Q. May I plug during Shabbos a cooking appliance into an outlet that is now not powered but will be turned on by a timer later on?

A. Horav Shlomo Miller’s Shlit”a opinion is that it is prohibited since it is a P’sik Reisha Denicha Lei, or an inevitable act that one desires. He would prohibit this in Yom Tov too.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a