How to deal with colour code conflicts? - Page 1
Forum section: electronics / projects

author: ironring1
author_rank: Newbie
timestamp: July 31, 2018, 06:57:52 pm
content: I hope that this is the right part of the forum for this question/discussion (if not, let me know)...I have a mixed AC/DC system that I am working on. This is for the company that I work for, and we ship products all over the world. Because I am in Canada, I use the Canadian Electrical Code (CEC) for the AC wiring (where I can):live = blackneutral = whiteearth ground = green (or green with yellow stripe)However, for my DC wiring, I also have a colour code that I am following:ground = black+5V = red+12V = orange+48V = yellowswitched version of a DC wire = white with a stripe of the colour of the signal that is switched (e.g., switched +12VDC = white with orange stripe)My problem is the clear conflict between the AC live and DC ground (both are black). I'm looking for suggestions on how to accommodate this issue. Here are some of the thoughts that I have on this:1) use red for AC live (this is compliant with CEC). I have no red wires in this particular design (no +5VDC in any of the looms), that just pushes a potential conflict down the road.2) stick with AC live = black, but route wires in separate bundles that are clearly labeled as "AC" or "DC", or clearly label the mains bundles as "AC Mains"3) Use AC Live = blue (in CEC, blue is the 3rd phase of a 3-phase system, so blue = AC Live is compliant), but in many other regions, blue = AC neutral, which could cause confusion for service staff overseas.I'm inclined to go with option 2, but if there are any other suggestions I'd love to hear them. Do any of you have good solutions to the problem of ambiguity with two colour codes that conflict need to be used side by side?

author: james_s
author_rank: Super Contributor
timestamp: July 31, 2018, 07:01:32 pm
content: Doesn't the electrical code only apply to building wiring and external power cords? As far as I know there are no requirements on the color coding of internal wiring inside equipment. Certainly I have seen equipment with all sorts of internal color schemes.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 31, 2018, 07:08:16 pm
content: 1 sounds dangerous - for example, over here, red is never used in mains voltage wiring, so it's easily associated with extra low voltage safety wirings, as it's averytypical color for ELV DC. I guess with each country, the same can be said for any color.I think there simply isn't a reliable way to indicate dangerous mains wiring over safety-voltage wiring just using the colors alone.So - choose #2. Be very clear about it - for example, "AC" is a completely wrong and irrelevant term to describe the "dangerousness" of the circuit, and while some people do misuse the term for that purpose (AC = dangerous, DC = safe), others may not understand it. Use graphical symbols and text such as "risk of electric shock". Use extra plastic covers whenever possible - this is for providing reinforced insulation between pri/sec as well, so these covers perform triple duty of giving you the redundant "double insulation", protect a careless service personell (including end users not qualified to do the job), and finally, offer a logical place to glue the warning sticker on, making it less likely to be removed.It's best if you can clearly dedicate a section for mains wiring / other dangerous stuff, so that the rest is all safe (think about the PC power supply)

author: JS
author_rank: Frequent Contributor
timestamp: July 31, 2018, 07:17:23 pm
content: Here the most standard live is brown, red and black are used in three phases mains. Neutral is light blue. In consumer products or any single phase installation leaves a bunch of colors to choose from. I like to use white for switched mains (or other mains color as black or red) in domestic installations, so when you find a light blue you know it's always live and when you find some other color you know it goes to a switch. But existing installations have all sort of mixed colors, I've seen some really dangerous like two green and yellow carrying mains and neutral, so I always check twice and go around with a voltage detector to see what's going on.JS

author: ironring1
author_rank: Newbie
timestamp: July 31, 2018, 07:19:13 pm
content: Thank you both. You right, James, that codes don't necessarily apply to chassis wiring, but I want the equipment to be as safe as possible.I was leaning pretty hard on option 2, and you right Siwastaja that "AC" is not in and of itself adequate for a label. Very good point. "risk of electric shock" or similar is a much better idea, as are internationally understood graphics/icons.

author: james_s
author_rank: Super Contributor
timestamp: July 31, 2018, 07:20:14 pm
content: IIRC in the US any color except for white or green is acceptable for live conductors. In domestic situations black is live, and red is used for the second live in 240V circuits and for the extra wire required by 3-way switches. In industrial 3 phase installations black, red and blue are commonly used for the live but other colors may be used. White is always neutral and green or bare copper are always ground.

