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December 18, 2020


Forward to Operating Department


Notification of Revised ISO Operating Procedure 4120 and Retired ISO Operating Procedure 4120C


The California ISO has revised the operating procedures referenced below.


4120 Gas Transmission Pipeline System Limitations or Outages, version 7.0, effective Dec. 18, 2020.

  • Periodic Review: Major update, incorporating content from 4120C and rewriting Sections 3.2 - 3.4 to Separate Gas Nomogram procedures in Section 3.2, clarify other gas limitation procedures using fuel insufficiency Nature of Work (NoW) in Section 3.3 and separate gas curtailment steps to clarify use of ambient not due to temp NoW card in Section 3.4.
  • Section 3.5: Minor updates to content included from 4120C.
  • Section 3.6: Market Notification (Market Notification System (MNS) and Automated Dispatch System (ADS) Scripts, added “pursuant to Operating Procedure 4120” and updated content from 4120C.
  • Updated procedure title.
  • Section 5: Minor update for clarification.
  • Minor format and grammar updates.
  • Added document control statement in footer.
  • Removed version history prior to five-years.
  • Removed reference of 4120C, as it is retiring with this publish.


4120C SoCalGas Service Area Limitations or Outages, version 2.3, effective Dec. 18, 2020.

Retired - relevant sections included within main 4120 procedure.


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California Independent System Operator | P.O. Box 639014 | Folsom, CA 95630 | United States