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In Reply to: The best way to reverse ac polarity posted by jcb3 on June 13, 2001 at 13:27:26:
There are safety issues, and then there are audiophile concerns about leakage current, and interchassis potentials.First, see:
http://www.soundstage.com/articles/pete01.htmThen:
http://www.audioreview.com/message/cgi-bin/dcforum/dcboard.cgi?az=show_thread&om=438&forum=DCForumID3&omm=2The latter refers to equipment that does not have a polarized plug. Most equipment today does have such a plug, and hopefully, between UL and the manufacturer, they have gotten it right. However, I have seen equipment incorrectly wired, either via a mistake in assembly OR via incorrect design and either no UL or the UL guy was asleep at the wheel. So in essence, one might be forced to correct an incorrectly wired piece of gear.
The whole purpose of minimizing leakage currents for each piece of equipment, is to minimize interchassis potentials, and hence, reduce the need for a heavy ground connect between each piece of equipment in the system. The theory is that if interchassis potentials were reduced or eliminated, that many of the sonic difference between interconnects would dissappear or be greatly reduced.
It is possible that minimizing leakage currents would cause the component to need to be wired such that it does violate safety aspects, and in these cases, a competent technician would have to correct the caps that were incorrectly placed in relation to the line and the chassis.
I would not recommend reversing a polarized 2 wire plug without complete and due consideration of all safety factors, it is not to be done by those who are not capable of analyzing the AC wiring and filter caps involved.
Certainly, one should never reverse the hot and neutral in the wall outlets!
Sometimes even equipment with three prong plugs have the hot and neutral reversed, and the consequent huge increase in leakage currents. Again, these should be 'corrected' only by competent and knowlegable individuals, and not changed willy-nilly by laymen who are not up to speed on such things.
Jon Risch
Follow Ups:
First: ALWAYS BE CAREFUL WHEN WORKING WITH AC LINE VOLTAGES !!!!KEEP ONE HAND IN YOUR POCKET, AND BE AWARE OF WHAT YOU ARE DOING AT ALL TIMES !!!! USE AN INSULATED CLIP LEAD TO CONNECT THE OTHER METER LEAD TO THE RCA SHELL/GROUND TO ALLOW THE USE OF ONLY ONE HAND.
The method to check for AC leakage current is as follows:
First use an ANALOG AC voltmeter (even a $12 one from RS will do). Set to AC volts, 200 VAC range (enough to cover up to 120V)
Then, dissconnecting the interconnects, so that the component is only hooked up to the AC line, test for a reading between the AC wall outlet ground pin (the third or U shaped outlet hole) and the components input jack grounds, the outer shell of the RCA jack.
Note the reading, and then reverse the plug (this is for 2 prong gear WITHOUT a polarized plug!) and note the reading again. Usually one will be lower than the other. If there is no meter indication high enough to reliably read either way, then try switching the meter TEMPORARILY to a lower more sensitive range. Again, one plug orientation should be lower in reading than the other. Use this orientation. I mark the plug with a red dot on the side that goes into the small blade outlet hole (hot), just for future reference.
Some units will show almost the full 120 volts when making this measurement (this can indicate a problem), others will show around 60 volts, and most will be in the several volts to dozens of volts range.
Repeat for each component in the system, and use the plug orientation that gives the lowest voltage reading.
Once all the components have been properly oriented, then re-connect all the interconnects, and cautiously turn up the volume to check and see that there are no problems.
Use of an analog meter in voltage mode will effectively be measuring leakage current, and the lowest reading provides the lowest leakage current for that component. Digital meters do not work on current directly like an analog meter movement, you are taking advantage of the fact that an analog meter is current operated to make these measurements.
DO NOT PUT THE METER IN AC CURRENT MODE, OR TRY TO USE A DIGITAL METER IN AC CURRENT MODE ! This is potentially dangerous, and at the least, might burn up the meter.For audio gear with polarized 2 prong plugs, or for 3 prong connected audio components, if you wish to temporarily use a cheater plug to check the AC leakage current while all the components are disconnected, then DO NOT touch the component case or chassis during the measurement, and as soon as the measurement is over, disconnect the equipment and remove the cheater plug!
If the leakage current is lower with the hot and neutral reversed, DO NOT automatically just use a cheater plug on this or other components in the system, see:
http://www.AudioAsylum.com/audio/tweaks/messages/36908.html
and seek professional help to solve the problem, or contact the manufacturer.Jon Risch
NOTE: THE AUTHOR SHALL NOT BE HELD RESPONSIBLE IN ANY WAY FOR THE USE OF THE INFORMATIONAL CONTENT OF THIS ARTICLE, OR DAMAGES OR INJURIES ARISING FROM THE USE OF SAID CONTENT. THE AUTHOR URGES ALL POSSIBLE SAFETY PRACTICES. CONSULT YOUR LOCAL LIBRARY FOR INFORMATION ON AC LINE SAFETY PRACTICES, AND GOOD ELECTRICAL MEASUREMENT TECHNIQUE. IF YOU CAN NOT FIGURE OUT THESE THINGS FOR CERTAIN, CONSULT OR HIRE A LOCAL ELECTRICIAN TO DO THEM FOR YOU.
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