AC cord polarity?? Does it matter???????
>>"I've just noticed that from experimenting with preterminated factory builty cords that not all companies use the same polarities. Even with two stock cords, one from USA made in China and one from China made in China for USA the polarity of the cords are reversed."<< >>>>>>> Just one of the problems with after market power cables. Very few if any are UL listed. http://www.marchansen.com/tn102/ Reversed AC polarity can cause noise and hum from your audio system as well as effecting it's sonics. http://forum.audiogon.com/cgi-bin/fr.pl?htech&1014011751&openmine&zz |
Yes. Depending on the resolving level of your system the individual components of your system will have different sonics depending on the orientation of the ac plugs. Experiment with each component to determine which orientation sounds best to you and mark the plug for future reference. When manufacturers make a component little consideration if any is given to plug polarity. It is of low priority to them. |
| Post removed |
Van Den Hul make a Polarity Checker. A small pen shaped digital meter. You can also check all your components and plugs for correct polarity with a simple test meter. Instructions from the Chesky website: By Michael Trei One simple tweak that many people tend to ignore, is to be sure that each piece of gear is plugged into the power outlet using the proper polarity. The power supply transformer in every piece of gear will leak a little current to the component's chassis, and in most cases, you'll get better sound if this leakage is minimized by observing the proper A/C plug orientation. A few decades ago, audio gear had simple two prong A/C plugs that could be inserted in the socket either way, but now all plugs are polarized so that they only go in one way. To get around this, we need to use a simple adapter called a cheater plug, available for a buck or so at any hardware store. The cheater has two narrow prongs that allow you to use it in the socket either way, and cheaters will also take a three prong plug with a ground pin, replacing the ground prong with a metal tab or wire that you can connect to the center screw on the outlet plate. If you want to reverse a three prong plug, you'll want the version that uses a wire so that you can still connect the ground with the plug in the reversed position. While there are fancy polarity checkers that you can buy from companies like Van den Hul, the same tests can be done using a simple inexpensive digital voltmeter. First, disconnect all of the cables except the power cord from the component that you want to check, as any connection to other gear can throw off the results by providing multiple grounds. Then plug in the component using the normal orientation, but with the cheater plug in place. If the component uses a grounded cord, make sure to connect the green ground wire on the cheater plug to the outlet plate screw. Turn the component on, and set the voltmeter to A/C volts. I usually simply pinch one probe between the fingers of my left hand, then I hold the other probe in my right hand and touch the tip to a metal part of the component's casework such as a cover screw. Note the reading in volts. Turn off the component, reverse the plug in the wall outlet, turn the component on again and check the voltage once more at the same point on the case. If you got a lower reading this way, leave the component plugged in as it is, otherwise remove the cheater and plug it in normally. If you repeat this test for each component, you should hear cleaner, more transparent high frequencies, and a lower overall noise floor. Total outlay? About five bucks. OK, $25 if you need to buy the multimeter, but still a bargain. . . . |
| Post removed |
>>"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. ========== Nsgarch, What is your thoughts of feeding a balanced power unit from 120V? Jmho, I believe there would be better isolation if a balanced power unit was feed by 240 volt. Here is some reading material. Make note of how the utility companies bond the high voltage neutral and all the secondary neutrals together at every utility transformer. This can't be good for AC noise.... http://www.mikeholt.com/documents/strayvoltage/pdf/DangersofStrayVoltageandCurrent.pdf Jmo it appears to me the only way to get total AC isolation is with an isolation transformer fed from 240 volt. Jim |
| Post removed |
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. |
| Post removed |
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. |
| Post removed |
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. |
Metro, the answer to: "In most homes, aren't the neutral and "ground" combined within the breaker box?" Is no. And this is very important to understanding the "leakage" problem oulined in the article you cite above. The neutral is zero relative to the 120V on each side of it. But it is not zero relative to earth ground. So depending how the power supply in a component is laid out, connecting one of the two AC plug blades to neutral will result in less ground current leakage through the "neutral" leg of the power supply circuit. As a matter of fact, that is why, as someone described above how to measure for the best plug orientation, they specifically mentioned not to connect the ground pin of the AC plug when doing the measurement. To which I'll add two more rules: turn off the component, and disconnect all other connections to the component (ICs, spkr cables, coax cable or digital feeds, etc) because they may be connected to ground somewhere on their other ends, and you don't want that. The idea behind this testing procedure is to "force" current that would,in grounded components, ordinarily drain to ground, instead to "leak" through the neutral so it can be measured. And then minimized by choosing the proper plug orientation. So why is doing this a good thing? Because when everything is hooked back up, some current will drain to ground through the ground leg, and every one of these conditions in your system represents a ground loop which increases the baseline level of hum (and sometimes noise) in the system. |
