In a proceeding to vacate an arbitration award, the appeal is from a judgment of the Supreme Court, Kings County (Pino, J.), dated April 12, 1985, which granted the application.
Justice Niehoff has been substituted for the late Justice Gibbons (see, 22 NYCRR 670.2 [c]).
Ordered that the judgment is affirmed, with costs.
We agree with Special Term that the subject arbitration award cannot stand. One of the limited statutory (CPLR 7511) grounds to vacate such an award is that the arbitrator exceeded his power.
The collective bargaining agreement clause which provided for arbitration herein expressly limited the arbitrator’s power to "the interpretation and application of the provisions of this agreement or of any written working condition, rule or resolution”. Whether the agreement expressly limits the arbitrator’s power has been held to be a basic factor in determining whether an arbitrator has exceeded his power (Pavilion Cent. School Dist. v Pavilion Faculty Assn., 51 AD2d 119, 122-123, lv dismissed 40 NY2d 845, 42 NY2d 961), and an award may be vacated where an arbitrator has exceeded expressly delineated powers (see, Matter of Granite Worsted Mills [Cowen], 25 NY2d 451, 456-457). Despite the explicit limitation contained in the agreement, the arbitrator found a violation of the agreement based on his interpretation of it by considering past practices of the parties and without pointing to any specific provision alleged to have been violated by the petitioner.
While it is not irrational for an arbitrator to consider past practices (see, Matter of Manhattan & Bronx Surface Tr. Operating Auth. v Local 100, Transp. Workers Union, 84 AD2d 749, 750) to interpret provisions of the contract (Rochester City School Dist. v Rochester Teachers Assn., 41 NY2d 578, 583), he may not do so, as here, to the extent of bypassing express contract provisions and relying on these practices so as to make them an implied part of the contract. If the arbitrator does so, it will be concluded that he has exceeded his power by rewriting the contract and the award will be vacated (County of Ontario v Civil Serv. Employees Assn., 76 Misc 2d 365, 367-368, affd 46 AD2d 738; see also, Matter of Board of Educ. v *709North Babylon Teachers’ Org., 104 AD2d 594, 597). The arbitrator’s decision derived not from the contract, which granted petitioner broad discretionary powers to enact the change of schedule which prompted the appellant’s grievance, but, rather, apparently from his deliberate and intentional consideration of matters dehors the contract (see, Matter of Civil Serv. Employees Assn. v County of Steuben, 50 AD2d 421, 425). Furthermore, the fact that the arbitrator did not cite any provision or section of the agreement which was in fact violated may itself be determinative of the issue of whether he has exceeded his power (cf., Matter of Board of Educ. v North Babylon Teachers’ Org., supra, at 598). Niehoff, Weinstein and Kooper, JJ., concur.