Socket Color Coding

[br4n_d0n]

I've been trying to figure out why some companies such as Rohde & Schwarz use Blue for the negative sockets on their equipment. I've searched a bunch of standards and cannot find anything definitive unless I overlooked something. I even sent Rohde & Schwarz an email close to a week ago, but no one ever responded. I also found out from my searches that the Black and Red "standard" here in the U.S. is not really a standard.

If anyone has an actual reason, please share.

[srb1954]

I've been trying to figure out why some companies such as Rohde & Schwarz use Blue for the negative sockets on their equipment. I've searched a bunch of standards and cannot find anything definitive unless I overlooked something. I even sent Rohde & Schwarz an email close to a week ago, but no one ever responded. I also found out from my searches that the Black and Red "standard" here in the U.S. is not really a standard.

If anyone has an actual reason, please share.

In my part of the world it was common practice in telephone exchanges to use blue insulation on wiring from the negative pole of the exchange battery. R&S may still be following this old telephony colour coding scheme.

[rdl]

For many years, maybe from their beginning, HP used red for both positive and negative. It wasn't until just before becoming Agilent that they changed the colors.

[David Hess]

Old Tektronix power supplies used green for negative, black for common, and white for ground.

[br4n_d0n]

Seems like no one really knows... 

It would've been nice if they responded to me so I could get a definitive answer

[tooki]

The only answer I’ve been able to find is posts saying that it never was a specific standard. It’s just convention.

There are a few (competing, contradictory) standards like IEC and NEC now. But they’re really for wires in permanent installations, not for bench use.

For what it’s worth, in my own projects (as in, inside things, not lab stuff), I use the ATX power supply color code if possible.

[Kim Christensen]

Maybe the guys at Rohde & Schwarz are were once EU electricians... Blue is neutral in the EU.
Sometimes, like in North America, where you see 12V DC wiring where Black is positive and White is negative. 

[nightfire]

In Germany, usually the live wire in AC is coded brown or black, neutral is blue. And since some serious change in standards in I think the 1970s, earth is not red anymore in installation, but 70/30 green/yellow, whereas the percentages are allow to vary but must not exceed whether 70% or be below 30% of the coloring of a wire...

And in DC in germany usually red is the +, black or blue are -.

These things are valid for small devices, installation and machines with their wiring cabinets have some extended standards for their appropriate coding of circuits.

[EPAIII]

All I can say about that chart is,

Oh My Gosh!

The only answer I’ve been able to find is posts saying that it never was a specific standard. It’s just convention.

There are a few (competing, contradictory) standards like IEC and NEC now. But they’re really for wires in permanent installations, not for bench use.

For what it’s worth, in my own projects (as in, inside things, not lab stuff), I use the ATX power supply color code if possible.

[tooki]

All I can say about that chart is,

Oh My Gosh!

The only answer I’ve been able to find is posts saying that it never was a specific standard. It’s just convention.

There are a few (competing, contradictory) standards like IEC and NEC now. But they’re really for wires in permanent installations, not for bench use.

For what it’s worth, in my own projects (as in, inside things, not lab stuff), I use the ATX power supply color code if possible.

In what regard? (I didn’t create the color code, nor did I create that table. It’s just a convenient one I found online.)

[br4n_d0n]

And in DC in germany usually red is the +, black or blue are -

Sadly, this is probably the closest I'll get to an answer

[james_s]

And in DC in germany usually red is the +, black or blue are -

Sadly, this is probably the closest I'll get to an answer

What were you expecting?

There was never any sort of legal standard for the color coding of terminals on test equipment, there have been various conventions that have been used over the years but nothing to force compliance. It could be as simple as the particular engineer that designed the device chose colors that they liked. Small details like that are often lost to the sands of time.

[wasedadoc]

For many years the British standard colours for single phase AC mains fixed wiring and appliance cords were red:live, black:neutral and green:earth.  After joining the EU those were changed to brown, blue and green-yellow respectively.

[themadhippy]

  After joining the EU those were changed to brown, blue

About 30 years after  we joined ,whilst harmonisation was the main reason red green colour blindness was also often quoted as a secondary reason for the change

[tooki]

For many years the British standard colours for single phase AC mains fixed wiring and appliance cords were red:live, black:neutral and green:earth.  After joining the EU those were changed to brown, blue and green-yellow respectively.

Which is completely irrelevant to the question because those standards are for AC, not DC, and for mains installation, not test equipment.

[themadhippy]

Which is completely irrelevant to the question because those standards are for AC, not DC

wont be irrelevant if your bit of pre2004  kit chucks out 2 phases and neutral when your expecting to see a nice plus and negative DC supply

[rdl]

Since the sockets are for electrical power you would think they'd follow the same color coding standards as required for wire.

IEC Wiring Color Codes for DC – UK  & EU

The IEC DC wiring color codes are adapted  from IEC AC wiring color codes. These rules are applicable in the UK, EU and all other countries who follow the new IEC color codes instead of local and regional codes. The following IEC DC wiring color codes are used for Two-Wire Grounded, Two-Wire ungrounded and Three Wire grounded DC power systems.

Two Wire Ungrounded DC Supply

    BROWN = +Ve (L+)
    GRAY = -Ve (L-)
    GREEN /  YELLOW  = Protective Earth “PE”.

Two Wire Grounded DC Supply

    BROWN = +Ve of a -Ve Grounded Circuit (L+)
    BLUE = -Ve of a -Ve Grounded Circuit (M)
    BLUE = +Ve of a +Ve Grounded Circuit (M)
    GRAY = -Ve of a +Ve Grounded Circuit (L-)
    GREEN /  YELLOW  = Protective Earth “PE”.

