Request a Re-Write of the Wire Color Rule for 2013.

[Tristan Lall]

I believe FIRST was responding to non-North-American teams which were having trouble finding wire that did not comply with IEC 60445 (which is described in rough terms here).

Incidentally, this thread has prompted me to go track that standard down for another project, so if I find a copy at the library, I'll verify whether FIRST's rule is consistent with it. (If I read that linked chart correctly, our systems are unearthed DC, not negative-earthed DC, so grey, not blue should be reserved for negative. But I'd rather double-check the definitions before making any conclusion.)

I wouldn't say this is at the top of my list of rules that need to be taken out back and shot,¹ but it has issues like no exemption for custom circuits (even COTS ones like fans), and odd consequences like when someone combines +12 V and +5 V to get a +7 V output with an unusual voltage reference (they're both red wires).

¹ Bumpers.

[Al Skierkiewicz]

Scott et al,
The color codes (and ampacity specs) are taken from the NEC (National Electrical Code) and the European equivalent of the NEC. In past years the rule had stated the color codes were for PD branch circuits so that sensor wiring was excluded.

[FrankJ]

The standards are some what conflicting.

IEC likes Blue for zero volts. The NEC likes blue for non zero DC volts. A good many panels in the US will use Blue for +DC & Gray or Blue with white stripe for 0V. The AC parts of the NEC call for white for neutral or grounded conductors & Black for non grounded AC conductors (Highly simplified). In DC Black for zero volts & Red for positive is pretty universal. Except Black & White twisted pair is really common for shielded control wires. Some plants like using black for the 0 V which makes white positive. Others use white for O V (It is the "neutral" color) which makes black positive (hot). The DC 0 V often gets grounded somewhere in the plant, making the black wire the grounded conductor. (A big NO if you are on the AC side of building wiring.) The take away here is unless you are somewhere that is really rigid about following one standard: you need pay attention to where the wire is going in addition to the color of the wire.

I would like to see the rule for wiring colors relaxed for multi conductor cable going to sensors & other low power items. The 2012 rule still requires the sensor supply wires conform to the color code. I can see still requiring the color code to be followed on single conductor wire.

[JDL]

There really is no good existing standard for FIRST to copy. The NEC, UL 508, NFPA 79 all are mostly AC centered. With the NEC we can basically use anything but gray, green and white for our ungrounded "hot" AC conductors.


For FIRST I'd like to see something like red for +12, blue for +24, and yellow (or similar) for +5, and black for all negative conductors. Conductors in cables should be allowed to be re identified if you want. If you want to identify negatives per voltage twisting, tyrapping, lacing, labeling, taping (either "phase" taping the negatives or using tape to bundle) would be optional.


No matter what the color code is though everyone should get into the habit of using a meter to confirm. One of the first thing you learn in the real world is once maintenance guys get at it and contractors guys start applying WIT (What's In the Truck) all bets on color are off.