ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
Fujifilm Recalls Power Adapter Wall Plugs
by Admin. 01/16/18 07:04 PM
VDE 0100 to introduce AFCIs
by sparky. 01/16/18 06:36 PM
Air Compressor feeder conductor sizing
by Potseal. 01/15/18 09:08 PM
Under carpet cable?
by HotLine1. 01/15/18 09:57 AM
New in the Gallery:
Housebilding DIY wiring
SE cable question
Who's Online Now
0 registered members (), 7 guests, and 8 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
History of color coding? #23378
03/16/03 06:25 PM
03/16/03 06:25 PM
rmiell  Offline OP
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

Work Gear for Electricians and the Trades
Re: History of color coding? #23379
03/16/03 11:21 PM
03/16/03 11:21 PM
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]

Re: History of color coding? #23380
03/17/03 08:25 AM
03/17/03 08:25 AM
electure  Offline

Joined: Dec 2000
Posts: 4,263
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

Re: History of color coding? #23381
03/17/03 06:47 PM
03/17/03 06:47 PM
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.


2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman


Member Spotlight
Fullerton, CA USA
Posts: 4,263
Joined: December 2000
Show All Member Profiles 
Top Posters(30 Days)
sparky 23
Admin 20
Potseal 13
Popular Topics(Views)
243,516 Are you busy
180,314 Re: Forum
170,811 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.015s Queries: 14 (0.003s) Memory: 0.9595 MB (Peak: 1.0904 MB) Zlib enabled. Server Time: 2018-01-17 13:15:56 UTC