Help! - problem with a home light circuit

Thread Starter


Joined Jan 28, 2017
I hope to get some help here for a simple home circuit problem...

My kitchen table light with a dimmable switch used to be working fine, until when I changed to an LED light bulb, the dim switch won't totally turn off the light - at off position, the LED light flicks. I read online and saw discussions about the switch not compatible with the light bulb, so I went to HomeDepot bought a new Lutron LED dimmable switch. After changing that, the problem persists, and putting an old incandescent light bulb, it won't even be turned on.

Then I noticed something weird: putting the LED light bulb on, and when the switch is not even connected, the light would still flicking or stay on with very low light, as if there's a "leak" of electricity to the light. But how this could be? - the hot and neutral wires are not even connected at the switch box? Where does the "leak" power come from?

Now I am confused: how come the old switch with the old incandescent light bulb used work just fine on the same circuit, but now with no wire connected at the switch box, either the old incandescent light bulb or the LED light bulb will dimly glow? What can cause this "leak", and how do I fix this?

Thanks for any suggestions!


Joined Aug 23, 2012
We need some more info about the table light and the dimmable switch, and the info of LED light bulb, the wattage/voltage/current?

You could take some photos and compress them to 800x600 *.jpg and upload them.
Hi BillL:

Well, here's the scoop, or at least part of it. An incandescent lamp has a resistance about 10-15x less than when it's hot. A dimmer (SCR/TRIAC) messes with the firing angle of the AC voltage. That component "leaks" or put in another way, it requires a minimum load to completely shut off. Minimum loads can be as high as about 100 mA.

If the incandescent dimmer is "smart", but I doubt it is, the rotation of the dial can correspond to V^2 and the light bulb characteristic to get linear dimming. e.g. 0-270 deg = 0 to 100% dimming of the lamp. In paractice, this does not happen.

AC Dimmable LEDS basically suck. Some work. Some don't. Some explanations are here:

I recently ran into this phenomenon with an Insteon or UPB home automation switch, DIM LED with the switch on/off. I could add a 25 W incandescent lamp in the fixture and all is well. It was an outdoor fixture with a non-dimmable lamp. I expected the UPB over power line device to to be non-dimming, but it isn't.

A LED replacement for the automobile trunk light didn't work out either. There's automation there too, where if the lamps are on too long they turn off. The lamps also slowly dim when thy turn on and off, but not the trunk light. For now, if the trunk light comes on dim, I have to open the door, then the trunk light brightens. So, I need to add a minimum load to the trunk lamp. I just haven't done that yet. It's winter.

I bought another non-dimmable, but low voltage lamp. Sold as a 12V lamp, but it really works from 5 to 35 volts at full brightness. There is a dim pin on the IC used in the lamp, but I haven't tried to do anything with it.

Currently, it a crap shoot:

LED lamps are all over the map with performance. One never made it through shipping. It's an eggshell. The replaced lamp is now dead installed in a ceiling fixture.

One manufacturer, now defunct, made "Super LEDS" as far as I'm concerned. They were heavy and had liquid cooling and were available as 3-way, but they were $50.00+ USD or more.

So, adding a minimum resistive load is one way to fix this. How much unknown, but a flame proof resistor should be used. It's possible that a 5 to 7W night light would do it.

FWIW: I BELIEVE the NEC is starting to require neutrals in the switch side of the circuits to accommodate automation systems.
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Thread Starter


Joined Jan 28, 2017
Hi, KSS:

Thanks to your reply and information! Appreciated!

What I did next was, while the on/off switch was disconnected, I disconnected the whole light fixture, and then connected an old incandescent light bulb to the hot and neutral wires directly, and the light bulb still dimly glowing. So I can tell now that it's not a problem of the LED light bulb (since I am connecting an incandescent light to it), and it's not a problem of the switch either (since the wires are not even connected to the switch - both hot and neutral wires are left open and dangling in the air). Now this is very weird indeed, especially this used to work, for 20+ years!


Joined Sep 9, 2010
That's potentially dangerous situation. The current leaking through the bulb might be leaking to ground instead of the neutral wire. This could make metal parts of your ground system partially "hot". So, proceed with care.


Joined Oct 15, 2009
Measure voltage between hot/ground to confirm is correct
Try another incandescent..

