FERC RM26-4 and the New Interconnection Rules Every Data Center Developer Must Understand#
FERC issued Section 206 show-cause orders to all six jurisdictional RTOs and ISOs on June 18, 2026, giving each region and its transmission owners 60 days to justify why existing tariffs remain just and reasonable without large-load-specific provisions — or file reforms. Each region filed a 30-day informational report in July 2026, and show-cause responses were due August 17, 2026, though a region intending to file its own reforms under Section 205 could request a stay instead. Either way the clock has run: the regional rules governing data center interconnection are being written now, not proposed for a future cycle.
Behind the show-cause package sits Docket RM26-4-000, FERC's national proceeding on interconnecting large loads to the interstate transmission system. The practical consequence for developers, EPCs, and lenders: the study process, the operating obligations, and the equipment scope attached to a 200 MW campus in 2026 are not the ones your 2023 pro forma assumed.
Key Takeaways
- RM26-4 is an ANOPR, not a NOPR. It is an early-stage proceeding gathering input before FERC decides whether to propose specific rules. It binds no one today, and it defines large load as demand greater than 20 MW.
- The binding instruments are regional. SPP's accepted HILL tariffs and FERC's December 18, 2025 order finding PJM's tariff unjust and unreasonable for co-located load are what governs a project right now.
- Conditional service carries hardware obligations. SPP's Conditional High Impact Large Load Service, accepted June 5, 2026, requires real-time telemetry and remote capability for SPP to disconnect the load from the transmission system.
- MISO reports large-load projects seeking connection in 18 to 36 months, against a framework goal of 120-day MISO approval once studies are complete and agreements are signed.
- Underwrite generation assessment and load-shed controls as line items, not contingencies. Both are now part of the interconnection record in SPP, and the show-cause responses will determine where else.
What RM26-4 Actually Is — and What It Isn't#
RM26-4 is an Advance Notice of Proposed Rulemaking. That distinction is not pedantry. An ANOPR is an early step in the rulemaking process that lets FERC gather input before deciding whether to propose specific regulatory changes — it precedes a Notice of Proposed Rulemaking, which itself precedes a final rule. Treating RM26-4 as an enforceable standard, or even as a formal proposal, is the most common modeling error in current data center pro formas.
The docket originated with a Department of Energy Section 403 directive in October 2025. It defines large load as electricity demand greater than 20 MW, which is the number most developers actually need from this proceeding — and the reason a 200 MW campus is squarely inside its scope while a 15 MW edge facility is not.
What FERC delivered in June 2026 was not a NOPR. It was the six show-cause orders, organized around five reform categories: application and study process efficiency, cost-shifting prevention and transmission-cost transparency, co-location and behind-the-meter generation, new transmission services for flexible large loads, and processes to study generation serving electrically proximate or co-located large loads. Four of those five have direct equipment consequences. RM26-4 itself remains open, with FERC signaling it may later address non-RTO utilities through the generic docket.
One point that materially changes project risk: FERC stated the show-cause orders are not intended to disrupt agreements large loads have already negotiated or are in the process of negotiating, and directed that any tariff revisions allow reasonable time to finalize commercial agreements nearing completion. If your interconnection agreement is signed or near-final, that language is the first thing your counsel should read.