Three Wire Grounded DC Supply

    BROWN = +Ve (L+)
    BLUE = Mid-Wire as Center Tapped (N)
    GRAY = -Ve (L-)
    GREEN /  YELLOW  = Protective Earth “PE”.

https://www.electricaltechnology.org/2020/07/electrical-wiring-color-codes-nec-iec.html

[james_s]

Aren't those requirements for wiring in buildings? As far as I know, there is no such requirement for the colors of chassis wiring within equipment. I've even seen stuff where all the wires were the same color.

[David Hess]

I prefer black - negative, red - positive, and green - ground.  But with a floating supply, common is not the same thing as ground, so another color other than green is required, probably leaving white for common which the standard in US electrical wiring where white is neutral.

I have not had my Tektronix PS503A power supplies apart far enough to change their binding posts, but I did buy spare sets of matching binding posts for them.

[tautech]

I prefer black - negative, red - positive, and green - ground.  But with a floating supply, common is not the same thing as ground, so another color other than green is required, probably leaving white for common which the standard in US electrical wiring where white is neutral.

I could say you have just introduced another and conceivably confusing term, common.

What is a common other than a rail we might construct ourselves when connecting a PSU but any decent PSU provides totally isolated outputs none of which are commoned unless we make them such.

However 100% agree that Red, Black and Green for PE are universal color codings for PSU's.
Need to add more well something's wrong with the design IMHO.

[David Hess]

What is a common other than a rail we might construct ourselves when connecting a PSU but any decent PSU provides totally isolated outputs none of which are commoned unless we make them such.

So the Tektronix PS503A, and similar HP power supplies, which provide dual tracking outputs with a common that float, are not decent power supplies?

The ones from HP/Harrison seems awfully popular for not being decent.

[tautech]

What is a common other than a rail we might construct ourselves when connecting a PSU but any decent PSU provides totally isolated outputs none of which are commoned unless we make them such.

So the Tektronix PS503A, and similar HP power supplies, which provide dual tracking outputs with a common that float, are not decent power supplies?

Common implies channels are not isolated as is the case for many modern PSU's.
That matters to some.

[tooki]

Which is completely irrelevant to the question because those standards are for AC, not DC

wont be irrelevant if your bit of pre2004  kit chucks out 2 phases and neutral when your expecting to see a nice plus and negative DC supply

You conveniently stripped off the other half of what I said, which is that those standards are for mains, not test equipment.

The color of mains wiring in the wall has nothing to do with the colors of bench DC test gear.

[tooki]

I prefer black - negative, red - positive, and green - ground.  But with a floating supply, common is not the same thing as ground, so another color other than green is required, probably leaving white for common which the standard in US electrical wiring where white is neutral.

I could say you have just introduced another and conceivably confusing term, common.

What is a common other than a rail we might construct ourselves when connecting a PSU but any decent PSU provides totally isolated outputs none of which are commoned unless we make them such.

However 100% agree that Red, Black and Green for PE are universal color codings for PSU's.
Need to add more well something's wrong with the design IMHO.

He didn't introduce it, it's literally on the front panel of the Tek power supply shown in a photo above.

The fact that most dual supplies today have fully independent, fully-floating channels doesn't mean that the term is made-up, irrelevant, or confusing. It would be if it were used on a fully-floating dual supply. But on ones where the channels are commoned, it makes perfect sense.

I don't think he was suggesting using "common" as the name for ground, though that is what practically every handheld DMM calls its negative input...

[David Hess]

I don't think he was suggesting using "common" as the name for ground, though that is what practically every handheld DMM calls its negative input...

I was suggesting the opposite.  Tektronix marked the floating common between the tracking supplies as black, and the negative output as green.  I would swap those, but not use green for the floating common because green should be chassis ground.  Tektronix used white for the chassis ground, so on this power supply I would swap the green and white.

[rdl]

The web page where I found the info doesn't say that it's only for wiring in buildings. They also mention solar power installations, batteries, boats and vehicles, etc. The reason I quoted the section for UK & EU is because the rest of the world apparently follows the red, black, green convention.

Aren't those requirements for wiring in buildings? As far as I know, there is no such requirement for the colors of chassis wiring within equipment. I've even seen stuff where all the wires were the same color.

[br4n_d0n]

This whole thing stemmed from curiousity, but these last few posts have proven that there really should be some international standard that everyone could follow.

[james_s]

This whole thing stemmed from curiousity, but these last few posts have proven that there really should be some international standard that everyone could follow.

There is a standard that people could follow, there are several standards. I don't really see any particular reason to try to enforce one of them though, the color of the binding posts makes little difference, although in a single voltage DC system I do prefer black and red since that's what the vast majority of things I've worked with uses.

[mwb1100]

https://imgs.xkcd.com/comics/standards.png

[David Hess]

mwb1100 beat me to it.

[Terry Bites]

Rohde = Red, Schwarz= Black. I think the take away messsage here is that Blaupunkt caused the fire in your lab.
By 2030, all terminals will look like a mixture of porridge and raspberry jam. An original HP standard I beleive.
Most manafacturers use logical symbols, formats and standards- a private logic known only to them of course.
Bosch relay numbering insanity persists so it must be a standard, surely?

I'm working on an AI project to decode my new washing machines (obvious) control's.
The washer is wi-fi enabled (yes, WTF?)