When moving an existing outlet for a light over a sink to an overhead light can you pig tail copper wire onto the existing wire? Or is there something special you need to do first?

Read this Aluminum wiring I don't recommend doing this but sometimes you have to connect these 2 wires. Solder or a crimped collar can be used but not just twisting and tapping.

As reference points, please see NEC 110.14 "Electrical Connections" and 110.14 (B) "Splices".

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