Difference between 通常, 普通, 正常 and 平常

[ly2kutd1552]

I understand that they all mean normal but can they all be used interchangeably?
I've only managed to pick up a few subtle differences but I'm not sure if I'm right.

通常　つうじょう
I've seen this a lot on products and goods. Probably used on items and objects maybe?

普通　ふつう
Used mainly to describe people If I'm not mistaken?

The latter 2 I'm not too sure about however judging them based on their kanji, maybe 正常 has got to do with describing normal ways of doing things and 平常 is used for time and habits?

正常　せいじょう
平常　へいじょう

Would really appreciate if somebody could explain the nuances

[community.japanese]

Hello ly2kutd1552 san,
通常means ‘usually, normally, generally, as a rule’ and sounds formal.
For example,
通常国会（as ordinary session of the Diet）
通常兵器（Conventional weapon）
普通 means ‘usually or commonly’ and is used in more in formal situation.
For example,
お葬式には普通黒を着る．（Black is generally worn at funerals.）
そういうことは普通に起こることです。（The sort of thing occurs very commonly.）
正常 means ‘normality, regular’ and may be used for describing medical situation or personality.
新幹線は翌日正常に戻った。（The shinkansen got back on its normal schedule the next day）．You can use　通常 ,普通 and 平常 in this case.
平常 means ‘normal , normality’.
For example,
時間割は平常に戻った。（The schedule returned to normal．）
通常、普通can be used for this.
Yuki 由紀
Team JapanesePod101.com

[ly2kutd1552]

Ah I think I see the subtle differences now. Thank you Yuki sensei.

[community.japanese]

Ly2kutd1552 san,
I am happy you could understood them.
Douitashimashite.
Yuki 　由紀
Team JapanesePod101.com