(2) In the following cases the commission may allow in rates, directly or indirectly, amounts on the utility’s books of account which the commission finds represent undepreciated investment in a utility plant, including that which has been retired from service:
(a) When the retirement is due to ordinary wear and tear, casualties, acts of God, acts of governmental authority; or
(b) When the commission finds that the retirement is in the public interest. [1987 c.447 §11; 1989 c.956 §3]