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I installed two outdoor garage lights using 14/2 MC Armorlite Cable. The lights are only 8.8 watts and have day/night sensors. I connected the wiring to a garage door opener dedicated 20 amp circuit on the ceiling. This circuit has one duplex 20 amp receptacle for the garage door opener plug. The new outdoor lights 14/2 wires are fed into that box. I now realize that the wiring is not correct. I should have used 12/2 wiring. Upon advice from a friend/electrician I replaced the 20 amp breaker with a 15 amp breaker and replaced the 20 amp receptacle with a 15 amp receptacle. Is this allowed? For safety, should I replace the wiring from the outdoor lights to the garage door receptacle with 12/2 wire? Thank you for your advice.

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    I assume you don't have a garage door opener right now (i.e., hardwired into the same circuit). If you do, post the model # so we can check the specs as running it on a 15A circuit may be against the manufacturer's directions. – manassehkatz-Moving 2 Codidact May 24 '20 at 19:58
  • I have a Liftmaster Elite Model 3850. It is plugged into the 15 amp receptacle (the dedicated 15 amp circuit. – Johnmus May 24 '20 at 20:12
  • Interesting. I found the owner's manual online very easily, but it didn't list the specs (unless I missed it) of how much power is needed. But the diagram clearly shows a 15A receptacle (and also allows for hardwiring) and based on 3/4 HP, etc. it should be fine on a 15A circuit. So you're set. – manassehkatz-Moving 2 Codidact May 24 '20 at 20:19
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Your friend gave you good advice. Breakers are sized by the smallest wire in the circuit. Since you added 14/2 to the circuit, a 15 AMP breaker is the maximum allowed. Replacing the receptacle was needed too. The 14/2 you installed is fine since you replaced the breaker.

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Based on my experience (I am not a licensed electrician), I think everything you did is OK. Key was to replace the 20 A breaker with a 15 A breaker. Only other thing you might want to do is to make a note in the circuit breaker panel to the effect that "Circuit [put the number of you circuit breaker here] feeds #14 wiring", or something similar, so that someone doesn't come along in the future and seeing 12 gauge conductors going into the circuit breaker, think they can up the breaker to 20 A.

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