Interested director prohibition bars participation or voting in conflicted board decisions; breach attracts penalty under Companies Law. Section 300 bars an interested director from discussing, voting on, or being counted in the quorum for any contract or arrangement in which they are directly or indirectly interested; any such vote is void. The section lists exceptions-certain private companies, indemnity contracts for sureties, limited interests in public or subsidiary companies, and cases subject to Central Government notification-and prescribes a penalty for knowing contraventions.