ISO/RTO Large-Load Actions and Procedural Status#
| ISO/RTO | Docket | Instrument | Status | What it means for a data center |
|---|---|---|---|---|
| SPP | ER26-247-000 | HILL and HILLGA tariff revisions | Accepted January 14, 2026; effective January 15, 2026, subject to condition | Large-load study track plus a generation assessment where load brings its own new generation |
| SPP | ER26-1323 | Conditional High Impact Large Load Service | Accepted June 5, 2026 | Real-time telemetry; SPP remote capability to disconnect the load |
| PJM | EL25-49-000 | Section 206 show-cause on co-location | Instituted February 20, 2025 | Rates, terms, and conditions for co-located large loads |
| PJM | December 18, 2025 order | Tariff finding and directive | Tariff found unjust and unreasonable | Transparent co-location rules and new transmission service options |
| MISO | EL26-70-000 | Section 206 show-cause | Issued June 18, 2026; response due August 17, 2026 | Study procedures, cost transparency, co-location terms, flexible service |
| PJM, SPP, NYISO, CAISO, ISO-NE | EL26-67, -68, -69, -71, -72 | Section 206 show-cause | Issued June 18, 2026; responses due August 17, 2026 | Justify tariff without large-load provisions, or file reforms |
| MISO | Large Load Additions | Regional process | Active process revisions underway — not an accepted tariff equivalent to SPP's | 120-day approval goal once studies complete and agreements signed |
| All | RM26-4-000 | ANOPR | Early-stage; no NOPR issued | National framework under consideration; 20 MW definition |
Treat EL25-49-000 and EL26-70-000 as separate matters. The first is the PJM co-location proceeding opened in February 2025. The second is the MISO show-cause docket from June 2026. Filing strategy that conflates them will produce the wrong comment deadline and the wrong regional argument.
SPP's Tariff Filings: The First Enforceable Rules on the Ground#
SPP is the clearest prototype because its rules are accepted, specific, and already operating. FERC accepted the High Impact Large Load and HILL Generation Assessment revisions in ER26-247-000 effective January 15, 2026, subject to condition, then accepted Conditional High Impact Large Load Service on June 5, 2026.
90 days and $100,000 — SPP's HILL Delivery Point Study target duration and study deposit, with an additional $200,000 required if electromagnetic transient analysis is necessary.
SPP HILL Thresholds, Study Terms, and Operating Obligations#
| Parameter | SPP requirement |
|---|---|
| HILL threshold | Greater than 50 MW; also captures loads of at least 10 MW connecting at or below 69 kV |
| HILL Delivery Point Study | Designed for completion within 90 days |
| Study deposit | $100,000, plus $200,000 if EMT analysis is required |
| HILLGA System Impact Study | 90 calendar days from the review period |
| Paired generation cap | Amount needed to serve the HILL, or 125% to account for reserve margin |
| 765 kV proximity rule | HILLGA generator must be within one substation of the HILL |
| Ramp rate | No more than 20 MW per minute unless otherwise directed |
| Telemetry | Real-time telemetry required; separate telemetry and bill meter values for each conditional component |
| Disconnect | SPP must hold remote capability to disconnect the load from the transmission system |
Figures are drawn from SPP's HILL/HILLGA and Conditional HILL tariff record — the ER26-247-000 order, the Conditional HILL order, and their underlying filings. Confirm any single parameter against the operative tariff sheet before designing to it. Note the 20 MW-per-minute ramp limit specifically: it is an operating constraint on how fast a training cluster can come up, not a study assumption.
On timelines, the honest read is that the record does not support a clean comparison. Stage-by-stage duration tables for legacy versus new load interconnection are not published across regions. What is documented is SPP's 90-day study targets, MISO's 120-day approval goal, and MISO's statement that large-load projects now seek to connect in 18 to 36 months. Anyone quoting a tidy "legacy 18 months versus new 36 months" delta is extrapolating. Model schedule risk on the tail, not the mean.
NERC's Large Loads Action Plan: Guidance That Shapes Tariffs#
NERC published a Large Load Action Plan identifying data centers and other emerging large loads as presenting reliability risks that require new interconnection study methodologies, load-shedding protocols, and ride-through capability. Its accompanying white paper on the characteristics and risks of emerging large loads describes rapid ramp rates and high load-factor profiles that differ materially from the load assumptions embedded in existing interconnection tariff rules.
This is guidance, not a mandate. NERC's Large Loads Action Plan influences ISO tariff design; it is not a directly enforceable standard on a data center developer today. The mechanism by which it reaches you is a regional tariff that adopts its recommendations — which is exactly what SPP's telemetry and disconnect provisions represent.
