Instrument Signal Wiring Colour Codes

[Junior Designer]

Hello Everyone,

Can anyone please tell me if there is anything in the NEC or anywhere else (UL etc.) that speaks specifically to the conductor color codes for +ve and -VE of instrument signals (typically 24VDC/4-20mA)? I have checked but have been unsuccessful thus far. I know that in the US the accepted practice is Black +ve and White -ve. I have looked at UL-508A but it seems that it is specific for control wiring inside panels.
Also any reference to the accepted practice in Europe (White +ve Black -ve) would be appreciated since this difference is the at the root of my issue.

It's all a bit confusing and causes some conflict since there seems to be alot left open to interpretation. Any help would be greatly appreciated.

Thanks.

 

[cadpoint]

In the 08 NEC-70 on pages 70-686, 687,688 there is a list of Product Safety Standards.

The following might be one in the same as the page above but more might be found here on, UL's WP reflecting a search for; Home > Industries > Wire and Cable > Standards; all based on USA usage.

You might try going to UL's home page and signing is as being in Europe and see if you can find a page matching the one above, just a thought.

 

[tom baker]

250.119 would require the EGC to be green with a couple of exceptions.
White is the grounded conductor but when you work thru the rules, they don't apply under 50 volts.

White or Black to + or - it does not matter just be consistant.
You can also buy instrument cable with black and red.