Ohio Revised Code Title XLIX. Public Utilities § 4903.221

(1) Any specific deadline established by order of the commission for purposes of a particular proceeding; or, if no such deadline is established;

(2) Five days prior to the scheduled date of hearing.

The public utilities commission may, in its discretion, grant motions to intervene which are filed after the deadlines set forth in divisions (A)(1) and (2) of this section for good cause shown.

(1) The nature and extent of the prospective intervenor's interest;

(2) The legal position advanced by the prospective intervenor and its probable relation to the merits of the case;

(3) Whether the intervention by the prospective intervenor will unduly prolong or delay the proceedings;

(4) Whether the prospective intervenor will significantly contribute to full development and equitable resolution of the factual issues.