(4) If the appointment procedure in sub- section (3) applies and-
(a) a party fails to appoint an arbitrator within thirty days from the receipt of a request to do so from the other party; or
(b) the two appointed arbitrators fail to agree on the third arbitrator within thirty days from the date of their appointment, the appointment shall be made upon request of a party, by the chief justice or any person or institution designated by him.