Five sessions after Wednesday’s close, on Monday July 20, the six regional grid operators covered by the Section 206 show cause orders FERC issued June 18 file the generation adequacy reports that anchor the substantive tariff response due August 17. The generation adequacy filings are not themselves the tariff response. They are the analytical basis each ISO will use to argue either that its existing rules remain just and reasonable in light of large load growth, or that specific tariff reforms are necessary. The August 17 deadline is 33 days from Wednesday. The intervention window on the six dockets closed July 9, which means the participant list on the tariff review is now fixed.
The June 18 orders were the Commission’s answer to a question the PJM co-location proceeding surfaced but did not resolve for the rest of the country. The December 18, 2025 order in the PJM Section 206 proceeding gave PJM a framework built around two new transmission products, Firm Contract Demand and Non-Firm Contract Demand, that let a co-located large load contract for a defined block of grid backstop without taking full Network Integration Transmission Service. That framework covers PJM. It does not cover MISO, SPP, CAISO, ISO-NE, or NYISO. FERC’s June 18 orders extend the same regulatory pressure to every other RTO and ISO, on a compressed calendar and against a menu of five specific reform categories.
What the June 18 orders actually require
Each of the six show cause orders directs the RTO or ISO, together with its transmission owners, to demonstrate within 60 days that its existing tariff remains just and reasonable in light of large load integration facts, or to file tariff changes that address the categories the Commission identified. Both response modes land August 17. The Commission signaled in the orders that the burden of persuasion is now on the ISO to defend the status quo, not on complainants to prove specific harm. That is a shift in the analytical posture. Under the standard Section 206 review, a challenger would need to show that the existing rate is unjust and unreasonable and that a specific alternative is just and reasonable. Under the show cause posture the Commission has taken here, the ISO carries the initial burden.
The five categories FERC named in the June 18 orders read as a menu of the answers the Commission expects.
Efficient transmission service application and study processes for large loads. The category maps to the queue delay problem. A large load applying for transmission service today runs through the same study process as a smaller load with substantially different scale characteristics. The Commission is asking each ISO to justify why that treatment remains reasonable or to propose a differentiated study track for large loads above a defined threshold.
Cost shift prevention and transmission cost transparency. The category maps to the ratepayer protection question. Large loads that take non-standard transmission service, whether through co-location or through direct contract structures, can shift transmission and ancillary service costs onto other ratepayers if the pricing is not properly designed. The Commission is asking each ISO to show that its existing cost allocation rules capture the actual cost causation, or to propose revised rules that do.
Accommodating colocation agreements and behind-the-meter generation. The category maps most directly to the PJM co-location framework. The Commission is signaling that every RTO and ISO should have a defined tariff position on co-located load and behind-the-meter generation, rather than handling each case as a nonstandard filing. This is where the equivalent of PJM’s Firm Contract Demand and Non-Firm Contract Demand products would live in each of the other five markets.
New transmission services for flexible large loads. The category maps to the interruptibility question. A large load that can be curtailed under defined conditions imposes a smaller reliability burden on the system than a firm load of the same nameplate size. The Commission is asking each ISO to consider a differentiated transmission product for flexible or interruptible large loads, priced against the reduced reliability burden.
A process to study generating facilities that serve electrically proximate large loads and colocated loads. The category maps to the generator-load pairing question. When a specific generator is dedicated in whole or in part to a specific large load, the generator’s contribution to system reliability shifts. The Commission is asking each ISO to define how it will study that shift, both for the initial pairing and for the ongoing operational treatment.
What the July 20 filings will contain
The generation adequacy reports due Monday are the analytical foundation, not the tariff response. Each report is expected to cover the current and projected load and generation balance in the ISO footprint, with specific attention to the large load additions in the interconnection queue and the generation additions expected to serve them. The reports will disclose the assumptions each ISO is using about data center load ramp rates, hyperscaler co-location intentions, and behind-the-meter generation commitments. Those assumptions matter for the tariff response, because a report that projects a modest large load ramp is compatible with an ISO defending its existing rules, and a report that projects a rapid large load ramp effectively forecloses that defense.
The specific input to watch in each report is the treatment of the load requests that have been filed but not yet studied. PJM has the most visible backlog, with published queue data showing tens of gigawatts of new large load requests in the past 18 months. MISO has a smaller but rapidly growing backlog concentrated in the Ohio, Indiana, and Iowa footprints. SPP has a smaller backlog concentrated in Oklahoma and Texas panhandle data center sites. ERCOT is not part of the six dockets because ERCOT is not FERC-jurisdictional, though the Public Utility Commission of Texas has parallel proceedings. CAISO’s large load pipeline is smaller in nameplate but concentrated in a footprint with severe transmission constraints. ISO-NE and NYISO have the smallest large load pipelines of the six, but also the highest existing capacity prices and the most constrained transmission systems.
A generation adequacy report that projects modest large load additions inside the existing reserve margin gives the ISO a defensible basis to argue the existing tariff remains just and reasonable. A report that projects large load additions materially exceeding the existing generation queue creates the analytical basis for a tariff response that names specific reforms. The Commission will read the July 20 filings against the August 17 tariff responses as a paired submission.
Where the ISOs are likely to land
PJM is the least uncertain. PJM already has a co-location tariff framework in development under the December 2025 order, with the Firm Contract Demand and Non-Firm Contract Demand products defined and the specific tariff language filed in stages through the first half of 2026. The August 17 filing from PJM will most likely present the co-location framework as substantially responsive to the June 18 order, with targeted supplements addressing the categories that the December 2025 order did not fully cover. Those supplements are most likely to concentrate on the efficient study process category and the flexible large load transmission service category.
