(a) Where:
(i) three arbitrators are to be appointed;
(ii) the parties have not agreed on an appointment procedure; and
(iii) the Request for Arbitration names more than one Claimant;
the Claimants shall make a joint appointment of an arbitrator in their Request for Arbitration. The appointment of the second arbitrator and the presiding arbitrator shall, subject to paragraph (b) of this Article, take place in accordance with Article 17(b), (c) or (d), as the case may be.