| Post removed |
Nsgarch, Thank you for the informative response, and will look into it further. I did find some interesting articles after posting my last response, but still have inquiries pertaining to non-ferrous chassis having the same effect. Lots of veteran electronic engineers at my work, so I'll get to the bottom of this, yet. Thanks again... |
First, there is no such thing as "zero volts," we just agree to call something zero (the earth) and measure everything relative to it. It is completely arbitrary. Second, neutral and ground are bonded in the sevice panel and only there. Go to Home Depot and look at a panel. The neutral bar and the ground are bonded. Another term for neutral is grounded conductor. Third, in a house, circuits are taken off each "hot" conductor, and the currents in the grounded conductors (which are all tied together) cancel each other out. In other words, if, by chance, the currents on each hot leg were exactly equal, the grounded conductor could be disconected from the service neutral (and the ground) and every thing would work. All the current would flow through the hot legs. Fourth, the reason the grounded conductor measures hot relative to ground is because the conductor has resistance, and there is current flowing through it. Since there should be no current flowing in the ground, and the two are tied only at the panel, there will be a voltage difference at the outlet (but not at the panel). Fifth, Mr. Holt does not mention, although I am sure he knows, that all power is generated and transmitted as three phase, each 120 degrees apart in time. When each phase has equal current, they sum to zero and there is no net current to flow through the ground. Any current is due to the three phases being unequal and will be small relative to the total current draw. If any significant power is disipated in the Earth, the power company loses money. The Earth naturally has absolutely enormous currents flowing in it, making the Earth into a giant magnet. Polarity is a safety issue. |
>>"Fifth, Mr. Holt does not mention, although I am sure he knows, that all power is generated and transmitted as three phase, each 120 degrees apart in time. When each phase has equal current, they sum to zero and there is no net current to flow through the ground. Any current is due to the three phases being unequal and will be small relative to the total current draw. If any significant power is disipated in the Earth, the power company loses money."<< >>> >>"Mr. Holt does not mention"<< >>>>>>>>> The article was not written by Mr. Holt. ===== >>"When each phase has equal current, they sum to zero and there is no net current to flow through the ground."<< >>>> In my neighborhood there is only one 7200V HV line on top of the power pole, feeding many pole mounted transformers. Lets say for argument, (A) phase of the 3PH 4W 7200/13200V wye feeder leaving the substation. No balance here....Just one ungrounded 7200V conductor and the grounded conductor, the neutral (single phase).... No balance in the (B) phase neighborhood or even the (C) phase neighborhood. I will grant you at the point where the 3PH 4W HV feeder branched out going their separate ways, from that point where the neutrals were joined to the main feeder neutral, back to the subtation the HV neutral only carries back the unbalanced load plus*.... ======= * http://www.ibiblio.org/obp/electricCircuits/AC/AC_10.html#xtocid269101 |
Jea48, thanks for straightening me out. The author is Donald Zipse, and Mr. Holt reproduces the article. I should have been more careful. I agree with your point about each neighborhood being on a different phase, but my point is that the net return current of the entire system is very small compared to the load. While each neighborhood may be on its own phase, my third point still holds and the neutral current is relatively small. Mr. Zipse's proposal (comparing fig. 21 and 22) is to remove the neutral-ground bond from the panel and replace it with a dedicated ground wire back to the transformer neutral-ground connection. One problem I can see with this approach is that if this new 4th ground conductor was damaged or the transformer ground missing or damaged, as far as the customer could tell, the system would function normally. It much easier to visually verify the neutral-ground bond at the panel than to vouch for the integrity of a 4th conductor to an off site ground. I can appreciate the logical appeal of completely separating the neutral and the ground functions and wires. However the cost to implement would be huge, the benefit theoretical. The author himself states that his proposal was "soundly rejected" by both the NESC and the NFPA. |
| Post removed |
