A home electrical question...

[Stevebx]

Thought I'd check here as there are a lot of experts that help out. I bought a place that has a light over a stairway, switch at bottom of stairs, switch at top. I noticed that the light is still on, very dim, when it should be off. I haven't wired a 3 way switch before so don't know what to look for.

[Harvard]

Drawing of wnjjs Stray Capacitance

[Harvard]

Quote from Health Canada on the topic of Electric Magnetic Fields (EMFs):

START QUOTE:
EMFs are invisible forces that surround electrical equipment, power cords, and wires that carry electricity, including outdoor power lines.

•Electric Fields: These are formed whenever a wire is plugged into an outlet, even when the appliance is not turned on. The higher the voltage, the stronger the electric field.

•Magnetic Fields: These are formed when electric current is flowing within a device or wire. The greater the current, the stronger the magnetic field.

EMFs can occur separately or together. For example, when you plug the power cord for a lamp into a wall socket, it creates an electric field along the cord. When you turn the lamp on, the flow of current through the cord creates a magnetic field. Meanwhile, the electric field is still present.
END QUOTE:

The physics of Capacitance is related to Electric Fields.
The physics of Inductance is related to Magnetic Fields.

[wnjj]

Harvard wrote:
I can see stray capacitance between hot conductors conducting enough leakage current to make a LED light glow in the dark.

That’s possible considering a 3-way circuit has a nice long run of wires parallel to each other in the same Romex jacket, 1 has power and 1 goes to the light.

This guy seems to think so: https://diy.stackexchange.com/questions/57578/is-this-really-inductive-capacitive-coupling-and-is-th...

[Harvard]

I can see stray capacitance between hot conductors conducting enough leakage current to make a LED light glow in the dark.

[philh]

pull the black wire off the switch, does the light go dim? If not, you have some other leakage which can be a nightmare to find.

[KD4UPL]

Is this a really old house, one that might have been wired in the 1940's or earlier?

[Stevebx]

There is no dimmer switch. Yes, I replaced the old bulb with a LED bulb. I've left it off for a full day and it still glows, visible only at night. I'll try switching it to an incandescent bulb and see what happens. It seems that if a switch is off, it should just be off, but maybe not?

As to being a "new" member after 18 years - I somehow lost my original ID and was given a new one. Not being tech savvy enough to get back to my original, I lost my history. Oh well, everyday is a new day.

[DavinD]

If you have a dimmer switch, especially smart switches and there is no neutral at the switch location, the dimmer could need to pass a small amount of current through the bulb to power its own functionality (Like it may have it's own LED to light up the switch). This is common with smart switches that work without a neutral wire. That small amount of current wouldn't be noticeable in an incandescent light, but may trigger a LED to glow.

[2oldman]

I replaced incan bulbs in the range top with LED, and now I can't shut them off. They get real dim, but never dark.

[opnspaces]

I had that problem with a fluorescent light but it was only on one of those old school switches that have a red LED glowing in them when off.

[Rick_Jay]

Stevebx,

Two questions, if I may?

Just out of curiosity, what type of bulb is in the fixture: incandescent, fluorescent, compact fluorescent or LED?

While technically a bulb should be completely dark when it's "off", I've seen some that seem to glow for a long time afterward, especially the fluorescents and some LEDs. In fact, we have an LED sign which when shut off, you can still see a slight glow coming from the LEDs when the room is otherwise completely dark. If I pull the plug, they go dark. Apparently just the potential across the bulbs/power supply is enough to allow a trickle current through them so they barely illuminate. I never observed this type of problem with an incandescent bulb.

Second question, while unusual for a stairway, is there a dimmer control on one of the switches?

~Rick

[CA_Traveler]

Bad switch or maybe a dimmer switch was installed are likely candidates. Miswired or failed wiring is also possible.

[2oldman]

New member after 18 years? wow.

[3_tons]

Heres a great tutorial:

https://www.familyhandyman.com/electrical/wiring-switches/how-to-wire-a-threeway-switch/

If the light is on dim, it may be the sign of a failing switch and power back feeding from ground.