And are you sure you aren't grabbing the traveler wire? (Is this a 3way switch?)

Thread Starter


Joined Jan 28, 2017
Thank you all for the help!

To reducing confusion and guessing, here let me show more details and exactly what's going on with photos, so you can help me making the right diagnose...

1) First, here's the switch box, where I disconnected the switch that controls the table light entirely, leaving the hot and neutral wires open:


2) Here's the kitchen table light fixture at the kitchen ceiling, where I disconnected the light fixture entirely, and also left the hot and neutral wires open: (ground wire is still connected but that really doesn't matter, as you will see later)

3) I made a light socket with two clippers to test with lights, and here I connected an LED light bulb directly to the hot and neutral wires, and the LED light bulk dimly lit up (not full intensity), and it also flicks (not enough voltage or current?):

Thread Starter


Joined Jan 28, 2017

4) Now, I connected a multimeter to the two terminals to see what's going on: when there's no load (light bulb taken away), it shows it has 120V across:

5) And it appears draw 17 AMPs (I don't understand why this is so, as there's no load connected to it at this moment):

7) Connecting a 75W incandescent light bulb, the current goes to 0 AMP - I guess we can assume the current flows to the light bulb so the meter measures 0 AMP, when the incandescent light bulb is dimly on:

8) And it shows 7 volts across the terminals when measure the voltage:

9) Switch to an LED light bulb, it shows the voltage to be 35 volts when the LED light is only dimly lit:

Thread Starter


Joined Jan 28, 2017

10) Looking inside the switch box:

As you saw early in the first photo: there are 3 switches at the switch box, and one of them (on the right) is on the same circuit breaker as this kitchen table light fixture that I am having problems, and that switch connects to kitchen countertop lights - when the circuit breaker is pulled open, both kitchen table light and countertop lights are all off.

So I was thinking there maybe two possible causes of this problem of the table light circuit "leaks" electricity:

1. The ground wire for the table light fixture is not connected to the copper ground wire inside the switch box.

I connected it to the ground and that didn't make any difference in solving the problem. So that doesn't seem to be the problem cause. Maybe due to there's a "floating current" somewhere can't return to the ground that cause the LED light to be on. So, I connected the ground wire to the copper ground wires of the other wires. It made no difference: when I made a jump from the table circuit ground wire to the copper wires, the LED light still flickering. So this is not the cause of the problem.

2. The other switch that controls the countertop lights, is an old dimmable switch, and some of the countertop lights are LED lights, so there maybe current leak in that circuit, as some people claim that dimmable switches always has power on, or the LED lights "leaks" current. However, everything works fine for the countertop lights: the lights are dimmed properly, and can be turned off totally by its switch. And most importantly, the two circuits don't seemed to be connected - they have seperate wires, even though they are controlled by the same circuit breaker panel switch (maybe share the same ground or same hot or same neutral), so it seems to me that this is also not the cause of the problem.

So the question becomes, why the wires at the table light fixture is hot, when the control switch is actually open (not connected to anything at the switch box)? And why when it shows it is having 120 volts across, it can only dimly light up light bulbs but not full intensity? Would the other circuit share the same break panel switch be the cause? Could be something wrong at the break panel?

So even as an electrical engineer by training, I am now confused and at loss :)

More insights and suggestions are appreciated!



#4 can happen and there's nothing wrong. It's hard to image, but it can.

Note that this meter has a Low Z mode. This is what electricians should be using. The high impedance meter can pick up leakages from say a switching power supply filter on another appliance. When you draw a tiny bit of current, the voltage ceases. It's not necessarily a problem.

When the voltage ends up being ~60 V, then that's a problem. I'm not sure your interested as to how that can happen?

#7: You can't measure current that way with this meter. You need one wire to pass through the center of the jaws for best accuracy. That reading has to be totally bogus. Use your light bulb as a load and open the jaws so one lead of the light bulb pigtail is centered in the jaw with the light on.

Thread Starter


Joined Jan 28, 2017
Hi, KSS:

Thank you very much for your reply and comments!

Regarding #4, I thought when the circuit is open (the wires at the switch is not connected), there should be power flow to the wires, and therefore there won't be a voltage drop. Reading more online about the home wiring circuits, you maybe right that this is normal.

