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Moving A shabbos clock on shabbos


We have central air conditioning on a shabbos clock. Is one allowed to move the pieces on the clock on shabbos so that the air condition will continue going longer?


There is much discussion among contemporary poskim if one is allowed to move the trippers of a shabbos clock. The poskim agree that it is prohibited to move the trippers so that the lights will go on or off earlier. For example, if the lights are on and are due to turn off in an hour, one may not move the trippers so that the lights go off in half an hour. Or vise versa, if the lights are off and should go on in an hour, to move the trippers so that they will go on in half an hour. This is because this is a גרם כיבוי or גרם הבערה – causing a fire to turn on or off1.

There is however controversy whether one may extend the present situation that the shabbos clock is on or not. For example if the lights are presently on, to move the trippers so that it stays on for longer, or, if the lights are off, to move the trippers so that the lights stay off for longer.

Most poskim2 prohibit moving the trippers even to extend the present situation, for a variety of reason. Some say because it isn’t considered causing the electric to turn on, rather as if it is directly being turned on. Others say because the trippers are muktza, or because it is עובדא דחול weekday-like. Another reason given is because it is very easy to make a mistake and be מחלל שבת.

On the other hand R. S. Z. Auerbach zt”l permitted moving the trippers so that the existing state of the lights remain longer, such as making the l which presently on to stay on longer, or off to stay off longer 3.

It must be noted that even according to the opinion that permits moving the trippers, it is permitted only if one does not have to stop the functioning of the shabbos clock. However if the functioning of the clock has to get stopped such as if the dial has to be removed in order to change the settings, then it is forbidden.

Aside from the fact that most poskim do not permit moving the trippers on shabbos, it is also a risky thing to do. This is because often people get mixed up between extending the present situation to shortening it, which everyone agrees that it is not permitted, and secondly very often, while the person is attempting to move a tripper, it causes the dial to move which turns the lights off or on, or even by merely turning it, that in itself is causing the current status to become shorter. Something which everyone agrees is  not permitted.


[1]Shmiras Shabbo s kHIlchoso 13-28,

  1. Livushe Mordichai 3-O:CH 25, Chelkas Yackov 1-55, Igros Moshe O:CH 4-91(5), Y:D 3-43(4), Tzitz Eliezer 1-20, 6-5, Shalmei Yehudah chap.2-6 in the name of R’ Eliyashev zt”l, Minchas Yitzchok 1-58, Be’er Moshe 6 Kuntris Elctric-36, Oz Nidbiru 3-25, Btzel Hachochma 2-32, Yaskil Avdei 4-17, Yisodei Yishurun –Mechabeh pg. 157.

3 MinchasShlomo 1-14, ShmirasShaboos Khilchoso ibid.Yabia Omer3-17-18.

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