CAISO board approves 50 MW large-load rules for its FERC filing

The California ISO's Board of Governors voted 5-0 on October 28, 2026 to approve the grid operator's answer to FERC's June order on large loads, per the board's motion record. The package defines a large load as an end user at a single site behind one or more points of interconnection to the CAISO-controlled grid with a peak of 50 MW or more, creates a curtailable interim service for loads that arrive before their network upgrades are finished, and has CAISO publish what those upgrades cost. The motion authorizes management to make the filings at FERC; the initiative page lists the filing for November 16.

FERC's June 18 order in docket EL26-71 found that the tariffs of CAISO and its participating transmission owners "appear to be unjust, unreasonable, or unduly discriminatory or preferential" for lacking large-load provisions, and told them to defend those tariffs or propose changes. FERC sent tailored orders that day to all six regional grid operators it regulates, per CAISO's board memo. The orders cover large loads such as data centers and manufacturing operations, per CAISO. "Our response to the FERC order to show cause will improve planning and operational awareness of new large loads on the system, prevent cost-shifting, encourage flexibility and expedite large load energization," CEO Elliot Mainzer said in CAISO's announcement.

What the board approved

The 50 MW line matches the threshold FERC floated, but CAISO's definition leaves out FERC's other suggested terms, including interconnection above 69 kV and the exclusion of co-location arrangements. The memo concedes the definition misses distribution-connected loads and transmission-connected loads under 50 MW, which CAISO will keep studying in planning. The same 50 MW floor appears in PJM's large-load registry, which FERC accepted on October 9, and in NERC's computational load standards, which add a 100 kV test. CAISO's draft final proposal is candid about the price of any number: "The CAISO recognizes that any arbitrary cutoff creates some incentive to avoid the load-peak threshold."

For developers, the speed piece is Flexible Interim Load Interconnection (FILI): curtailable, interim service that lets a large load connect before its network upgrades or interconnection facilities are complete. Under the revised draft tariff language posted October 26, CAISO, the transmission owner and the load sign an agreement before energization setting when the load can be curtailed, by what mechanism and by whom, and CAISO posts those agreements on its website. That could mean remedial action schemes, transmission-owner curtailment or a pre-set schedule, per the board presentation. The memo says CAISO will review out-of-cycle transmission additions for large loads monthly to fit FERC's 60-90 day window for the owners' load studies, and proposes hourly forecasts and telemetry from large loads plus protocols for disconnecting them remotely through the transmission owner when reliability requires it.

The October 26 language also exempts loads already in motion: CAISO will not treat a load as a Large Load if it is operational or has a complete request with its transmission owner before a date the draft still leaves in brackets, "[February 14, 2027/effective date]", unless it later modifies or increases itself into one or opts in.

A permanent flexible service did not make the cut. The memo puts it, along with interconnection of electrically proximate loads and generation, in a stakeholder initiative expected to begin policy development in early 2027. Constellation backed approval in a letter to the board dated October 28, but pointed to FERC's concern that CAISO's tariff may not provide service for flexible large loads "on both an interim and permanent basis" and said deferring the permanent option "would leave a central element of FERC's preliminary Section 206 concern unresolved."

Who pays for the wires

CAISO leaves most of the cost question to the utilities. The memo expects participating transmission owners to write deposit, financing and other cost allocation rules into their own tariffs, and says fair accounting will ensure that only each owner's revenue requirement net of what it receives from large loads sets the regional high-voltage transmission access charge (TAC), recovered across all loads and exports. CAISO's own part is transparency: the Transmission Plan will carry aggregate proposed and completed large-load additions by transmission zone and the planned network upgrades needed for large loads, with estimated costs. The October 26 revision struck a qualifier that had limited those upgrades to large loads "with executed interconnection agreements."

The state's ratepayer advocate and one of the utilities were not persuaded. In October 15 comments on the September 24 draft final proposal, the CPUC's Public Advocates Office wrote: "It is not reasonable for CAISO to assume that PTOs will develop sufficient proposals and exclude the appropriate costs from the revenue requirement." It warned that if transmission owners refund large loads' payments, the costs flow into revenue requirements "paid for by all TAC ratepayers." It also asked CAISO to stop using its concurrence process to approve costly upgrades for large-load interconnections, citing nearly $2 billion in network upgrades CAISO concurred with to interconnect 11 large loads in the 2025-2026 Transmission Plan and over $2.5 billion PG&E has proposed for 13 in the 2026-2027 cycle. Southern California Edison, itself a transmission owner, wrote that "Simply deferring the TOs to handle this without CAISO engagement is inconsistent with and does not satisfy the requirements of the OSC," and that CAISO "is the only entity in the position to study these costs and determine the amount attributable to a specific LL."

The memo names both and answers in one line: "Management believes the ISO has struck the right balance in terms of the division of responsibilities with the participating transmission owners."

PG&E and the Public Advocates Office both say the definition catches too few loads, for different reasons. PG&E wrote that it "will result in few, if any, large loads in the CAISO region meeting the definition" because it reached only end users whose own point of interconnection is the CAISO grid, unlike PJM's and NYISO's "behind one or more" wording. The October 26 language now says "behind one or more points of interconnection," and the memo says CAISO is still working with PG&E, the CPUC and others on consensus tariff language. The Public Advocates Office objected to the 50 MW floor: PG&E has submitted large loads that sit narrowly below the cutoff (e.g., 49 MW), and those sub-50 MW loads contribute to over $1 billion in interconnection and capacity upgrade costs, so it asked for no threshold or a 20 MW one.

Outlook

The board presentation lists section 205 tariff filings from both CAISO and the transmission owners for November 16, so how much protection ratepayers get will turn partly on the owners' filings. FERC's June order lets interested entities respond within 30 days of those filings, a second venue for the arguments the board heard. An unsettled PG&E definition dispute would likely join them. PJM faces the same November 16 date in its own proceeding (see our interconnection reference page) and now plans to put its ride-through rules for data centers into that filing.