replacing overhead light fail

October 30, 2016 9:28 AM

Overhead light with obscure bulbs long burned out so I don't know if it worked recently. Removed same. Confirm with voltage tester that hot wire is hot, neutral wire neutral, ground wire firmly attached to box. Installed new lighting fixture with LED bulbs. Put on juice. Light goes on for half a second, then died. Uninstall, check lights & fixture with known power, works fine. Repeat. Connections appear firm. (I've done this before.) Brief light, fade. Repeat. No light. Works fine elsewhere. Thoughts?

(Wall switch Lutron, if that matters)

By "Thoughts?", I mean, for obvious oversights before I call the electrician.

posted by IndigoJones to Home & Garden (11 answers total)

So the LED bulbs are not shot after the experiment? Your "repeat" session was done using the same equipment?

My guess is the wall switch is a dimmer and the LEDs are not dimmable ones.
posted by Namlit at 9:33 AM on October 30, 2016 [2 favorites]

Do you have 110V at the fixture?
posted by humboldt32 at 9:40 AM on October 30, 2016

Response by poster: Good points. LEDs are in fact dimmable (we have the same fixture and lamps on a rheostats elsewhere), switch is not, and power is 110.
posted by IndigoJones at 10:01 AM on October 30, 2016

I'd hazard a guess that there is a terrible connection somewhere such that while 110vac appears at the hot with a tester, it's actually not able to supply any current whatsoever. Maybe try it with a normal tungsten bulb/pigtail fixture just to rule out something fishy regarding the LED? are there other connections in a box somewhere in-between the fixture, switch, and breaker that you can check? corroded connection within an electrical nut somewhere, maybe...
posted by BillMcMurdo at 10:09 AM on October 30, 2016 [1 favorite]

Voltage meters (especially digital ones) typically draw ridiculously low currents, and can easily give a full-voltage reading on a circuit point that has only the most tenuous of connections to the supply. For testing mains circuitry, especially lamp fittings, you're better off with a known-good incandescent lightbulb.
posted by flabdablet at 10:14 AM on October 30, 2016 [1 favorite]

Is the problem repeatable? IE: if you hooked the light back up does it do the same thing?

If so try putting your meter in parallel with the light and see if you still have 110V.
posted by Mitheral at 12:19 PM on October 30, 2016

Response by poster: All good points, I will address accordingly. Thank you very much.
posted by IndigoJones at 12:55 PM on October 30, 2016

Best answer: Sounds like you're discharging a capacitor through the LED.

I know some starter/ballasts for fluorescents incorporate capacitors, but not exactly how they're set up -- could the switch be wired for fluorescents?
posted by jamjam at 1:04 PM on October 30, 2016

Response by poster: could the switch be wired for fluorescents?

I do not know! I shall check into it. Many thanks
posted by IndigoJones at 4:30 PM on October 30, 2016

Best answer: Try an incandescent bulb.

If there is a loose or corroded connection somewhere, the incandescent bulb won’t light. Turn the switch off promptly if that happens because you don’t want that bad connection heating up and starting a fire.

If the incandescent bulb does light, the problem is that the switches don’t work with low‐power lamps. Some switches have relays that require a certain current to stay latched. LEDs don’t draw enough current, so the switch doesn’t stay on. You’ll need to replace the switches (or at least their relays) with something that’s LED compatible. These days, an electrician will have experience with this problem.
posted by Fongotskilernie at 3:50 AM on October 31, 2016

Response by poster: Turns out switching the switch did the trick. Life is good again, and many thanks to all.
posted by IndigoJones at 7:33 AM on November 18, 2016