N.Y. Comp. Codes R. & Regs. tit. 16, § 197.16 – Joint expenses.

(a) In accounting for operating expenses incurred under arrangements between the municipal electric utility and others for joint use of facilities, the creditor in the first instance shall charge the entire expense to the appropriate accounts or to a clearing account. The portions borne by the debtor shall be credited by the creditor to the accounts previously charged therefor and charged by the debtor to the same accounts to which they would be charged if incurred directly to the debtor.
(b) Any allowance for profit or return and taxes on property used under the arrangement shall be credited by the creditor to account 621, Rent from Electric Property and charged by the debtor to the appropriate rent expense account.
(c) Bills covering charges by another party or by another department of the operating municipality under joint arrangements shall be so rendered or analyzed as to make possible allocation of the several elements thereof to the appropriate accounts.
(d) Operating expenses incurred for facilities operated by the operating municipality and used jointly by the municipal electric utility and any other department of the operating municipality shall be treated so that there will be available the details of the charges and the basis of the distribution to each department.
(e) Complete details or copies of contracts or agreements covering joint operations shall be filed with the commission. Such data shall include a statement outlining the reasons for the basis of allocation used.
Note:
When production operations are conducted under joint arrangements, the statistics for electricity produced shall be reported in a consistent manner so that each participant will report its share of the quantity of electricity produced.