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Cooking with Timer, Grama Switch

Is it permissible to place uncooked food in an oven that will turn on on Shabbos with a timer (assuming there’s no Muktza issue)?
Similarly, is it permissible remove a plastic blocker on Shabbos if as a result a light will go on later on? The light pulses that will turn on the light will only be omitted at some later moment of time.
Thank you.


1. The Chazon Ish [O:C 38-2] as interpreted by Shoneh Halachos [R’ Chaim Kanievsky O:C 254:11] forbids putting uncooked or even cooked food in an oven on Shabbos, that will go on later in the day with a timer. However permits to place the food before Shabbos in one of 2 scenarios: the food is already cooked כמאכל בן דרוסאי, or the oven is prepared to avoid the problem of שהייה, by means of plastering it shut. His point is that while there is no problem of bishul by putting the food before Shabbos there is still a problem of creating a situation of שהייה, which creates a concern of שמא יחתה, adjusting the flame. Practically this would mean in our ovens it would be prohibited to put uncooked food before Shabbos which will go on through a timer.

2. While removing a random barrier to allow for pulses to pass through may be a grama, grama is in fact forbidden Rabinically on Shabbos, see O:C 334:22. This case may be comparable to the discussion in the poskim in the begining of O:C 277, with regards to opening a door which will allow wind to enter and blow out a candle on the other side. The Mishna Brura [sk 3] quotes opinions that this forbidden even when wind is not blowing at that minute.

In the case of the new so called “kosher switch” there is even more reason for concern. Once a device is set up to harness and use electricity in a normal fashion, such as a light switch that works as well as a normal light switch, this may be considered Maleches Machaheves, and forbidden according to Torah law. This being so even if the inner workings are based on “grama” technology. This is similar to the melacha of Zoreh which is technically done with grama and yet considered a full fledged melacha.


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