I recently ran wiring for a flood light that shines over my deck. A friend who seemed to know what he was talking about told me I could "grab power" from a junction box to power the light.
The junction box has 12/2 wiring running through it and the wiring to the light is 14/2. This did not raise a question to me until I saw some faint "arcing" in the new light switch when I shut it off. The circuit in the panel is 20 amps, should I just run the new wiring to the box and put in a 15 amp breaker instead? Will this set up above cause an overloaded circuit? I have plenty of space in the box, I think my friend was trying to cut corners by doing it this way.

I recently ran wiring for a flood light that shines over my deck. A friend who seemed to know what he was talking about told me I could "grab power" from a junction box to power the light.
The junction box has 12/2 wiring running through it and the wiring to the light is 14/2. This did not raise a question to me until I saw some faint "arcing" in the new light switch when I shut it off. The curcuit in the panel is 20 amps, should I just run the new wiring to the box and put in a 15 amp breaker instead? Will this set up above cause an overloaded circuit? I have plenty of space in the box, I think my friend was tring to cut corners by doing it this way.
Grabbing the power from a box dictates that the wiring is the same size, in this case would be 12-2 w/gnd from the j-box. Also it would have been easy to use lighting with a dusk to dawn cell with motion sensor. Not that costly and lets you install it in the wall using a cut-in box. The hookup would not affect the inside wall circuit if it is wired in parallel to the existing circuit in the box without needing a control switch.