Under Evid. Code section 703.5, an arbitrator’s declaration or live testimony is inadmissible except for extremely limited purposes such as to show bias or conduct constituting contempt or a crime.  Accord: Cobler v. Stanley, Barber, Southard, Brown & Associates (1990) 217 Cal.App.3d 518, 528.  This section applies to and limits the admissibility of party-nominated arbitrators or appraisers in three-arbitrator/appraiser proceedings in which only the umpire or third arbitrator (chosen by the other two) is truly neutral.

California Court of Appeal, Second District, Division Four (Manella, J.); February 27, 2018; 2018 WL 1062404.