(a) If the utility is engaged in more than one utility service, such as steam and electric or gas, and any of its utility plant is used in common for several utility services or for other purposes to such an extent and in such manner that it is impracticable to segregate it by utility services currently in the accounts, or if general equipment is of such a nature that even though it is used exclusively for one class of utility service or is associated with one process or function within a department, it is likely to be used simultaneously by more than one department or is subject to transfer between departments, such property may be designated and classified as “Common Utility Plant”. (See accounts 109.1 to 109.6 for common utility plant.)

(b) Utility plant designated as common utility plant shall be classified according to the detailed utility plant accounts appropriate for the property. Provisions in this system of accounts applicable to steam plant accounts shall extend also to the accounts for common utility plant.

(c) The utility shall be prepared to show at any time and to report to the commission annually, or more frequently if required, and by utility plant accounts (301 to 390), the following: (1) the book cost of common utility plant, (2) the allocation of such cost to the respective departments using the common utility plant, and (3) the basis of the allocation.

(d) The expenses of operation, maintenance, depreciation and taxes of common utility plant shall be recorded in the accounts prescribed herein, but designated as common, and the allocation thereof to the departments using the common utility plant shall be supported in the same manner as the allocation of the cost of such property.