Question: Why do some Jews not use electricity on the Sabbath?
Answer: The Bible says one should refrain from work on the Sabbath, and the Bible includes the kindling of fire as work (Exodus 35:3).
Observant Jews (primarily orthodox Jews) consider electricity to be a form of fire. These Jews do not turn on lights, ovens, televisions, radios and other electrical appliances on the Sabbath. Instead, prior to the start of the Sabbath, they often plug their electrical appliances into special "Shabbat clocks" which turn the lights, air conditioners, ovens, ... on and off at pre-set times.
Some authorities believe that electricity is not truly fire. However, they still believe in banning the use of electricity on the Sabbath as a way to prevent Jews from violating the Sabbath by doing work that can stem from the use of electricity.