(a) For each class for which the salary range is designated by the Department as trade rate, the Department shall determine and promulgate, as often as conditions require, a trade rate range that meets the conditions below.

(b) In establishing a trade rate range, the Department shall confer with and take into account the findings of state, county, municipal, and other official public bodies engaged in determining the prevailing rate in connection with the awarding of contracts for public works and shall consider such other sources of pertinent information as may be available.

(c) Whenever the trade rate range for a class is revised, the salary of each incumbent in a position to which the revised range applies shall be adjusted to the step in the revised range that corresponds to the step received in the previous range; and such salary adjustment shall not affect the date of eligibility for a merit salary adjustment.

(d) The salary that an employee shall receive upon appointment to a trade rate apprenticeship class shall conform to the wage rate provisions found to be prevailing for the apprenticeship.