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Author Topic: Interesting outlet at show last night  (Read 6914 times)

John Roberts {JR}

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Re: Interesting outlet at show last night
« Reply #20 on: March 22, 2016, 10:35:53 am »

I can't express the math and physics to back up my assertions. But here's another mystery to consider:

In my family room, I have a ceiling fan with a light kit and night light function. The fan motor and the lights are controlled by separate wall switches, in addition to the pull-chains on the unit itself. I have installed four C7 LED bulbs in the sockets for the night light.

If I pull the chains so the night light function is "on" -- the position of the pull chain for the speed of the fan motor seems irrelevant -- and have both wall switches off, the night lights glow very dimly. If I turn on the wall switch for the fan, (again, the fan pull chain doesn't make a difference) the night lights glow slightly brighter (but not full brightness).

In summary, with supposedly no power going to the fan/light unit, the LED night lights still glow. Hmmm.
A perhaps simpler explanation, if line and neutral are reversed, such that the light switch is breaking the neutral side instead of breaking the hot, line side. When switched off the lamp is energized and swinging 120VAC just with a floating return. Any capacitance on the return side may draw enough current to explain the glow coming from very efficient LED lamps.  I have heard similar reports about CFL lamps that glow briefly after being turned off.

Caveat, this is just speculation but logical to me.

JR

 
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Corey Scogin

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Re: Interesting outlet at show last night
« Reply #21 on: March 22, 2016, 10:52:17 am »

My favorite DMM for production - $150, does high and low impedance AC voltage measurements, has built-in NCVT:
http://en-us.fluke.com/products/digital-multimeters/fluke-117-digital-multimeter.html

(off topic)

Here's the tag line for the Fluke 117:

The Fluke 117 digital multimeter is accurate even in low light. Check out the best non-contact multimeter for efficiency in demanding settings today!


This struck me as a strange/funny description. Especially the first sentence. Are they saying that many meters are not accurate in low light? Does this meter allow me to measure things without contacting them? 
I know what they're trying to say but they're not saying it well.
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Jonathan Johnson

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Re: Interesting outlet at show last night
« Reply #22 on: March 22, 2016, 11:03:05 am »

In summary, with supposedly no power going to the fan/light unit, the LED night lights still glow. Hmmm.

I think the simple answer lies in the switch loop. There is an unswitched hot running in parallel to the switched feeds to the light and fan. When the switches are open, the hot capacitively couples to the switched feeds. When turning on the fan switch, now there are two hots capacitively coupling to the light feed. The voltage induced by the coupling is enough to light the LEDs; the impedance of the LEDs is high enough to not draw the voltage down to zero.

Basically, the LED lamps in conjunction with the switch wiring are acting as a NCVT.
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John Roberts {JR}

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Re: Interesting outlet at show last night
« Reply #23 on: March 22, 2016, 11:49:52 am »

I think the simple answer lies in the switch loop. There is an unswitched hot running in parallel to the switched feeds to the light and fan. When the switches are open, the hot capacitively couples to the switched feeds. When turning on the fan switch, now there are two hots capacitively coupling to the light feed. The voltage induced by the coupling is enough to light the LEDs; the impedance of the LEDs is high enough to not draw the voltage down to zero.

Basically, the LED lamps in conjunction with the switch wiring are acting as a NCVT.

That is logical too, I have heard reports of glowing CFL/LED lamps in circuits that didn't have an extra live wire in the bundle.

One obvious difference between a NCVT and your situation is the parallel wire run, tens (?) of feet long could have significant coupling. 

JR
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Stephen Swaffer

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Re: Interesting outlet at show last night
« Reply #24 on: March 22, 2016, 03:01:51 pm »

I can't express the math and physics to back up my assertions. But here's another mystery to consider:

In my family room, I have a ceiling fan with a light kit and night light function. The fan motor and the lights are controlled by separate wall switches, in addition to the pull-chains on the unit itself. I have installed four C7 LED bulbs in the sockets for the night light.

