[Avodah] sparks on shabbat

[Eli Turkel]

from
http://koltorah.org/halachah/prohibition-turning-incandescent-bulb-shabbat-and-yom-tov-part-2-2

Approach #4 – Sparks
Both Rav David Zvi Hoffman and the Chazon Ish note that it is
prohibited to complete circuits due to the sparks that are created
when one completes a circuit. They argue that the sparks generated
when completing an electric circuit fall into the rabbinic prohibition
to create sparks from wood or stones (Mishnah Beitzah 4:7).
Rav Shlomo Zalman (Teshuvot Minchat Shlomo 1: pp. 86-87) strongly
questions this assumption. He notes that not only does one not intend
to create these sparks, but also one does not want them at all since
they wear out the points of contact in a circuit. He also argues that
this is considered an unusual manner (KeLeAchar Yad) to create sparks
since one never completes a circuit with the intention of creating
sparks. Accordingly, Rav Auerbach argues that there should be no
Halachic problem associated with the creation of such sparks.
He draws an analogy to a ruling of the Dagul MeiRevavah (O.C. 340:3)
where he permits cutting a cake with letters written on it. This
permission is based on the combination of the fact that erasing when
not done for the purpose of writing is only a rabbinic prohibition, he
has no intention of erasing the letters, it is a destructive act
(Mekalkeil), and this is a KeLeAchar Yad manner of erasing.
Accordingly, since the creation of sparks in general is only a
rabbinic prohibition, and one does not intend to create sparks when
completing an electric circuit, it is an unusual manner to create
sparks, and it damages the circuit, the creation of sparks when
completing an electric circuit does not constitute a prohibited act on
Shabbat.
We should note, however, that Rama (ad. loc.) does prohibit breaking a
cake with letters on it. Although the Shaarei Teshuvah (340:1) fully
accepts the ruling of the Dagul MeiRevavah and the Aruch HaShulchan
(O.C. 340:23) essentially supports it, the Mishnah Berurah (340:16)
does not fully accept this lenient ruling. Indeed, common practice is
to avoid cutting the letters on a cake on Shabbat in harmony with the
ruling of Rama.
On the other hand, the fact that Halachah attaches no significance to
something that is not visible to the "naked eye" (see Aruch HaShulchan
Yoreh Deah 84:36 and Teshuvot Igrot Moshe Y.D. 3:120:5) is another
consideration to discount these sparks. The Encyclopedia Talmudit
(18:734) states that turning on appliances that operate on a
relatively low voltage does not make visible sparks. Moreover, the
production of sparks depends to a great extent on humidity. Thus,
since it is not inevitable (Pesik Reisha) that these sparks will be
produced, it remains an unintended action (Davar ShEino Mitkavein),
which is permitted on Shabbat.

-- 
Eli Turkel