line cord color code - safety

Fred Olsen fwolsen at EXECPC.COM
Fri Aug 9 20:45:24 EDT 2002

JR LINDEN wrote:

> I've got a Drake AC-4 power supply with the ac plug cut off.  Could someone
> tell me the proper hookup for the blue and brown wires?  The green is ground
> but does it matter which of the other two is hot or line.

It sure does, JR.  As always, this is a major safety issue, on which
many of you know I've ranted before.  ;<)  Gary K4FMX is correct in
saying that the high side needs to go to the fuseholder, but that
requires some expansion.  First, your short answer.
Brown=Black=High.  Blue=White=Low.  Think of blue as a 'cool' color.
Green and green/yellow are absolutely reserved for the "equipment
groundING" conductor and must NEVER be used for anything else.
The brown-blue-green (or green/yellow) is the IEC international standard
color code.  Note that these colors are normally used on 240V, with two
'high' conductors, so blue being 'low' only applies in North America,
and only on 120V.

Instructions, a P/L, and a skiz for the AC-4 is on BAMA, and my answer
was derived from that.  Thanks, Ken.

The AC-4 is 120/240V.  If you're running it on 120 the 'high' needs to
go to the fuseholder.  I don't know what style fuseholder the AC-4 has
but if it has an "extractor post" type, i.e.: one where the fuse is
extracted from the body by a screw-in or bayonet cap, then:
NOTE: The line (mains) input MUST be wired to the TIP contact of the
fuseholder.  The chassis load must be taken from the ring contact.  This
reduces the possibility of line contact when extracting the fuse.  Much
older and some newer gear is miswired in this regard and should be
changed.  It was often thus as a production convenience.  No excuse.
So run the black or brown wire to the tip of the fuseholder.
The white or blue wire is the low/"neutral"/groundED conductor.
And green or green/yellow is of course the ground/earth/groundING conductor.

240V operation is a different kettle of fish, and must be handled with
caution on many units due to design compromises.  First, the AC-4 and
many other units have only one fuseholder.  Since with 240V one has two
'high' wires one should also have two fuses.  No such luck.  Be aware
that the fuse on one 'high' can blow and still leave 120V to ground
roaming around the chassis.
NOTE: And also leaves 120V in the unit under operation in the case of
the AC-4 and many other remote supplies.  Beware of the switch loop
through the end unit!  (Internal blue and brown, pins 1 and 2, on the AC-4.)
This also applies to any European gear which DOES have two fuses, when
only one has fused.  The only easy way around that problem would be a
two-pole common-trip circuit breaker, but that's beyond this discussion.
  Obviously then one also needs two-pole switching, which the Drake and
a lot of other gear does not have.  Which you CAN'T use when running on
120V.  Catch-22.

If one runs the AC-4, or a linear or whatever, on 240V it's common
practice to use the 120V black/white/green line cord with a 240V plug.
Strictly speaking that's an electrical code violation, as white is
reserved for the groundED conductor unless it has been taped over with a
different color, e.g.: red.  At both ends.  You'll never win that battle
because almost no manufacturer provides a black/red/green line cord for
240V operation.  The IEC colors are actually suitable for 240V in North
America, but you need to think twice and keep things straight.

One other point, then I'll shut up.  It's preferred practice to connect
the 'low' of a 120V line to those ends in common of the transformer
primaries which are the "start" ends of the windings.  Any given
transformer may or may not use standard color coding for its leads, so
it can't always be determined.  If the schematic shows a dot marking one
end of the winding(s) then that is the start end.  If it can be visually
determined that one end of a primary is OBVIOUSLY "inboard", toward the
core, then that is USUALLY the start.
One purpose of this is to reduce voltage gradient stresses across the
transformer, which can have an effect on long-term life.

Anyone is welcome to expand, explain, or show how dumb I am.

Good luck, be safe,
Outgoing checked by Norton AV.

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