Q&A from the Bais HaVaad Halacha Hotline

Time Travel

November 14, 2024

Q On Shabbos, may one adjust the pegs of a plug-in timer (a.k.a. Shabbos clock) to change its schedule?

A Adjusting the timer’s pegs does one of two things:

• It prolongs the machine’s current state, postponing the time it turns on or off.
• It hastens the change, causing it to turn on or off earlier.

The poskim view the former case more leniently than the latter, because the change is passive rather than active.

Following this, R’ Shlomo Zalman Auerbach (Minchas Shlomo 1:13) permits removing the pegs (or pushing them in, depending on the model) to cause the lights to stay on or off longer. In his view, the pegs are not muktzeh. According to R’ Moshe Feinstein (Y.D. 3:47), the pegs are muktzeh and may only be adjusted with a shinui.

Regarding making the timer switch on or off earlier, R’ Shlomo Zalman applies the principle of grama. He cites the halacha (O.C. 334:22) that one may place a barrier of water-laden ceramic vessels in the path of a fire so that when the fire reaches the vessels, they will crack open from the heat, and the water will douse the flames. Because the melacha of mechabeh is performed only indirectly, this is permitted. But the Rama says this is permitted only to prevent a significant financial loss.

Inserting pegs, explains R’ Shlomo Zalman, is akin to putting the water vessels in the fire’s path, because inserting the peg will cause a melacha to be done eventually. It is therefore forbidden except to prevent significant financial loss. For the needs of a sick person, or for a mitzvah, one may be lenient (ibid. and Shmiras Shabbos Kehilchasah 13:28).

Even when it is permitted, it is advisable to avoid adjusting a timer unless no other option is available, because some poskim consider it uvda dechol (a weekday activity), and because mistakes can easily be made (See Piskei Teshuvos 277:5).

In all cases, a non-Jew may be instructed to make the adjustment, because amirah lenachri is permitted in cases of grama (Piskei Teshuvos ibid.).