When I turn "off" my bathroom vent fan, my shower light turns on momentarily until the fan stops spinning.

Both the light and the fan are wired in parallel on the same circuit.

If I drop the shower light (Utilitech 65-Watt Dimmable LED Recessed Retrofit Downlight) suspended in the air (i.e. the three prongs no longer touch the can), the problem goes away. If I push it back in the can, the problem returns.

At this point I've ruled out everything but paranormal activity.

  • I don't understand. Do the fan and light turn on together on the same switch? Are you saying the light was on the whole time, and is staying on until the fan stops turning? Or are they on separate switches? Commented Jul 26, 2018 at 1:30
  • Pay special attention to the grounding (ground wires, metal connections) up there. Anything special, weird or wrong? Commented Jul 26, 2018 at 1:31
  • The light and the fan are on the same breaker, but wired independently in parallel off the power bus to two ordinary light switches. So if the shower light is off, and you turn the fan on, then turn the fan off, the light turns on until the fan stops spinning even though the switch to the light is still off.
    – ShawnBob
    Commented Jul 26, 2018 at 15:50
  • How is the wiring done between switches and box? /3 cable, shared neutral to the fan/light? , separate neutrals from the switches? How about grounding, is there grounding all the way back to the panel? Fan and light only grounded to each other? Is ground bootlegged? Commented Jul 26, 2018 at 16:02

1 Answer 1


First, "until the fan stops spinning" is straightforward enough — a simple AC motor that is spinning but without power applied will act as a generator, supplying the electricity that the switched supply isn't any more. The higher efficiency of LED lighting — and the electronic LED driver circuits used — mean that they can run from lower voltages where an incandescent bulb would be too dim to see.

If your light and fan were on the same switch, this would be enough to explain things. But you imply they aren't because you say the light turns on rather than that it was already on.

There must be something electrically weird going on beyond what I've described so far, to completely explain things. I would suggest updating your question with photos of the interior of the fan and the light pulled apart, and if you have any type of “smart” switch rather than a simple toggle, give the details of that.

  • I may try to add some photos tonight, but the light is an integrated LED conversion kit, which has a dummy socket that screws into the can. The socket has approximately a foot of blk/wht wire and an orange push connector that connects to the unit. The unit has 3 (grounding) prongs which engage when it is pushed into the can.
    – ShawnBob
    Commented Jul 26, 2018 at 15:54
  • The switches are ordinary simple toggle switches.
    – ShawnBob
    Commented Jul 26, 2018 at 15:55
  • @ShawnBob Please edit your question to compile the information you're providing, rather than spreading it in comments. (I don't have any further ideas for my answer yet.)
    – Kevin Reid
    Commented Jul 26, 2018 at 16:31

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