow,

A good place to reach a bunch of panel builders would be in the UL forum. Lots of 508A shop people there.

Glad you're here!

Goober Dave