Electric installation rules in Japan

I'm sure there are rules when it comes to electric installations in Japan. I know the rules in Germany, but the rules in Japan are unknown to me. E.g. where to route electric cables.

Are there any documents in non-Japanese for this? Are there any rules which are being followed when it comes to electric installation work?

In a detached house or in an apartment unit? If it's an apartment building, and if you are thinking of running something inside the walls, it might be better to get a professional (meaning a licensed electrician) to do it for you, as it might affect other occupants' units.

Mind you, my spouse comes from your country, and he tries to fix everything (as he used to do back in Germany), but every time we go to buy some parts and little fixtures to do that, we get suspicious looks from the shops who tell us that, um, those are normally sold to electrical shops/professionals only...