If I pull the chains so the night light function is "on" -- the position of the pull chain for the speed of the fan motor seems irrelevant -- and have both wall switches off, the night lights glow very dimly. If I turn on the wall switch for the fan, (again, the fan pull chain doesn't make a difference) the night lights glow slightly brighter (but not full brightness).

In summary, with supposedly no power going to the fan/light unit, the LED night lights still glow. Hmmm.

Is it safe to assume that you are being precise is using the term switches?  The lights are not controlled by a dimmer, correct?
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Steve Swaffer

Jonathan Johnson

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Re: Interesting outlet at show last night
« Reply #25 on: March 22, 2016, 06:08:34 pm »

Is it safe to assume that you are being precise is using the term switches?  The lights are not controlled by a dimmer, correct?

Correct. No dimmer in the circuit. (In fact, now that I think of it, there are no dimmers anywhere in my house. I haven't needed one and the wife hasn't asked for one, so maybe I'd better keep my mouth shut.  ;) )
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Kevin Graf

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Re: Interesting outlet at show last night
« Reply #26 on: March 26, 2016, 08:33:25 am »

Some older switches have a neon bulb. That might be enough leakage for an LED or sensitive meter.

Some nit-picking electricians say that a switch w/neon changes a switch wall-box to an outlet box.
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Matt Greiner

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Re: Interesting outlet at show last night
« Reply #27 on: September 22, 2018, 12:16:34 pm »

I generally take along a SureTest Analyzer which tests EVERYTHING at once including voltage, frequency, voltage drop at 15 and 20amp loads, ground impedance, etc...  However, it still can't find an RPBG, so I always use a NCVT to check for a hot ground. http://www.idealindustries.ca/products/test_measurement/circuit_analyzers/suretest_circuit_analyzers.php

At $300 a SureTest Analyzer is pretty expensive for casual testing, but maybe worth it for touring where you don't want to plug a $100,000 console into an unknown receptacle. Even if you bring along your own distro, you never really know what it's plugged into unless you meter it first. 

Now that I think about it, I've never plugged a SureTest Analyzer into an outlet miswired with 240-volts, so I'm going to talk to their engineers to see if it will survive that kind of over-voltage before I blow up a $300 tester.

Sorry to wake this zombie thread, but I wanted to add some info that I found when doing some research and looked at the link Mike provided.  According to the Ideal site for the SureTest, the AC Voltage Range is 85.0 - 265.00 VAC.  So it appears that it will be fine if you happen to use it on an outlet that is miswired.  I can think of one time when I plugged my distro, which had a 50 amp range plug on it (NEMA 14-50) into a receptacle that was wired 3 phase.  This would have been extremely handy to have.   >:(
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John Roberts {JR}

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Re: Interesting outlet at show last night
« Reply #28 on: September 22, 2018, 12:58:13 pm »

Sorry to wake this zombie thread, but I wanted to add some info that I found when doing some research and looked at the link Mike provided.  According to the Ideal site for the SureTest, the AC Voltage Range is 85.0 - 265.00 VAC.  So it appears that it will be fine if you happen to use it on an outlet that is miswired.  I can think of one time when I plugged my distro, which had a 50 amp range plug on it (NEMA 14-50) into a receptacle that was wired 3 phase.  This would have been extremely handy to have.   >:(
Back when I was still optimistically pursuing my outlet tester I bench tested a neon lamp driven from a resistive voltage divider that would illuminate for 240V but remain dark for 120V.

A decent VOM can confirm AC voltage pretty competently.

JR
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Matt Greiner

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Re: Interesting outlet at show last night
« Reply #29 on: September 22, 2018, 02:43:53 pm »

Back when I was still optimistically pursuing my outlet tester I bench tested a neon lamp driven from a resistive voltage divider that would illuminate for 240V but remain dark for 120V.

A decent VOM can confirm AC voltage pretty competently.

JR

Completely agree.  I'm looking into the SureTest for the voltage drop under load ability as well as the frequency measurement, as well as some of the other test functions that the $2 outlet tester can't do.
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