(a) If the utility desires to charge the appropriate accounts in any of its steam operations with the cost of steam used from its own supply, the credit therefor shall not be made to operating revenue accounts, but to account 806, Duplicate Miscellaneous Charges—Credit.

(b) Steam supplied by the utility from its own supply to other departments shall be accounted for in the following manner: If the steam is supplied under a definite arrangement whereby the actual costs are allocated between or among the departments using the steam, the credit in the accounts of the steam department shall be made to account 712, Steam Transferred—Credit, except that the amount of any return or interest, and the amount of depreciation and taxes charged against the other departments shall be credited to account 611, Interdepartmental Rents. If the charges are at tariff or other specified rates for the steam supplied, then the entire amount charged shall be credited to account 607, Interdepartmental Sales.