14/2 wire at ends of long run

Question

I was messing around in the attic  evaluating our wiring  and found that we have a couple of lighting circuits that, at their extreme ends, employ a bit of 14/2 wire, greater than 50 feet from the panel box.
In some cases it's the switch legs only, and in others  the final branch supplying a light AND its switch leg.  The majority of the circuit consists of 12/2 wire  and the breaker is 15A.  I don't think anything ends up much over 60 feet from the panel  unless you count both the hot send AND return from the switches. In which case there is at least one that ends up about 65 feet altogether from the panel.
I was thinking perhaps the fact that the majority of the circuit is 12/2 means the voltage drop will be negligible.  True?
Appreciate anyone providing a more educated opinion.

Ecnerwal · Accepted Answer

15A breaker, 14/2 is fine. Likely would be fine the whole way, but 12/2 is also fine, perhaps someone was overly concerned with voltage drop. Voltage drop is much less of an issue if you are using modern lightbulbs that draw much less power. If you love paying the power company to run your big-ol incandescent bulbs, voltage drop would be SLIGHTLY less with 12Ga than with 14Ga over that sort of distance.
So, if you had 1,440W of lights (12A, as much as you should have on a 15A lighting circuit since lights are a continuous load) all at the far end of one 65 foot cable, in the 14Ga case you have 115.9 Volts and in the 12Ga case you have 117.4 Volts, assuming you started with 120V at the breaker. A volt and a half difference - pretty much irrelevant.
In the actual case you probably have of smaller lighting loads supplied by different cables carrying less current, the differences would be even less.

manassehkatz-Moving 2 Codidact · Answer

I suspect a bit of the opposite:

Original wiring - with the last piece not installed yet was 12/2 on a 20A breaker.
At some point, someone added the last piece and used 14/2 wire. At that point they had to replace the 20A breaker with a 15A breaker.

Also possible that they did not replace the breaker, and a later inspection revealed the problem and rather than replace the 14/2 wire with 12/2, they replaced the breaker.
Either way, the result is perfectly safe. With modern LED lighting, you can light up a whole house with just a few amps, so a 15A circuit is just fine.

14/2 wire at ends of long run

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