At the request of a party the court may order witnesses excluded so that they cannot hear the testimony of other witnesses, and it may make the order of its own motion. This rule does not authorize exclusion of (1) a party who is a natural person, or (2) an officer or employee of a party that is not a natural person designated as its representative by its attorney, or (3) a person whose presence is shown by a party to be essential to the presentation of his cause,  or (4) a person whose presence is determined by the court to be in the interest of justice. (1983, c. 701, s. 1.)