MISO and SPP are the highest-uncertainty responses. Both have signaled through 2026 stakeholder processes that they intend to develop co-location frameworks, but neither has an existing filing on the record. Both have to build a substantive tariff response inside a 60-day window from a starting point that lacks a definitional structure. Both will most likely file a proposed framework that borrows the categorical structure from PJM’s Firm and Non-Firm Contract Demand products, adapted to their own market design and cost allocation rules. Whether either files a complete framework or a phased proposal with follow-on filings dated to Q4 2026 is the specific question to watch. A phased proposal on August 17 signals a market that is not ready to price co-location commitments through the end of the year.
CAISO has the most distinctive market design of the six, with the fifteen-minute market and the day-ahead market for both energy and ancillary services structured differently from the eastern RTOs. CAISO will likely propose a framework that fits its market design rather than transplanting the PJM categories directly. The California PUC will play a larger role in the CAISO response than the state commissions play in the eastern responses, because California retail load falls under CAISO in the CAISO balancing authority area but state PUC jurisdiction remains substantial on retail rate and generation siting issues.
ISO-NE and NYISO are the smallest large load pipelines but also carry specific characteristics that shape the response. ISO-NE operates the Forward Capacity Market, which prices capacity commitments three years forward, and any tariff change to accommodate large loads has to be compatible with the FCM auction structure. NYISO’s Installed Capacity market runs on a shorter horizon but has similar structural interactions. Both responses will most likely define co-location and behind-the-meter treatment against the specific auction mechanics rather than as standalone tariff products.
The August 17 to September window
The tariff responses due August 17 open a review window that FERC has historically resolved in two to four months for a proceeding of this complexity, which puts the operative resolution date in the Q4 2026 to Q1 2027 window. Any specific filing that proposes major tariff reforms will draw complaints from state PUCs, ratepayer advocates, and industrial customer groups, all of which had to intervene by July 9 to be full participants in the review.
The developer-side calendar reads against the review window. A hyperscaler evaluating a specific site in a non-PJM footprint has to decide during Q4 2026 and Q1 2027 whether to commit to a project on the basis of an interim tariff framework, a proposed framework awaiting FERC approval, or the existing rules that the show cause proceeding is challenging. That decision will move meaningful hyperscaler capital allocation across the six ISO footprints during the review window, with the specific direction of movement depending on which ISOs file the most defensible frameworks and which draw the most contested reviews.
The tax equity primary market and the transferability book are secondary readers of the same proceeding. Solar and storage projects sited to serve co-located data centers, whether directly through a corporate PPA or indirectly through the ISO capacity mechanism, price against the visibility on the co-location rules. A resolved tariff framework in each of the six ISOs by early 2027 supports a tighter primary spread on paper tied to data center offtake. A prolonged review with contested framework filings widens that spread.
What to watch Monday
Three specific inputs on the July 20 filings frame the August 17 response.
The projected large load additions inside each ISO’s five-year planning horizon, both in nameplate and in load factor terms. The specific number that matters is the ratio of projected large load additions to projected non-large-load additions. A ratio above 0.5 is the analytical threshold at which the ISO will find it difficult to defend the existing tariff as still just and reasonable.
The generation additions committed to serve the projected large load, and specifically the fraction of those additions structured as co-located or behind-the-meter arrangements versus network-connected generation. A high co-location fraction argues for a specific tariff product to price the arrangement. A high network fraction argues for a specific study process reform.
The reserve margin implication of the projected large load additions against the projected generation additions, including the treatment of nuclear license renewals, gas peaker additions, and battery storage in the reserve calculation. A projected reserve margin decline below the ISO’s target level in the five-year horizon creates specific pressure on the tariff response, and specifically on the flexible large load transmission service category.
By close of business Monday the six filings will define the analytical space for the August 17 tariff responses. By August 17 the specific tariff proposals will define the FERC review that runs into Q4 2026. By early 2027 the co-location rules for every FERC-jurisdictional footprint outside PJM will be set.
Sources
- Federal Energy Regulatory Commission, “FERC Launches Aggressive Targeted Action to Speed Large Load Integration,” news release, June 19, 2026, ferc.gov/news-events/news/ferc-launches-aggressive-targeted-action-speed-large-load-integration.
- McGuireWoods LLP, “FERC Issues Section 206 Show Cause Orders Directing All Six RTOs/ISOs to Justify or Reform Large Load Integration Rules,” client alert, June 2026.
- White & Case LLP, “FERC orders grid operators to promptly revise or justify interconnection rules for data centers and large loads,” insight alert, June 2026.
- Day Pitney LLP, “FERC Issues Show Cause Orders to Six RTOs/ISOs on Large Load Integration,” client alert, June 2026.
- Duane Morris LLP, “FERC Acts to Advance Data Center and Large Load Integration in Six RTO Regions,” client alert, June 2026.
- Bracewell LLP, “FERC Issues Show Cause Order on Large Load Interconnection Reforms to Support Data Centers and Advanced Manufacturing,” client alert, June 2026.
- Vinson & Elkins LLP, “FERC Institutes Six Simultaneous Section 206 Proceedings Targeting Large Load Interconnection Across All RTO/ISO Markets,” insight, June 2026.
- Federal Energy Regulatory Commission, Order on Show Cause Proceeding (PJM co-location), Docket EL25-49-000, issued December 18, 2025.