ISO Path 15/26

Good Morning,

Several clients have asked about our “missing” Path 15 and 26 data in our transmission reports. Apparently, the ISO, in its infinite wisdom, has decided to drop reporting for both lines. Why not, they’re only the two most important lines in WECC. A further reason why PJM needs to take over the WECC.

I received this email back from ISO:

There will be a call on Thursday where the ISO will explain their thinking.  Here is the info on that call:

Market Notice
November 12, 2018


Mark Your Calendar


Market Rules and Design

TTC and ATC for Path 15 and Path 26 No Longer Available, Call11/15/2018


The California ISO will hold a public stakeholder call on Nov. 15, 2018, to address questions received related to the termination of calculating and posting of the Total Transfer Capability (TTC) and the Available Transfer Capability (ATC) within the OASIS application for Path 15 and Path 26. The ISO published a market notice on Oct. 31, 2018, announcing that the ISO would no longer calculate and post TTC and ATC.


In May 2015, the ISO stopped enforcing Path 15 and Path 26 branch groups and started to enforce the reliability constraints through the use of nomogram constraints. The OASIS system continued to post the available transfer capability for these paths, due to a posting requirement defined in Appendix L of the ISO tariff. The ISO filed for a tariff language clarification through a tariff clarifications filing, which was approved and effective November 1. Accordingly, on November 1, the ISO stopped publishing the TTC and ATC values. The ISO continues to manage the reliability constraints through nomograms, and continues to make available the constraints definitions and enforcements similar to other transmission constraints.


The call will be recorded and the audio file posted on the initiative webpage for a limited time. The recording is for informational and convenience purposes only, and any related transcriptions should not be reprinted without the ISO’s permission.


Meeting Details

Date: November 15, 2018

Time: 10 a.m. – 11 a.m. PT

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Participation Information

Call: 1-877-369-5230, Access code: 0157846##

Technical support: call the AT&T Help Desk at 1-888-796-6118



Dede Subakti at [email protected] or ISO Customer Service at 916-608-7320