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LEDS barely lit from Neutral only

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    LEDS barely lit from Neutral only

    I remember this thread:
    In which I had a LED vanity barely lit when a loose neutral was on the lighting circuit.

    Well earlier in the week while installing LED troffers I decided to play around and see if I could replicate something similar.
    This circuit lighting circuit consisted of (6) 2x4 controlled by a switch.

    The picture below shows the hot leg completely disconnected but tied through and only the feed neutral and ground connected. And low and behold you see a dim barely lit LED strip.

    I'm not crazy! lol Click image for larger version  Name:	IMG_7890.jpg Views:	0 Size:	86.7 KB ID:	2530575Click image for larger version  Name:	IMG_7889.jpg Views:	0 Size:	46.5 KB ID:	2530576

    190908-2249 EDT


    Measure the voltage between neutral and the switched hot wire with a high impedance, 10 megohm, DVM with switch off. What is this reading?

    Then shunt the meter with an adjustable capacitor box, or resistance box. Adjust until the lights go out. Now what is the voltage reading?

    Make sure no power is applied to the lights. Both the capacitor box, or resistance box must be able to tolerate the stray voltage. In the case of the resistor box do not exceed its power rating.

    Depending upon the results you can start to look for the source of energy. Possibly other kinds of measurements or experiments may be needed.

    Why don't you and others make measurements to try to pinpoint a cause?



      phantom voltage on the neutral? I agree with GAR, when you have weird problems like this the first move is to pull out your volt meter and see what is going on.


        More likely phantom voltage on the disconnected hot run.
        If stray (not phantom) voltage on neutral, there would have to be some return path, such as to EGC because of some filtering or other coupling in the LED driver circuit.


          190918-1714 EDT

          Ran several experiments on a Costco 4 ft twin tube LED shop light.

          First test was an adjustable sine wave voltage from a Variac. One tube dropped out at about 9 V by Variac dial, and the other about 8 V.

          Second test was 124 V to series connection of capacitor box and the LED fixture. Required 0.5 to 0.6 mfd capacitance to maintain one tube on. With 0.1 mfd less flashing of the on tube occurred. Another 0.1 less and neither tube was lighted. Voltage across the fixture was down around 7 V on a Flike 27.

          Stray wiring capacitance in a home or building won't get close to 0.6 mfd.



            Electro-Boom has a you-tube video that shows & explains why some of the LEDs will glow dimly when off. Basically the cheaper ones drivers are not designed well ( no discharge resistor after the bridge rectifier) & a few mico-amps will cause them to glow.

            Skip to about 4:40 in the video that is where he really begins to explain the difference between drivers.
            Advise is a dangerous gift, even from the wise to the wise.