623. When Shofar is Not Blown Before Shabbos

Shabbos 5:20

The first tekiah is to be blown at plag hamincha (one and a quarter halachic hours before sunset) and the final tekiah close to sunset. Similarly, the shofar should be blown on Saturday night to notify the people that they are permitted to resume their business.

Shabbos 5:21

If Yom Kippur falls on Friday, the shofar is not blown; if it starts on Saturday night, the shofar is not blown and havdalah is not recited. [Note: Yom Kippur cannot fall on Friday or Sunday under our current fixed calendar but it could when the calendar was set based on the testimony of witnesses.] If a yom tov falls on Friday, the shofar is blown but havdalah is not recited. If a yom tov starts after Shabbos, the shofar is not blown but havdalah is recited.