I recently visited Eretz Israel and stayed at an apartment which we rented from observant people. For warming food over Shabbos, they had an electric hot plate which was attached to a time clock. It would go on for a few hours Friday night and then shut off, and then go on again for a few hours near Shabbos lunch, and then shut off again. Is this permitted under Halachah.
Sincerely,
Bernard Segal
bsegal53@aol.com
We touched upon the topic of Shabbos clocks in Insights to Shabbos 18a. Below is what we wrote there, although it does not address all of the issues involved in your question.
With regard to your specific question what the Halachah is, since we do not render Halachic decisions, we recommend that you write to ask@ohr.org.il.
All the best,
Yisroel Shaw
P.S. Next time you visit Israel, come visit us at the Kollel!
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[FROM SHABBOS 18a:]
HALACHAH: USING A SHABBOS TIMER
OPINIONS: The Gemara cites a Beraisa that says that a person is allowed to open his sluice gate, before Shabbos, to allow water to flow into his garden or field on Shabbos. Also, mid'Oraisa one may put wheat into a watermill before Shabbos and have the mill grind the wheat all Shabbos. The Rabanan, however, forbid letting a mill operate on Shabbos because it makes too much noise (according to Rabah).
Can we learn from this Gemara whether or not it is permitted to set a Shabbos clock prior to Shabbos to perform Melachah on Shabbos?
(a) RAV MOSHE FEINSTEIN (IGROS MOSHE OC 4:60) forbids doing Melachah through a pre-set Shabbos timer. He says that although the Gemara permits certain actions to be done prior to Shabbos when the results of those actions will occur on Shabbos, that applies only when the process of the Melachah began prior to Shabbos. With Shabbos clocks, however, the entire Melachah begins on Shabbos.
Rav Moshe writes two reasons why it should be prohibited to use a Shabbos timer. 1) One may not tell a non-Jew to do Melachah for him on Shabbos. The same way, one may not "tell," or program, a mechanical device to do Melachah for him on Shabbos. 2) Rashi (DH she'Yitchanu) in our Sugya explains that having a millstone operate on Shabbos is forbidden because the noice that it makes is a disgrace to Shabbos, and if people were to have their mills running on Shabbos, they would be transgressing the Mitzvah of honoring the Shabbos. Similarly, setting a Shabbos timer to do Melachah on Shabbos is a disgrace to Shabbos.
Rav Moshe does, however, permit the use of a Shabbos timer for setting lights to go on and off. Even though he prefers to forbid the use of a Shabbos timer altogether, he permits using it for lights, because it was the accepted, common practice in Europe to have a non-Jew extinguish and re-kindle the lights in the homes of Jews at given hours. We do not have to be more stringent with regard to a Shabbos timer.
Other authorities differ with Rav Moshe's ruling.
(b) The CHAZON ISH (OC 38:2,3) permits setting a Shabbos clock to perform Melachah on Shabbos. SHEMIRAS SHABBOS K'HILCHASAH concludes that it is permitted as well.
RAV SHLOMO ZALMAN AUERBACH (MINCHAS SHLOMO) even permits changing -- on Shabbos -- the time that a Shabbos timer is set to perform a Melachah by turning the dial in such a way that one delays the action that the Shabbos clock would have caused, because doing so is not considered to be performing any Melachah.