3. In any case where customer deposits are authorized by this section,
a utility corporation or municipality may require a customer or
applicant for service to deposit a reasonable sum of money according to
the estimated quantity of such services necessary to supply the customer
or applicant for service for two months, to secure payment for such
services actually rendered, or for the rental of fixtures, instruments
and facilities actually supplied. Every such utility corporation and
municipality shall allow to every such customer or applicant for service
interest on the sum deposited at a rate per annum to be prescribed from
time to time and at least annually by the commission in light of current
economic conditions and current charges paid for moneys borrowed by such
utility, taking into account the expenses incurred by such utility in
obtaining, handling, returning or crediting the sum deposited. Such
interest shall be paid upon the return of the deposit, provided however,
that whenever such deposit has been held for a period of one year, the
interest shall be credited to the customer or applicant for service on
the first billing for utility service rendered after the end of such
period. If a customer or applicant for service is not delinquent in the
payment of any billing during such one year period, the deposit shall be
refunded promptly at the end thereof, without prejudice to the utility's
or municipality's right to require a deposit thereafter in the event of
a delinquency. All utility corporations and municipalities shall exempt
from deposit requirements any customer or applicant for service who is
sixty-two years of age or older, unless the customer or applicant for
service is a bad credit risk according to standards set by the
commission.