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Light bulbs on our kitchen lighting circuit need frequent replacing (lasting only a few months.) All other circuits in the house behave normally. There are three switch legs on this circuit:

  1. 6 recessed lights, on a 3-way switch, with LED bulbs. Distance from switch to first light is ~10'. Each can is ~3' from the next.
  2. 5 pendant lights, on a single dimmer, incandescent bulbs. Distance from switch to first light is ~15'. Pendants are ~3' apart and ~5.5' long.
  3. Chandelier with 5 light sockets, on a single dimmer, incandescent bulbs. Distance from switch to light fixture is ~15'. Light sockets are ~6' from ceiling.

An electrician came out and discovered that the voltage at each switch is 120v, yet each light socket only reads 113v. The electrician checked in the attic and didn't see anything odd; the wires looked fine, no extraneous junction boxes, no damage, etc... The advice was to try out bulbs rated for 110v instead of 120v or re-run the switch legs.

What could cause such a voltage drop over short runs and three distinct switch legs? Do I have any other options besides the two offered by the electrician?

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    Could it be your meter? Also some are on dimmers, you'd expect those to be lower because of the dimmer. Some dimmers don't have a bypass mode (or, some users don't know you have to push past a detent to get there). – Harper Jul 10 '17 at 20:55
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    Which lights are burning out at an accelerated rate? LEDs or incandescents? – wallyk Jul 10 '17 at 23:50
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    Wait... LEDs? My money's on you're getting voltage spikes. The up-side kind, not the down-side, which in this case is bad. Even though I upvoted Kris (and the other two), I don't think it's an "over-voltage on the opposite phase", it's simply voltage spikes from your power company. Are you ever home 9-5 on a weekday and seen incandescent lights (that aren't on a dimmer) get brighter for a sec or two? – Mazura Jul 11 '17 at 0:05
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    "Had a problem with burnt out electronics in an apartment once, turned out to be a dropped neutral at the service. Test the voltage at a few different outlets, and watch for both high and low voltages." – Tester101♦ Strange problems that might be due to wiring - "Some better-quality UPSs allow you to log voltage over time, and perhaps events like spikes or surges, on a connected PC." –RedGrittyBrick – Mazura Jul 11 '17 at 0:24
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    Ok, I take it all back. It is an imbalance but it's caused by a crappy neutral connection. Impact of Floating Neutral in Power Distribution That's my story and I'm sticking to it because I'm outta ideas. "No spikes, just dips from the A/C starting" ... guess what happens when it stops. I think you either have too small a incoming service or a bad neutral. – Mazura Jul 11 '17 at 0:34
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It's a floating neutral.

But it's only the one circuit.

Find, re-strip, re-splice, and tighten down all of that circuit's neutral connections. If it goes directly through an outlet, pigtail it.

  • The next question I'd be asking myself is whether evidence of a floating neutral indicates a poor ground... – Mazura Jul 11 '17 at 0:55
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    That definitely sounds plausible to me. It's the only explanation of why an apparent undervoltage could kill LED lights -- if it periodically switches to being an overvoltage instead. I've seen this myself in a friend's house, and just tightening all the neutral connectors made the problem go away. – Jules Jul 11 '17 at 1:17
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In residential interior wiring, voltage irregularities generally are only a concern when over-voltages are seen and not under-voltages. Incidentally however, when there is an under-voltage, there is usually an over-voltage on the opposite phase somewhere else to balance it out.

113V is fine. Light bulbs, except for the LEDs, are pure resistive loads and will not burn up from under-voltages. Now 130V would be a problem if the bulb is not rated for 130V.

I would also consider hiring a different electrician as what he suggested is nonsense.

