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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: On AC "polarity" posted by Jon Risch on June 16, 2001 at 12:07:47:
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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Follow Ups
- How to check for AC leakage current. - Jon Risch 12:19:44 06/16/01 (0)
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