[Boatanchors] BA's and 3-wire cords

[WA5CAB at cs.com]

In a message dated 1/11/2005 9:31:09 PM Central Standard Time, W4AWM at aol.com 
writes: 
> The way I see it, if a 3 wire cord set is installed on an AC/DC set in the 
> proper manner, there should be no problem.  Please explain it to me if there 
> is.
> 

There is no proper way to install a three wire cord in a metal chassis 
traditional AC/DC set (unless you install an isolation transformer).  AC/DC sets 
have one side of the AC line connected to the metal chassis.  Depending upon how 
you turn a two wire plug and how your outlets are wired, this could be the 
neutral or the hot.  If you replace the 2-wire line cord with a three wire one, 
and tie the ground and one side of the line to the chassis, what happens when 
you plug it into an outlet depends.  If you connect the white wire to the 
chassis , the white wire goes to the proper pin in the three wire plug and your 
outlets are wired to code, everything's more or less fine (except legally).  If 
not or if not or if not, you'll get arcs, sparks and either a blown breaker or 
a fire.  

> Here in Virginia, the neutral and the ground buss are both at ground 
> potential and in fact, are connected to eachother in the main breaker box.
> 

No and maybe/maybe not.  The neutral and ground wire are tied together either 
at the nearest pole or at the nearest transformer.  Whether they are tied 
together in the main fuse/breaker box depends upon local code.  Go to a store 
selling decent quality main breaker boxes, open some of them up and read what it 
says on the little white paper tag under the green screw.  Furthermore, the 
neutral is a current carrying conductor and is not at ground potential anywhere 
away from the nearest ground rod.  Even in my own house and shack, where much 
of the wiring was run by me over the years, I always treat the white wire no 
differently from the black until proved otherwise.

I would not personally replace the two wire cord on any AC/DC set with a 
three wire one (unless I also installed the aforementioned isolation transformer). 
 I would make sure (and replace if necessary) that the plug is polarized, and 
make sure that all of the outlets in my house and shack are (a) polarized and 
(b) wired properly.  If someone gets electrocuted while working on an AC/DC 
set with a two wire cord, that's simply Darwin at work.  However, if I put a 
three wire cord on it, I may be half at fault, even though the recently deceased 
should have known that it shouldn't have had a three wire cord on it in the 
first place.  There is no current US electrical code that allows tying the 
neutral and ground together downstream of a breaker panel.  Some codes allow 
grounding the neutral in sub-panels and some don't.  But definitely not in portable 
equipment.  That's simply death waiting for some poor fool to come along.

Robert Downs - Houston
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