Q: Dear Rabbi Simon,
You recently responded to a question regarding a power cut resulting in the total cooling off of the food. As your ruling of lenience was based on the fact that there had been no deliberate human input whatsoever (actually on Shabbos itself?), does this imply that the use of a time switch to achieve the same effect would therefore not be permitted?
A: Dear Moshe
Thank you for your question. My delay in replying is partly due to the need to research the matter anew. Of course the classic (pre-20th century) sources do not deal with electricity, and the case of benefiting from the actions of a gentile on Shabbos – which is discussed in the Talmud and the Codes – is not necessarily the same as setting a time switch (so-called “Shabbos clock”).
At any rate, the answer is that it is indeed problematic to arrange ab initio (le-chatchilah) for your urn, for example, to turn off at night, and then to turn on again before lunch, boiling the water anew at that time. The reason for this is that you would effectively be removing the hot water from the source of heat, and then restoring it hours later. The same would apply to cholent (although I would add that such a strategy may be unwise from a bacteriological point of view.) Nevertheless, ex post facto (be-di’eved) you would still be allowed to consume your hot drink. However, if you do not need your electric hot plate overnight, but only (to re-heat in a permissible manner solid food which has already been cooked) during the day, you would be able to “save the planet” and your energy bill by setting a time switch to turn it off after dinner and on again before lunch.
I hope this is helpful. As they used to say in America, “power to the people”.