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I have a hallway light fixture with three switches. When the circuit is off, a small voltage persists to the fixture causing LED and CFL bulbs to stop working prematurely. It is believed that the phantom voltage is coming from induction between the traveler wires. Suggestions to my previous question regarding this situation involved using a resistor, relay, or other circuitry to bond the hot to ground. I'm not particularly fond of this idea because if something were to go wrong it could invalidate my insurance.

Last night I woke up with a crazy idea (yes, this has literally been keeping me awake at night), why not use a DPDT switch on the source end of the circuit to connect the open traveler to neutral. I've created the following diagram of what I intend:

4-way switch: line and neutral to travelers, 4-way switch travelers to travelers, 3-way switch travelers to fixture

Is this configuration allowed by code? Is there a name for this type of a multi-way switch setup?

Location: Utah, United States

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  • The upper green line is the earth ground attached to the chassis of switches and fixture. The left-most blue line is the hot and the lower grey line is the common/neutral. – psaxton Oct 13 '20 at 21:31
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    Without getting into the "will it work", travelers by definition are switched hots and should never be switched to neutral. Down the road, someone could hurt or worse with non standard wiring. – JACK Oct 13 '20 at 22:08
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Better idea: use a part listed for the job to bypass the errant current around the lights

Fortunately, there's a way to bypass the errant "phantom" current (from capacitive coupling through the parallel traveler wires) back to neutral without doing anything that'd void your insurance. Simply nut a Lutron LUT-MLC in between switched-hot and neutral at the first light fixture on the circuit; they're listed (as an appliance control) for use in mains wiring, so there's no need to worry about your insurance complaining.

As to your original idea...

While your original idea seems sound, it falls into a grey area of Code interpretation regarding the meaning of NEC 404.2(A), which was originally put in to prohibit dangerous Carter 3-way setups:

(A) Three-Way and Four-Way Switches. Three-way and four-way switches shall be wired so that all switching is done only in the ungrounded circuit conductor. Where in metal raceways or metal-armored cables, wiring between switches and outlets shall be in accordance with 300.20(A).

In your case, neutral is never broken by any switch (breaking the neutral with a multiway switch also violates NEC 404.2(B)), but simply connected to an otherwise floating traveler wire to short out a voltage that got coupled over by a parasitic capacitor. Note that this configuration doesn't parallel the neutral either, because the neutral-connected traveler and the actual neutral are connected to opposite sides of the load, which means that the normal issues with wires in parallel and NEC 310.10(H) don't apply here.

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  • Lutron LUT-MLC , new to me +1 – JACK Oct 14 '20 at 0:56
  • Thank you for explaining how it is a grey area for code. I do have one more dumb question: do I need to use the lutron smart switch to use this in accordance with manufacturer instructions? – psaxton Oct 14 '20 at 3:09
  • Also, by "ungrounded circuit conductor" in the code referring exclusively to the hot wire and switched travelers, or is that why this is grey? – psaxton Oct 14 '20 at 3:12
  • @psaxton -- the "ungrounded circuit conductor" means hot wire and travelers, yes. as to whether the listing is only valid in conjunction with the Lutron no-neutral switches is something that you'd have to ask your local inspectors, though... – ThreePhaseEel Oct 14 '20 at 3:14
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    The MLC is a nice solution! Basically it's a UL listed 470nF cap to shunt leakage from a no-neutral dimmer. The capacitive voltage divider in a 14/3 is 1nF/1nF per 100ft. Shunting it with 470nF should get rid of practically all the voltage. – P2000 Oct 14 '20 at 22:11
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Your first two switches in the sketch are set up to basically reverse the polarity between the hot and neutral. this is really not a thing in AC, more used to reverse DC motors. I doubt this is up to code (though ill leave it for the code experts to chime in), and IT IS NOT safe and i'm not sure what function it would provide you. Normally the neutral power leg doesn't tie into the switches at all (except for smart switches that need the power locally within their electronics).

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  • If there were a 3-way switch left of the 4 way switches and the travelers connected straight through, I believe this would be a standard 4 switch setup. What is not safe about it? Is there a switch configuration which will short hot to neutral? If so what is that configuration because I'm not seeing it? As specified in the question, the function I am attempting to provide is to bond the open traveler leg to neutral to stop the phantom voltages from burning out my light bulbs when the lights are supposed to be off. – psaxton Oct 13 '20 at 21:27
  • you actually measure a voltage across the bulb when its off? Or just across the two unterminated high impedance ends with no bulb present? – mark f Oct 13 '20 at 21:32
  • Yes, there is measurable voltage of about 40V when the circuit should be open (lights out). This causes the base of the lights to remain warm and an extremely faint glow of the lamps even when the circuit has been open for days. Within a matter of weeks, the bulbs will burn out. – psaxton Oct 13 '20 at 21:36
  • That sounds like something else going on, If the voltage is present with a load, its not "Phantom voltage" and indicates a real wiring issue some where. Is the main panel box perchance fed as part of a three phase set up? – mark f Oct 13 '20 at 21:42
  • No, there is no three phase. Thank you for your quick assistance. Have you taken a chance to read the dialogue of the original question? – psaxton Oct 13 '20 at 21:43

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