AC cord polarity?? Does it matter???????

Mitchb:

I don't know why your power cords would be reversed, but to meet current NEC codes, they have to be polarized the the right way. For your basic 115 V three prong cable, the big one is earth, the wide one is neutral, and the smallest one is the hot or line.

Now that being said, there are some older cords which are not polarized correctly, as they were made long before polarity for line cords was written into the NEC. The thing is, I am pretty sure by the time the IEC connector came along, polarity had been in the code for a while. I do believe this was the reason the IEC connector was adopted. I am writing this from memory; I don't have a history of NEC at my disposal.

I suggest you pitch the incorrect polarity power cords. If you are in doubt about which one is correct, go to your local hardware store and buy a Belden cord for about 7 bucks or so. This will be correct; compare everything to this and toss the ones which are polarized opposite.

You can check your wall outlets in your house/apt easily enough: when you are the hardware store, pick up a line polarity tester for around 5 dollars or so. On this are a series of LEDs which light up depending on what is wrong. You can get expensive and blow up to 10 bucks on one if you want to also check the GFI outlets in your kitchen or bathroom, but you won't need GFI testing for your stereo stuff.

By the way, if one of the cables you find is polarized backwards and it has a UL sticker on it, please call your local UL office, they are in the phone book. I am SURE they will be MOST interested!

Am I missing something?

Typically, AC is fed into a components isolation transformer, through full rectification and large filter/storage capacitor networks accross the secondary outputs, thus producing DC voltage. This, intern, feeds all the DC circuits typically isolated from their metal chassis (circuit depedant). Why does it matter which AC polarity feeds the transformer? Isn't DC is the final product?

In Jeff's artical, "all transformers will leak a little current to the component's chassis". Shouldn't it be "leak inductance" or "capacitance"? With lots of chassis made from aluminum, where's the stray field interaction with sensitive circuits, etc.? Most audio components isolate their audio I/O connectors from the chassis, thus minimizing ground loop potential between components with grounded chassis. Any minute stray voltages that do develope along steel chassis, doesn't default into audible subjectiveness.

Any helpfull explanations?

Metro04, you are correct in your basic evaluation of the situation, but yes, you are missing something, and that's the damn power company!

As the article Jea48 mentioned above illustrates, the power company uses (literally) the ground for its return leg to the generator. Which means in normal 120V house systems, the neutral blade is not always at zero potential relative to ground (in fact I've never found it to be so.)

So it's not the component's fault exactly, but depending how a components (power supply) circuits happen to be oriented to this "ground leak" current will mean slightly more or less noise (usually 60 cycle hum) in your system.

Balanced power units simply eliminate this problem altogether.

Hsgarch,

Thanks for getting back with me.

Even if the neutral wasn't at zero potential, most domestic voltges provide more than adequate supply for most component DC rails and regulated circuits (+/- 0.5 to 1.0 VAC of the localized incoming supply, which can swing pretty widely throughout the day, and per region).

In most homes, aren't the neutral and "ground" combined within the breaker box? This SHOULD place the N and G at the same potential, thus supplying the proper circuit voltage into the component's isolation x-former.

Now, what happens to so called "leakage inductance" within a non-ferrous chassis (aluminum)? What about components utilizing un-grounded chassis (2-prong cords), or a combination of the two? If none of the component's circuits are electrically grounded to the chassis, what are these stray voltages going to affect? In a ferrous chassis, I can see some 60 Hz magnet issues affecting certain circuits, but not with aluminum. Any minute x-former leakage would stay localized around itself. Right, or what?

I'm just concerned about blanket statements towards these wiring orientation claims, and whether they are indeed audible in most scenarios.

Your responces are always welcome, and I'm not trying to be argumentative. I do have lots of electronic background, but claim to know everything.