Hi everyone,

I don't know if this is the correct place to post but I couldn't find anything more appropriate.

I'm wadering if there is any guidelines for wire colours for low voltage DC? for example I have an assembly that will have 1V5; 3V3; 5V and 24V. Is there any standards or is the colour choice complete arbitrary?

Thanks,

 

No standard for colour codes, usually Red positive and Black negative, you can use Yellow, Orange, Purple, ..

 

Hello.

The answer to your question is “yes”, and “no”. There are standards for DC color codes but not for voltages, per se. For example the codes specified by the NEC and IEC are these:

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If I was going to color code based on voltage I would choose one of the standard and use a two-color wire that was mostly the L+ color but included stripes of some other color to distinguish. For example, red with white, red with blue, etc. and document on the device what the colors mean.

It used to be a common practice to glue a schematic to the case interior. It’s very helpful to include something like that.

 

thanks guys, the fact I couldn't easily find anything doing a google search made me suspect as much.

 

Hello.

The answer to your question is “yes”, and “no”. There are standards for DC color codes but not for voltages, per se. For example the codes specified by the NEC and IEC are these:

View attachment 294515
​

If I was going to color code based on voltage I would choose one of the standard and use a two-color wire that was mostly the L+ color but included stripes of some other color to distinguish. For example, red with white, red with blue, etc. and document on the device what the colors mean.

It used to be a common practice to glue a schematic to the case interior. It’s very helpful to include something like that.

Those are out of date. UK DC wiring colours have changed to red and white, to avoid confusion with AC cables. (About time too!)
I assume European ones have followed suit.

 

Where industrial control circuitry is used, Orange is used for any conductor that exists in an enclosure that is switched from any source other than the local enclosure disconnect.
IOW, possible to be live when the local disconnect is OFF.
Used to be Yellow for N.A. until it adopted the Orange International standard.
NFPA = White with Blue stripe is grounded/current carrying DC circuit conductors.

 

Those are out of date. UK DC wiring colours have changed to red and white, to avoid confusion with AC cables. (About time too!)
I assume European ones have followed suit.

dont suppose you have link to the UK specs please , my quick google could only find lots of "chatter"

 

I tend to use the ATX color codes for positive voltages and just wing it for negative voltages, signals and misc.

I'm in the US.

 

Bottom line. no standard, use what you like although it doesn't hurt to limit GND to black or green. But, anyone with experience knows, never trust the color, trust the meter display.

or as me daddy used to say: Electrons are color-blind.

 

Bottom line. no standard, use what you like although it doesn't hurt to limit GND to black or green. But, anyone with experience knows, never trust the color, trust the meter display.

or as me daddy used to say: Electrons are color-blind.

No, there are standards, just not for voltages. There are standards for ground, positive and negative, and two and three wire grounded systems.

 

dont suppose you have link to the UK specs please , my quick google could only find lots of "chatter"

My colleague has taken the 18th Edition of the Wiring Regs (amendment 2) home to study for his electricians' exam. I'll scan the relevant page for you on Monday. My cat is telling me he the 17th edition is out of date and needs to be ripped up.

 

No, there are standards, just not for voltages. There are standards for ground, positive and negative, and two and three wire grounded systems.

You are talking NEC/IC and AC/DC Power Systems wiring in residential and commercial.
TS is talking voltages within an "assembly" when he said " assembly that will have 1V5; 3V3; 5V and 24V. "
In the situation that he is talking... They are no standards for power wire colors within electronic assemblies such as TVs, Computers, Phones, etc.

 

If you want to feel good about picking something used before, then how about PC ATX power cable (pretty sure not a standard)
AND you get the honor of selecting the color for 1V5 (it looks like white is still available).

 

You are talking NEC/IC and AC/DC Power Systems wiring in residential and commercial.
TS is talking voltages within an "assembly" when he said " assembly that will have 1V5; 3V3; 5V and 24V. "
In the situation that he is talking... They are no standards for power wire colors within electronic assemblies such as TVs, Computers, Phones, etc.

That’s a good point, there is no de jure standard for internal wiring, but there certainly is a de facto standard for part of it. I would venture to say that black as 0V/Vss/-, red as Vcc/+, and green as ground/chassis/earth are almost universal and real should be stuck to when possible.

The TS situation of multiple voltages on wires is an example of why you might not be able to. ATX is OK, but it only offers 3V3. 5V, and 12V. Still, you could do worse than to use the scheme it does. 5V as the default Vcc makes sense and the others are arbitrary but at least there’s a logic...

Thanks for pointing that out.

 

I wish there was an internal standard for wiring colors.

This panel is a visual mess with feed color and internal color (tape on wire or wire) mismatches everywhere. Grey/Blue sometimes white neutrals, ....

 

Ok, so off topic,
but once worked for the now long gone Marconi,
their internal standard was every thing black
on basis you could never guarantee that some one had not modified the wiring with wrong colour cables.

 

That’s a good point, there is no de jure standard for internal wiring, but there certainly is a de facto standard for part of it. I would venture to say that black as 0V/Vss/-, red as Vcc/+, and green as ground/chassis/earth are almost universal and real should be stuck to when possible.

The exception to that is in control enclosures, where AC control voltage (120v/240v) BLK & RED is used in N.A.
For DC I always used Blue, +ve, and light blue for DC common.
Circuit wire ID markers were used at every termination point.

 

Ok, so off topic,
but once worked for the now long gone Marconi,
their internal standard was every thing black
on basis you could never guarantee that some one had not modified the wiring with wrong colour cables.

I also worked for the long gone Marconi!

 

I had a co-worker who became VERY DEAD because somebody had used white for a hot lead, 277 volts, in an industrial light fixture on a 24 foot ceiling. The shock zapped his heart and he fell off the ladder, breaking his head and neck. Certainly he made an error but did not deserve to die because of it.
And it certainly ruined my day!

 

I had a co-worker who became VERY DEAD because somebody had used white for a hot lead, 277 volts, in an industrial light fixture on a 24 foot ceiling. The shock zapped his heart and he fell off the ladder, breaking his head and neck. Certainly he made an error but did not deserve to die because of it.
And it certainly ruined my day!

I learned the moral of that story when I was starting out and re-wired my parents cottage.
Thought I had pulled the fuse, Pulled a pair of wires, one in each hand and got 240v (UK) across the chest, fortunately the shock made my hands jerk away.
But it stayed with me for ever!