FERC has accepted a 17-month delay to ISO-NE and the New England transmission owners’ (TOs’) implementation of Order 881 and Order 881-A compliance, pushing back the rollout of ambient-adjusted line ratings (AARs) in the region. The RTO and the TOs said the delay is needed to accommodate vendor and software development challenges (ER22-2357, ER25-410). 

FERC Order 881, issued in December 2021, requires transmission providers to adopt AARs, which provide more accurate real-time temperature information on transmission lines, for near-term transmission requests. The order is intended to free up transmission capacity, as existing static rates are based on worst-case temperature conditions. The order also requires operators to use seasonal line ratings for long-term transmission service. (See FERC Orders End to Static Transmission Line Ratings.) 

ISO-NE and the TO’s compliance with the order was to take effect in July 2025 but has been pushed to December 2026.  

“Considering the vendor delay in delivery of the software that is needed for ISO-NE and the [participating transmission owners] to implement Order No. 881, and the time to test and train after delivery of the software, it is highly unlikely that the filing parties will be able to implement the tariff rules as of July 12, 2025,” the groups wrote in their request to FERC.  

The organizations wrote that ISO-NE plans to complete “all initial integrated software testing by January 2026,” which would be followed by trainings, TO testing and procedure development prior to the rollout of AARs in “all required day-ahead and real-time processes.” 

No protests of the request were filed in the docket. FERC accepted the request in a brief order May 30, writing that “good cause exists to defer the effective dates to implement the requirements of Order Nos. 881 and 881-A in order to provide additional time to complete the development and deployment of necessary software updates.”