Switched receptacles

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Old 09-08-06, 08:30 AM
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Switched receptacles

Hot wire from panel to first receptable,box in living room, Black tied to white to line side of switch loop,, came back on black to receptable, with switch OPEN,, reading 9 volts across receptacle,, replaced switch loop wire thinking there might be a problem with that, dropped voltage to 3 volts,,, Neutral is NOT shared with any other circuit and no other switch loop in this house has this problem,, where the hell am I getting this transient voltage?
 
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Old 09-08-06, 08:36 AM
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Because you are using a digital meter. Put it away. Unless you know how to use it is no good for evaluating electrical circuits.
 
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Old 09-08-06, 12:17 PM
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Ok,, maybe you can explain why its only with this switch loop circuit and not with any others,, and I do believe I know how to use a meter,,
 
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Old 09-08-06, 12:38 PM
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The voltage you are reading is called phantom voltage. Google that term and read all about it. Phantom voltage does not always show up, it depends on the meter used and the exact setup.

You may know HOW to use a digital meter, but you do not know WHEN to use it, or how to read the results.

They are best NOT used when testing an ac circuit as they read phantom voltage, leading to confusion.

If you do inosist on using it, then you should have read the results you see as zero volts. Why? Because you anticipate seeing phantom voltage in this case and you know that the reading you got are phantom voltage and can be ignored.
 
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Old 09-08-06, 04:45 PM
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I did google that and thank you for clearing that up.
Thanks again
BOB
 
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Old 09-11-06, 05:23 AM
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"According to Underwriters Laboratories Inc., this can be a harmless reading and can be caused by the high input impedance of the measuring instrument, which places very little loading on the circuit under test. The capacitance is increased as the length of the run is increased. A 50-foot run may produce a pronounced capacitance effect whereas a one-foot sample may not produce any. This effect has such high impedance that, although a voltage can be detected, there is little or no available current."

If using a digital meter you just have to understand this concept......always ready KNOWN voltage first to achieve 120V nominal and then work from their....understanding that phantom voltage is present but not " ACTUAL" usable voltage for the most part.

Here is an article put out some time ago:

http://www.nema.org/prod/wire/build/upload/Bulletin%2088%202003.doc
 
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