We are working for Russian construction project. According to our Russian partner, wiring methos for 24V DC instrument such as transmitter, solenoid valve, gas detectors, etc. shall be 3-wire system (+/- and earthing). As far as I know, the 3-wire method is very old Russian practice and it is not valid any more. Therefore we understand that europian style 2-wire system (+/- only) is sufficient for 24V DC instrument wiring. Also as far as we checked, we have never found out such code&standard requirement of "3-wire".

Good luck finding anything on Russian Codes. I spent a few months trying to track down High Voltage information last year with no luck.

You probably will have to get your Russian partner to produce a copy of their code. If they can't try to discuss a solution based on what you know about European standards.

From what I have heard about problems with Code enforcement in Sakhalin you might be screwed.

P.S. If you do get hold of actual Russian wiring code feel free to post it!