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

Nsgarch, I am not sure.....

>>"Of course if you decide to use a balanced power unit, all this is of no concern."<<
[Nsgarch]
>>>>>

>>'Maybe, True if all the audio equipment connected by ics is pluged into the same balanced power unit."<<
[jea48]
>>>>>>>>>

After thinking about the balanced 120V (60V-0V-60V) system I am not sure one would not be in the same boat.

It's those darn ICs that connect the audio equipment together.

Two hot 120 volt conductors.
I will call them L1 and L2, 120V.

A power transformer, for say, a power amp.
It is nothing more than an isolation transformer. It has a winding polarity relationship between the primary and secondary windings.

For sake of argument lets label the primary leads H1 and H2. The secondary leads X1 and X2. If the manufacture of the transformer labeled the leads correctly, H1 polarity match is X1 and H2 polarity match is X2.

Connect the audio power transformer primary to the 120V power from the balanced power unit.
(L1 to H1) (L2 to H2). If all the audio equipment power transformers are wired the same the the secondary AC polarities will be the same and so the DC power supplies. (Providing a primary winding polarity to power supply polarity were correct to start with)

What happens if one of the audio equipment power transformer's primary connections is reversed?
(L1 to H2) (L2 to H1)

Any thoughts??

Jea, a 240V line is inherently "balanced". Its ground and neutral are the same (center) conductor, with a potential of +120v on one side and -120V on the other (which reverses every 60 sec. of course.) BTW, I don't believe European 240V power is configured this way (at the outlet), but somebody correct me if this is wrong.

Now to get balanced 120V is a whole 'nuther matter. First you get a great big toroidal transformer and feed it 120V +/_ into one tap and zero volts (neutral) into the other. In a second, identical winding, you take the power out at 60V +/_ tap and 60V -/+ tap and feed one to each blade of the AC plug. To keep the drama queens at U/L happy, you create an artificial ground/neutral for the center ground pin of the plug/receptacle. This is done through some kind of circuitry which U/L is willing to certify provides shock protection ;~)) but it's not an "earth" ground.

If your equipment circuit designer or assembler has been less than attentive as you postulate, then balanced power will save his/her ass because both primary leads are being fed equal (60V) voltage in a "push-pull" arrangement around (or across) an "imaginary" ground (rather than the normal zero volts in one lead and plus-or-minus 120V in the other.) So in the balanced-power-fed component, circuit polarity relative to ground disappears along with any polarity mismatches in the wiring.

>>" a 240V line is inherently "balanced". Its ground and neutral are the same (center) conductor, with a potential of +120v on one side and -120V on the other"<<
>>>>>>>>>>>>>

Correct. The utility transformer's secondary windings are configured as a split phase winding exactly a balanced power system. 120V-0V-120V. The center point of the two connected secondary windings is bonded, connected to earth ground. Just like the 60V-0V-60V system. If all the loads connected to the 120V-0V-120V utility transformer were all 240V loads it would work exactly like the 60V-0V-60V balanced system.

Here is one for you. For a single phase/split phase utility
transformer where 120 volts loads are exactly balanced across the two mains, zerro amperes will travel back on the neutral conductor to the source, the transformer. Example 30 amps of connected 120 volt load from L1 to neutral, and 30 amps of connected 120 volt load from L2 to neutral.
The connected 120V loads from L1 to neutral will be in series with the connected 120V loads from L2 to neutral. Only the unbalanced 120V loads travel back on the neutral conductor to the source, utility transformer.
http://www.ibiblio.org/obp/electricCircuits/AC/AC_10.html#xtocid269100

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?