The incumbents of permanent positions who have held such positions for a period of at least six months continuously next preceding the time that a civil service system is first adopted shall be continued in their positions as if appointed thereto after examination and certification from a list of eligibles, and shall be governed thereafter by this division and the rules and regulations adopted pursuant thereto but shall not be subject to the six months' probation period.
Ca. Pub. Util. Code § 12131