Answer: 1 1p is used for lighting. There is nothing wrong with the traditional practice. There is also 1p + N, which is not necessary. There is no leakage for lighting.

2. In fact, 1p + n is good. Switches like DPN have the same module as 1p switches!

3. 1p is generally used for lighting. The Residential Code mentions that the lighting of residential toilet should be equipped with leakage protection, so the lighting circuit of toilet can be equipped with 1p + n leakage protection. However, the drawing review does not mention that we generally use 1p lighting.