author: tooki
author_rank: Super Contributor
timestamp: July 31, 2018, 08:09:59 pm
content: I’d consider using, for the AC stuff, the IEC standard of brown, blue, and yellow/green, because it really doesn’t have any ambiguity, since it’s colors that are never used in DC, nor in North American AC. This is what you see inside lots of stuff that’s sold worldwide. Above all, those colors are not commonly used for low voltage DC, so at least one would hope that someone opening the device might not assume “oh it’s red, that means 12V DC like in my PC.”

author: Hydron
author_rank: Super Contributor
timestamp: August 01, 2018, 01:54:42 pm
content: Quote from: tooki on July 31, 2018, 08:09:59 pmI'd second this suggestion (though am non-North American so am biased towards other systems).Mains colour coding seems to be a mess everywhere - in NZ it was historically (probably from UK) red for live, black for neutral and green for earth, now has changed to the IEC brown/blue/green-yellow standard for flex (appliance) leads but stuck with the old red/black/green-yellow for fixed (in-wall) cable. I suspect it's the same or similar in Australia, which tends to share these types of regulation. Unfortunately I don't think it's possible to come up with a system that avoids conflict between single-phase, three-phase and common DC colours given all the legacy stuff out there.On a similar topic, have you got any recommendations for a colour combination for 48VDC to be used in North America (USA specifically)? Should I avoid any particular colour or combination (other than green or green-yellow)?

author: Benta
author_rank: Super Contributor
timestamp: August 01, 2018, 03:01:46 pm
content: How about changing "DC black" to "DC black with white (or another color) stripe"? Black with stripe can easily be distinguished from your white with stripe scheme.

author: grumpydoc
author_rank: Super Contributor
timestamp: August 01, 2018, 03:16:47 pm
content: Quote from: Hydron on August 01, 2018, 01:54:42 pmIt was like that in the UK for a short while (flex following blue/brown/green-yellow with fixed wiring still black/red/green).Slightly better than in France where it is blue=neutral green/yellow=earth and anything you please for live. Red or black seem common as do orange and purple for switched or signalling live.Mind you I did swear a bit when I found a blue wire which was live when fixing the most obvious problems in the house I have in France - especially as that was before I replaced the broken RCD so got quite a belt off it. I swore even more when I found the green wire which was live as well

author: mtdoc
author_rank: Super Contributor
timestamp: August 01, 2018, 03:22:14 pm
content: Of those, I'd say option 2 is the best. That is how I've seen it done in North American market solar PV installations where DC and AC coexist. Another option I've seen is using green for earth ground to distinguish it from black for DC negative (though sometimes the two are bonded).

author: Hydron
author_rank: Super Contributor
timestamp: August 01, 2018, 04:03:20 pm
content: I think separate AC & DC bundles are probably a good idea regardless of colour scheme.No idea how accurate the linked chart is, but if it's even close then it shows how much of an mess things are:https://www.allaboutcircuits.com/textbook/reference/chpt-2/wiring-color-codes-infographic/

author: IDEngineer
author_rank: Super Contributor
timestamp: August 02, 2018, 04:10:44 am
content: Next, check out marine wiring. White is ground, brown is power, purple is switched power, and on it goes. Trailer wiring is similar."The nice thing about standards is there are so many different ones to choose from."

author: duak
author_rank: Super Contributor
timestamp: August 02, 2018, 04:28:47 pm
content: I worked for a company that produced for North American and later on, international markets. We ended up using IEC color coding for AC line (Brown, Blue, Green/Yellow) as UL/CSA was harmonizing with IEC (it's been years - IEC950?). DC wiring was to an internal standard, not all that different from what you've proposed. We were subsequently acquired by an international company and as a part of cost reduction and rationalization, all wiring was done with pretty much one color with numerical labels on each end where required. I see that most industrial equipment is now done this way.Personally, I like the idea & utility of power busses that are color coded. I also like the idea of properly labeled wires and easy to follow wiring diagrams. These definitely help the people that assemble, test and repair the equipment.Cheers,