(a) The charges to property accounts, operating expenses, or other accounts for services and expenses of employees engaged in both construction and operation or in more than one class of operations, shall be based upon the actual time engaged in each service, or in case that is impracticable, upon percentages based on study of the time actually engaged during a representative period.

(b) The pay and expenses of general officers of the municipal electric utility and of general municipal officers and employees shall be included in the accounts of the municipal electric utility to the extent that they are actually engaged in such work based upon the actual time so engaged, and shall be charged to the actual work on which they are engaged, to the particular operations over which they have direct supervision, or to the appropriate accounts provided in the administrative and general group in operating expenses.

(c) Salaries of officers or employees and incidental expenses which can be distributed equitably upon a predetermined basis may be distributed through clearing accounts.