  • We also had the problem before switching the recessed lights to LED. Multiple bulbs needed replacing shortly after we moved in, which is when we decided to switch all 6 recessed to LED. – Mike Chale Jul 10 '17 at 20:26
  • I see. Perhaps the dimmer is the problem. Or light sockets. See my edit above. – Kris Jul 10 '17 at 20:29
  • Sockets were the 1st thing checked. After seeing 113v, he moved to the junction panel and then the switches. Should I check wiring in each fixture box? It seems odd to me that I have this problem on 3 separate switch legs. – Mike Chale Jul 10 '17 at 20:35
  • 113V is fine. Light bulbs ( except for the LED) are pure resistive loads and will not burn up from under-voltages. Now 130V would be a problem if the bulb is not rated for 130V – Kris Jul 10 '17 at 20:49
  • +1 for getting a different electrician. Incandescent doesn't care about getting a couple of volts less than expected. They just burn a tad less bright and last a lot longer. He should've known. – Mast Jul 12 '17 at 12:40
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Everything you are saying depends on where the electrician checked the voltages. Dimmers will affect the voltages on the load side. So did the electrician check for voltage drop across the dimmers themselves? If there is a drop it would be there. The other thing that causes abnormal voltage drop are joints not making a solid electrical connection. So look for loose wires or corrosion or anything that would cause the drop at connection and splices. On the least likely side you might check to see if the circuits cross an area that produces a high amount of heat. The only thing a 113V load would do to an incandescent is make the lamp put out less light and actually burn cooler.

I know this may sound a little snobbish but we have found the main reason incandescent lights burn out at an abnormal rate is that they are poorly manufactured lamps. The other main reason is a lot of surges from the utility company. Such as when you are in a new development and there is construction all around you. In construction, before energy management codes took effect we installed incandescent lamps using 130V filaments. It's a heavier filament and does not burn out for a long time. Unfortunately these are not available to the normal consumer and all the advertising about longer lasting lamps you see on the labels from retail outlets are generally hogwash. I know since over the years I and the companies I have owned and worked for have bought every style imaginable only to find there are no noticeable changes in longevity worth the extra cost.

You might try going to LED but if you do make sure your dimmers match.

Hope this helps.

  • The electrician measured 113v at the socket and 120v at the switch, but I'm not sure if measurements were done across the switch. These aren't dollar store light bulbs, but they're also not the most expensive things out there. The LED bulbs don't seem to be doing any better on this circuit. – Mike Chale Jul 10 '17 at 21:52
  • Are these LEDs in an enclosed fixture? If so, the LEDs may be overheated and having a shorter lifetime. – Jim Stewart Jul 10 '17 at 22:50
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    We just moved in and all these lights are going out... That's because they came out of a bucket in the realtor's trunk. +1 – Mazura Jul 10 '17 at 23:11
  • @JimStewart They're standard recessed cans, not fully enclosed. – Mike Chale Jul 10 '17 at 23:32
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    @Mazura My replacement bulbs aren't lasting either, though – Mike Chale Jul 10 '17 at 23:32
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Many LED lights are not equipped to deal with dimmers and those that are need dimmers rated for LED loads. Since you replaced the existing bulbs with LEDs I bet you have the wrong dimmers. Further since you mentioned a seven volt drop over a short distance I bet you have really old dimmers as newer dimmers do not show a voltage drop when full on. I would recommend one of the following:

  • go back to incandescent bulbs.
  • replace the dimmers with switches.
  • replace both dimmers and led fixtures with ones known to work together.
  • replace the dimmers with blank plates and use self dimming bulbs.
  • The LED bulbs aren't on a dimmer, though there are dimmers on the circuit. Would they still have an impact? – Mike Chale Jul 10 '17 at 23:35
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    Are you sure they are not on a dimmer? Your description was textbook dimmer kills LED. If they are not on a dimmer, you have a real problem in your wiring (not the 113v that is fine, but the voltage drop). I would check the switches (corroded contacts can cause voltage drop and are a fire hazard), the wire nuts and the fixtures. if you have or can borrow a heat sensitive camera it will locate the hot spots which is where your problem is. But if you aren't on a dimmer you are either getting crap LEDs or getting them too hot. – hildred Jul 11 '17 at 0:13
  • LED are definitely on regular 3-way switches. Will look into an IR camera and check wiring myself. – Mike Chale Jul 11 '17 at 0:15
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  1. As mentioned above check the wiring for a floating neutral, bad grounds via a polarity checker.
  2. You might also be getting spikes on the line from anything with a motor eg: an appliance (particularly an old appliance) or treadmill :)
  3. Check each socket for rust or corrosion
  4. Check each ground for rust, corrosion or loose connection
  5. Go to the fuse box and pull the the fuse or breaker (electrician required :)

Note, IMHO, 80% of electrical issues are due to rust or corrosion.

Note, Note, RESPECT electricity and turn OFF the circuit before any cleaning, removal, etc.

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