[Boatanchors] AC plug & receptacle question

[Barry H]

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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