Color codes for DEC power supply terminals?

tony duell ard at
Sun Apr 12 00:16:29 CDT 2015

> I'm trying to determine if DEC used any standards when choosing colors
> for the terminal connections on their power supply systems.  I have a
> non DEC 'DECTape' drive I'm in the process of bringing back from the
> dead and am troubled by the manufacturers use of colors on their
> terminals.  Some make sense: 'black', 'white', 'green' for primary
> color, although there is a block of 'red' used as an alternate
> connection to the 'black' (USA: 'hot' leg) of the primary (115VAC)
> connection.

Red was used for mains live (hot, line, phase) in England until the 1970s,
I remember the change to the brown/blue/green&yellow we have now
in flexible cables, and in internal equipment wiring long after that. 
Confusingly (for you) [1] black was used for neutral (your white).

[1] Not as confusing as the change to fixed wiring, e.g. in buildings. Until
about 10 years ago in the UK, the 3 phases (live) were red,yellow,blue with
a black neutral. Now they are brown,grey,black with a blue neutral. Which
means if you see a distribtion board fed with a black and a blue wire it 
could be either way round depending on when the wiring was installed. 
Needless to say the only thing to do is what you'd do anyway, check it.

> Others include 'blue', 'yellow' and 'orange'.
> I'm familiar with DEC's use of 'red' for +5, and 'orange' for +15 (or
> perhaps it was +12) but these do not seem to be the choices here.

Blue was commonly used for -15V by DEC.

I think the printsets of DEC backplanes (and things like the 11/45, 11/34 CPU)
give some of the colours on the diagrams.

> Any ideas?  Perhaps the manufacturer just pulled some out of their hat.


AFAIK, there are regulations that specify the colours to be used in the mains 
cable, and nobody would be stupid enough not to follow them. But for the 
internal power wiring of a device, or the special cable between a PSU and
its device, all bets are off.


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