(1) How served. Service of papers may be made personally or by first-class mail, registered or certified mail, or telegraph, or by leaving a copy at the principal office or place of business of the person to be served.

(2) Who serves. The commission shall cause to be served all orders, notices and other papers issued by it, together with any other papers which it is required by law to serve. Every other paper shall be caused to be served by the party filing it.

(3) Upon whom served. All papers served by the commission or any party shall be served at the time of filing upon all counsel of record and upon parties not represented by counsel or upon their agents designated by them or by law. Any counsel entering an appearance subsequent to the initiation of the proceeding shall notify all other counsel then of record and all parties not represented by counsel of such fact.

(4) Service on commission. In a matter pending before the commission or an administrative law judge in which the commission is being represented by the attorney general or a staff person other than the clerk, service on the commission shall be made by serving the attorney or staff person who is acting for the commission. In such matters, filing a paper with the clerk is not service on the commission. Service of a petition for judicial review under the Administrative Procedure Act, chapter 34.05 RCW, is governed by RCW 34.05.542 and not by these rules.

(5) Service by mail. If service is made by mail, the papers shall be deposited in the post office addressed to the person on whom they are being served, with the postage prepaid. Unless earlier receipt is shown, service by mail shall be deemed complete upon the third day following the day upon which the papers are placed in the mail, unless the third day falls on a Saturday, Sunday or legal holiday, in which event service shall be deemed complete on the first day other than a Saturday, Sunday or legal holiday following the third day.

(6) Filing, generally. Papers required to be filed with the commission shall be deemed filed on actual receipt at the commission's Olympia or Seattle office, or other place previously specified, accompanied by proof of service on any parties required to be served.

(7) Filing with administrative law judge. Papers required to be filed with an administrative law judge shall be filed with the clerk, 402 Evergreen Plaza, Mailstop FJ-41, Olympia, WA 98504, unless otherwise directed. They must be accompanied by proof of service on all parties required to be served. The original of each paper shall be filed, accompanied by two copies.