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I have a surplus of 14/2 and a little bit of 14/3, and this project is price-sensitive, so I drew up this plan to make use of what I have on hand. It minimizes the length of 14/3 needed because that's all I have on hand. All switches and lights have neutrals and grounds accounted for - I just want to make sure I'm allowed to use a 14/2 cable as two travelers without a neutral.

diagram

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    No, see NEC 300.3. /3 should go straight between the switches and need not stop at any lamps. 14/2 from either switch to the lamps. Aug 9 at 23:47
  • I see, the issue is about impedance. Is this also the reason why a neutral is needed at the switch even if it is unused - the neutral picks up the induction familyhandyman.com/wp-content/uploads/2018/04/…
    – Frambot
    Aug 10 at 0:14
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    That's not quite the issue. Neutral is required in new wiring to switches to allow for future upgrades to switches that need neutral, eg Smart, lit, timed switches. The layout you drew satisfies that requirement but creates an asymmetric current path, which is not allowed. You're not just adding an unused neutral to help with future upgrades. That would be good. You're using a neutral in a way that creates a loop, not running in the same cable along the same path as the live conductor. That's not good. You shouldn't confuse/conflate the two requirements.
    – jay613
    Aug 10 at 0:29
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This is not allowed because it violates the rule that in any cable there must be two conductors carrying equal current in opposite directions so the magnetic fields cancel. That T- T Loop top right would have one traveler carrying current, no current in the other, and no neutral present carrying current in the opposite direction.

The time varying magnetic field around the cable could induce currents in nearby conductors and cause heating.

EDIT

Since you are going to have to buy more cable, consider getting 14/4 + gnd and connecting the two switches in the arrangement called three-wire control. This gives a neutral and a constant line hot in both switch boxes. I recently came across an article¹ for a UK audience touting three wire control as superior to the traditional two wire control for connecting a pair of 3-way switches. I don't know if this is being done in the US.

The presence of both a line hot and a neutral in all switch boxes may be useful in the future, and the immediate benefit would be that you could easily extend the circuit to put a receptacle in the wall below. Such a receptacle would be independent of the two 3-way switches.

¹https://www.electronicshub.org/2-way-switch-wiring/

Three wire control of pair of 3-way switches

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    While I agree with the explanation, and you bring up very a good point, quantitatively the OP or other readers need not panic, as there is not much cooking at only a few hundred mA of current, and quite a large loop area of at least 1/2in x 10ft.
    – P2000
    Aug 10 at 0:30
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    +1, but heating is not the problem - not unless there are enough amps going through the cable to melt it. The reason to avoid loops is entirely to do with EM noise pollution.
    – J...
    Aug 10 at 12:35
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    @J... Heating really is a problem. You might install a circuit with a 5W LED today. But the circuit, by definition, can handle 15A, 12A continuous. So the next owner might decide to put in a few hundred W of floodlights. Or reuse the existing wiring for a regular receptacle and plug in a 1500W heater. No way to predict future usage, so code is based on the maximum. Aug 10 at 14:19
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    @JimStewart Yes. In systems where three phase power, for example, is fed to a junction box in individual conductors (common around 400A+ drops) I've seen small aluminum plates fitted over a punchout in the steel with the strain clamps also aluminum, presumably to mitigate this. It can be a concern in EMT, also, at least at higher currents, so I'll perhaps temper some of my previous scepticism.
    – J...
    Aug 11 at 1:45
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    What you're describing is called a "California" or "Coast" 3-way in North American parlance -- it gives you always-hot and switched-hot at both ends at the price of not working with 4-way switching Aug 11 at 11:45

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