[Boatanchors] AC plug & receptacle question

[Jim Temple]

Now this is what group support is all about.  Even the newbies can get an
outstanding answer.  We have all been there at some time.  Thanks, Barry

Regards, Jim. 

-----Original Message-----
From: boatanchors-bounces at mailman.qth.net
[mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of Barry H
Sent: Tuesday, February 07, 2006 7:59 AM
To: jfor at quik.com
Cc: boatanchors at mailman.qth.net
Subject: Re: [Boatanchors] AC plug & receptacle question

Some more on this:

The narrower blade on a two-blade plug is hot, the wider one is neutral.
Many appliances are set up this way, even table lamps.

This ensures that it is the hot side that is switched and/or fused, among
other things.  For example, the center contact on a bulb socket should be
hot/switched so that if you go to replace a bulb and the switch is still on,
you might make contact with the outer shell contact, but unlikely to touch
the center one. Of course, it's safer to unplug the thing.

In addition, you don't want a fuse to be on the neutral side.  If it blows,
it leaves the chassis components hot with respect to ground.  That's one
reason why those handy looking old fused plugs are not particularly safe.

When replacing or updating a power cord on a piece of gear, the center pin
goes to (in most cases) the chassis, the black (hot) wire goes to the
switched/fused side and the white (neutral) wire hooks up to the always
connected side.  There are some special situations with AC/DC (hot chassis)
radios, such as those with metal cases, where the ground lead goes to the
case, not the chassis, making sure that the insulating mounts are in place
and still truly insulating the case from the chassis.  If in doubt, ask
about a particular piece of gear on this list or an appropriate one.

Of course, all this assumes that the house wiring is correct.  It's not
uncommon to find an outlet that has been wired backwards, or three-prong
grounded outlets where the ground pin connection is poor or totally
disconnected.  Older homes and buildings were often wired with just two
conductor electrical lines with no ground and the outlets may have been
replaced.  If the old wiring used metal covered "BX" cable, it might be
grounded by means of the clamp to the outlet "Gem" box, etc.  They sell
small tester plugs to check outlets, or you can do it with an AC voltmeter.

Proceed with caution.

Barry









-- "J. Forster" <jfor at quik.com> wrote:
Yong Surk Lee wrote:

>  US uses 117volt AC household current.
> Most AC plugs have two pins, one wide and the other narrow.
> Also AC receptacles have two holes the same way.
> So the plug always fits one way.
> Why is this necessary?

So you don't interchange the Line and Neutral wires.

> Some of the US AC plug has the third pin which I believe is ground.

The round or 'D' shaped pin is Ground

> I have a US made AC cord that have 3 pins and 3 wires connected to it, 
> white, black and green. I know the green is ground. The white and 
> black wires are interchangeable?
> de HL1FB/WW6N

NO !!!  The White is the Neutral and in an unbalanced 115 V US system is
near Ground.
The Black is the Line or Hot (Black = DEATH !!) It is 115 V above ground.
(in a 230 V balanced the hots are Black and Red)

-John

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