The court may impanel more than 12 jurors. If more than the number of jurors required to decide the case are left on the jury before deliberations are to begin, the names of the jurors must be placed in a container and names drawn from it to reduce the number of jurors to the number required to decide the case. The court may retain the alternate jurors during deliberations. If the court does so, it shall instruct the alternate jurors not to discuss the case with any other person until the jury completes its deliberations and is discharged. If an alternate juror replaces a juror after the jury retires to consider its verdict, the court shall instruct the jury to begin its deliberations anew.