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#23378 - 03/16/03 07:25 PM History of color coding?  
rmiell  Offline
Joined: Nov 2000
Posts: 242
La Junta, Co. USA
Anyone have any history about when and why the present use of black for hot and white for neutral(grounded) for AC, while red is used for positive and black for negative in DC, came into being?

Did Edison or Tesla ever get into this?


Rick Miell

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#23379 - 03/17/03 12:21 AM Re: History of color coding?  
DBC1  Offline
Joined: Mar 2003
Posts: 16
Tulsa, OK USA
Rick, sorry cannot help with when black and white were used for AC circuits.

But you are mistaken about your DC colors. There is no color code for DC. Each industry does there own thing. Walk into any telephone office and it will vary from office to office. The positive is black because it is the grounded conductor, just the oppisite of ac. The negative, or hot, can be black, white, blue, or red. It's just to confuse the Russian's. [Linked Image]

#23380 - 03/17/03 09:25 AM Re: History of color coding?  
electure  Offline

Joined: Dec 2000
Posts: 4,259
Fullerton, CA USA
My earliest reference book, 1924, makes no mention of any colors for AC or DC.
It does refer to "neutral", but doesn't say anything about grounding it. The only mention of grounding is that NM Cable contained a wire 2 sizes smaller than the others, which should be used for grounding of metal boxes...S

#23381 - 03/17/03 07:47 PM Re: History of color coding?  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
You may have already seen this, but we had quite a discussion on the color codes, past and present, of various countries. The thread is here with a condensed summary posted in the technical reference section here .

These just go to show that what might seem to be an "obvious" choice of colors to somebody who grew up with them, might not be to somebody else.

In the West we accept red and black as common colors for positive and negative on D.C., such as on test leads, but I have a Russian-made meter which has white and black leads and probes (I still have no idea which way round the Russians use them.)

On the D.C. issue, here in England black was adopted for the grounded pole of a D.C. system (as it is with A.C. systems). Red and blue were then used for D.C. lines positive or negative with respect to ground on a 3-wire system, but our "code" for building wiring specified that the hot pole of a 2-wire DC circuit should be red, even where it waa derived from the negative side of a 3w DC system!

You can see the red/blue coding on D.C. switchgear on the London Underground (subway system) and elsewhere. For example, in old G.P.O. telephone offices the positive (grounded) busbar was bare while the negative busbar was identified blue.

I too would be interested to learn when the common American colors came into general use, and/or when they were first specified by the NEC.

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