The document to read for equipment scope is NERC's Reliability Guideline on Risk Mitigation for Emerging Large Loads, which specifies load shedding, ride-through, and operational flexibility recommendations that translate into on-site specifications. Its data recommendations are the leading indicator: peak net real power demand, a quarterly or yearly MW ramp-up energization schedule, load power factor, voltage and frequency disconnection thresholds, reconnection thresholds and ramp rates, and facility-level MW detail broken out by IT load, lighting, distribution, and cooling. If your region adopts that dataset as an application requirement, your electrical engineer produces it before the study opens, not during.
Co-Location, Behind-the-Meter Generation, and the FERC Dockets#
FERC ordered action on co-location issues related to data centers running AI workloads following its technical conference on large loads co-located at generating facilities, then found PJM's tariff unjust and unreasonable in December 2025 and directed transparent rules plus new transmission service options. FERC's June 2026 MISO order extended the same questions to that region.
The unresolved tension is visible in the Commission's own record. The Susquehanna co-location proposal in ER24-2172 drew a dissent from Chairman Phillips, who argued the Commission should have accepted the non-conforming agreement while gathering transparency filings over time. That disagreement — how permissive to be with behind-the-meter generation at co-located facilities before the rules are settled — is still live.
Co-location is not a bypass. It moves your project from one regulated pathway into another, with its own cost-allocation, metering separation, and transmission-service questions. Structure any co-location arrangement against the resulting PJM filings rather than pre-2025 practice.
Equipment Categories Triggered by the New Rules#
This is where tariff language becomes purchase orders. Three requirements in the accepted SPP orders and the PJM directive map directly onto hardware.
Regulatory Requirement to Equipment Scope#
| Regulatory requirement | Equipment category | Procurement implication |
|---|---|---|
| Real-time telemetry (SPP Conditional HILL) | RTUs, revenue and check metering, protective relaying, SCADA integration at the point of interconnection | Specify telemetry and protocol scope in the substation package before the study closes, not during commissioning |
| Remote disconnect capability (SPP Conditional HILL) | Medium-voltage switchgear with remote trip, motor-operated disconnects, transfer switches | Switchgear must be ordered to a spec supporting RTO-initiated disconnect and controlled reclose into your transfer scheme |
| Generation assessment (SPP HILLGA) | Behind-the-meter prime-power reciprocating engines and gas turbines | On a bring-your-own-generation request, generation scope becomes part of the interconnection record |
| Network upgrades assigned to the requesting load | Large power transformers, substation breakers, line terminal equipment | Upgrade scope can land after study completion — after financial close in many capital structures |
| Flexible or curtailable transmission service | UPS, station batteries, load-shed controllers, transfer switch logic | Curtailment obligations must be reconciled with tenant SLAs at the electrical design stage |
| Co-location cost allocation and metering separation | Revenue metering, protection separation, dedicated transformation | Metering architecture becomes a tariff compliance artifact, not a billing detail |
On the standards side, IEEE has an authorized active project, P4200, covering functional, performance, and interoperability requirements for data center interconnection with electric transmission and distribution systems — ride-through, post-fault active power recovery, protection coordination, ramp-rate management, and power quality. It builds on the interconnection methodologies of IEEE 1547, IEEE 2800, and IEC 62786, and was on IEEE's June 2026 standards board agenda. The project is in development, not published. Specify to it as design intent, not as a compliance obligation.
Because upgrade and generation scope can arrive after your study, the sourcing question shifts from "what do we buy" to "what can we get." The power system configurator and current generator inventory exist for that gap — sizing a compliant on-site package against real availability rather than a catalog lead time. Surplus and refurbished medium-voltage switchgear and large power transformers are the usual release valve when a tariff-driven upgrade lands post-close.
What to Do Before the Next Regulatory Deadline#
Tag every active and pipeline project by RTO and by interconnection request date. SPP's HILL rules took effect January 15, 2026. Requests straddling that date need a written determination on transition provisions, not an assumption — and FERC's grandfathering language for agreements already negotiated or nearing completion is the argument to make.