And I am totally getting what you said about need to have a low Z mode meter to pick up the leaks from elsewhere, such as the neighboring counter top lights that has LED lights in the circuit and a dimmable switch. Now the only cause I can think of it, I think it's likely from that circuit - possible the common neutral or hot at the power surge panel, unless the power panel where the surge strip switch that controls this circuit is faulty.

Now sure what you mean by voltage ends up being to 60V, and how that could impact this problem.

Yes, you are absolutely right about #7: my goof that I forgot that you can't measure current that way with parallel connection - the load has to be in serial with the circuit. Electricity 101, doh! :)

Thanks again!

In post #9, I need you to inspect this box and the ceiling box very carefully and look for a few things:

1) Make sure all twisted ground wires have wire nuts. If they do not, you may have to remake the joint and out a wire nut on the wires. So, you can wirenut the bare grounds together and "pigtail" them to the switch box.
2) Make sure that the box is also grounded.
3) If you are using crimp connectors on any solid wire, loose them. I don't even think crimp is allowed.
4) Unless your using a special outlet/switch, your not allowed to relay on the attachment screw of the switch to make contact to ground.
5) Newer boxes have threaded holes for a ground screw, otherwise you have to use ground clips.

A non-wirenutted ground can cause you an awful amount of grief.

So the switches generally need to be grounded, so if they are loose, they still have a ground. The metal box has to have a ground and it's a real pain to do this.

I'm going to TRY to explain something. See The URL has been modified to open to the right page.

Note that the leakage current is high. 0.4 mA for VB models. This filter has an intentional leak to ground.
If the ground disapears at say some daisy chained outlet, that leak "floats" the ground bus on "some" of the outlets (The ones with no ground).

Note the electrical schematic where the two capacitors are connected to ground. 0.4 mA to ground can mean an effective R to ground of R=120/0.4 mA or ~< 1200 ohms. Another way to look at it, is that those two capacitors connected to ground are very high value resistors. Let's even call them 1 M ohm. If the caps are the same and have approximately the same resistance, that output ground point could be at approximately 60 V with respect to a real ground, if it wasn't connected to ground.

So, "stray voltages" and currents are both normal and abnormal. They can be caused by cables running next to each other. When they are near 1/2 the line voltage, they are suspicious.

I'll let you munch on this for a while. I'll look at what you said in more detail also.


Joined Aug 16, 2016
Switches don't have a hot and neutral.
It's just hot and not hot yet, unless you flip the switch then it's hot and hot.

Typically in my country the hot wires run to the light first, then the switch.
It's also not typical to see a black and white wire connected to a switch, unless you have a 3 way.
I can't see enough of your switch box to know what's going on, you would have to pull out the other switches to see the wires and cables clearly.

Be careful sir.

Thread Starter


Joined Jan 28, 2017
KSS and Travm:

Thank you both for your comments and suggestions! Appreciated your help!

Just to close the loop here for this particular case.... I couldn't figured it and hired an electrician from HomAdvisor, and he came took a look at the switch box and the wires, and said that it looks like there maybe low voltage circuit affect this light circuit, and he said that I have a specialist in town, one of the best low voltage electrician, and I''ll let you call them to come fix this. So I called the other "specialist" company, and I asked the owner and their electrician read this thread there, so they could have an idea on what's the possible cause. They replied to me saying that this is beyond their capability and they are unable to work on this.

Since I am out of option on what to do next, I asked my window contractor who has some electrician experience to take a look, and he suspected that this might be a 3-way switch circuit, and asked me where's the other switch. I said I never knew there's another switch for this light. So we look around the kitchen, and found there's indeed another switch on the side of the kitchen wall. We opened that switch box, and I connected that light bulb to the ceiling, and the moment we cut the wire on that 2nd switch, the light went off! So we immediately knew that it's the faulty 2nd switch in this 3-way switch circuit was leaking the electricity, causing the light to be on even if the other switch was not connected. Replacing that faulty switch fixed the problem. Doh!

And it was fixed by a general contractor who has one year electrician apprentice training, after two professional electricians deemed unsolvable by them. Not instilling much confidence in the professionals, you know :)

Case finally closed here.

Thanks everyone!


Joined Sep 9, 2010
What the "pros" knew is that it might take too long for what they felt they could charge you. In my experience that's what the so-called pros do - a mediocre to poor quality job but fast. I can usually do a better job myself but I take too long.