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120 volt timer passes small amount of current when off. It's on Christmas outdoor LED lighting. The lights glow real dim when the timer goes to the off position. Does it on two different timers. Do I have a short in the lights or what might cause this?

  • Could you post a photo of any labels on the timer device? I'm curious to see if it has an FCC ID listed. – Greg Hill Dec 17 '19 at 19:35
  • It depends on the type of timer some use a small amount of current to run the clock or electronics and this small amount of power is enough to lite some LED’s what break timer do you have? I use an sto1 timer by intermatic they run on a cr2 battery for 2 years. – Ed Beal Dec 17 '19 at 19:56
  • Are these UL listed timers bought at a retil store? Or are they Amazon/eBay/AliExpress specials? – Harper - Reinstate Monica Dec 17 '19 at 21:55
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This is a common issue with LED lights, and we have a few questions about in regards to normal light bulbs, but nothing I remember that is specifically about Christmas lights.

Plug in timers (and some smart switches, motion detector switches, lighted switches, etc) need to get power from somewhere so they can operate. In the past, these devices have used the fact that incandescent bulbs need a ton of power to cheat the system a little bit. Even when the device is off, it's running a very small current through the lights so it can power its internal circuits.

The problem is that LEDs will glow with even a minuscule amount of current, so this little trick that was invisible in the past, now shows up as glowing LEDs. For Christmas lights, I would say it's no big deal, and just live with it. It's not going to cause a problem. They are cheap timers that are using a "vampire" method to steal power from the circuit.

If it's unacceptable, the only fix is to get a timer that says it will work with LEDs or a timer that is obviously powered by batteries. These will use AAA or AA batteries. A timer that only uses a coin cell is probably just using that battery for a timer backup and might still steal power from the lights.

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  • Thanks a lot - that explains it. It had me baffled. – Mark Carle Dec 18 '19 at 10:47
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There are 3 ways that a timer, motion detector, smart switch or other device that needs power when the controlled device is off can get power:

  • Leak through the main circuit (switched hot) This is what you currently have. It works great with incandescent bulbs. It does not work well with many other things, including LED lights.

  • Neutral This is preferred, by far. However, it is often not an easy thing to do in an older house because many switches do not have neutral available at the switch. The current NEC requires neutral to be available (or easily added via conduit) at all switches for exactly this reason. But in older houses it is a big problem as it is often quite a hassle to replace cables.

  • Ground This is cheating a bit. However, if designed properly and UL (or similar) Listed, it is OK. But you can't simply say "neutral and ground are almost the same so I'll hook up this timer's neutral wire to ground" - it may function but it is not safe unless designed to be installed that way.

Unfortunately, often the only way to tell what method a particular timer/switch/etc. uses is to carefully read the installation manual. Fortunately, those manuals are generally available from the manufacturer (and often from retailers such as Home Depot) online. If the instructions indicate a neutral is required, it is. If the instructions make a big deal about ground but there is no neutral connection then that is a strong indication that ground is being used instead of neutral. If the instructions indicate that the timer/switch/etc. is compatible with LED lighting then it is almost certainly using neutral or ground. On the other hand, if the instructions specifically exclude LED lighting then leaking current through switched hot is quite likely.

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Another solution: plug a small incandescent lamp into the timer, in parallel with the LED string. The current draw of the incandescent should keep the LED string from glowing when the timer is supposedly "off".

Ideally, this could be something as small as a 4W night light. But, the details of where you're installing this could make it impractical.

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  • Heh, I shouldn't have said "only fix". This is a good option if the extra bulb doesn't cause a problem (not sure why it would). – JPhi1618 Dec 17 '19 at 20:47
  • Thanks - will try that. – Mark Carle Dec 18 '19 at 10:47
  • Cool. Let us know if it works. – Daniel Griscom Dec 18 '19 at 10:59
  • Didn't Work??? By the way - same timer and lights last two years and no problems?? – Mark Carle Dec 18 '19 at 21:28
  • @MarkCarle Well, it was worth a shot. To get a better answer, please edit your question to include the information requested in the comments. – Daniel Griscom Dec 18 '19 at 21:38

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