Read your region's show-cause docket. Every RTO filed a 30-day informational report in July 2026, and a show-cause response was due August 17 unless the region requested a stay to bring its own Section 205 reforms instead. Whichever path your region took, those filings are public and are the best available preview of the rules your next study will run under. In PJM specifically, watch the Price Adaptive Load Service model for flexible large loads, with a FERC filing targeted on or before November 16, 2026.
Scope the generation assessment and the telemetry and disconnect package before your study closes. After it closes, both become change orders. In SPP that scope is defined; elsewhere it is being defined right now.
Price a contingency for post-study upgrade assignment. Network upgrades allocated to the requesting load can arrive after financial close. The large load interconnection and data center power bottleneck briefings cover the sequencing math, and the substation transformer guide covers what a late-arriving upgrade costs in schedule.
If co-locating, track the dockets separately. PJM co-location is EL25-49; the MISO show-cause is EL26-70. Different matters, different deadlines. Where conditional service reshapes runtime and fuel sizing, the data center backup power analysis covers the design consequences.
FAQ: RM26-4, SPP HILL, and Data Center Interconnection#
What is FERC RM26-4 and does it apply to my data center project today?#
RM26-4-000 is an Advance Notice of Proposed Rulemaking on interconnecting large loads to the interstate transmission system — an early step where FERC gathers input before deciding whether to propose specific rules. It is not a final rule and not yet a formal proposal, so it does not bind any developer today. It defines large load as demand greater than 20 MW. The rules that actually govern your project right now are regional tariffs and FERC's region-specific orders.
How much longer does interconnection take under the new large-load study requirements?#
The record does not support a clean before-and-after number. What is published: SPP designs its HILL Delivery Point Study for completion within 90 days, MISO targets 120-day approval once studies are complete and agreements are signed, and MISO reports that large-load projects now seek to connect in 18 to 36 months. Stage-level durations for the new tracks are not published across regions, so treat any tidy delta you see quoted as an extrapolation.
What does Conditional High Impact Large Load Service mean for a data center operator?#
It is a service class SPP established under ER26-1323, accepted June 5, 2026, that lets a large load take service ahead of full network upgrades — in exchange for operating obligations. Those include real-time telemetry, separate telemetry and bill meter values for each conditional component, and remote capability for SPP to disconnect the load from the transmission system. Operationally that changes transfer switch logic, load-shed philosophy, and what you can commit to a tenant in an SLA.
Is co-location at a power plant a way to bypass new interconnection rules?#
No. FERC found PJM's tariff unjust and unreasonable in December 2025 specifically for failing to provide clear and consistent treatment of co-located load, and directed PJM to create transparent rules and new transmission service options. Co-location moves a project into a different regulated pathway with its own cost-allocation, metering separation, and transmission-service obligations. The Susquehanna proceeding shows the Commission is still divided on how permissive to be, which is itself a reason to structure conservatively.
Which specific pieces of equipment do I need to procure differently because of these rule changes?#
Three categories change first. Telemetry and metering scope expands at the point of interconnection — RTUs, protective relaying, and SCADA integration specified during the study rather than at commissioning. Medium-voltage switchgear must support RTO-initiated remote disconnect and controlled reclose. And on a bring-your-own-generation request, the on-site generation package becomes part of the interconnection record rather than a parallel procurement. Network upgrade equipment is the wildcard, because that scope can be assigned after the study closes.
What to Do This Quarter#
Pull your active projects, tag each by RTO and request date, and get a written determination on transition provisions for anything filed before January 15, 2026 in SPP or before PJM's post-December 2025 filings. Then read your region's August 17 show-cause response and scope the generation assessment and telemetry package against what it proposes — because once your study closes, both become change orders. Compare your compliant on-site generation and switchgear options against real availability using the power system configurator before the next study cycle locks your assumptions in.