PJM Interconnection, the regional grid operator covering thirteen states from Illinois to North Carolina, must file its revised co-located load tariff with FERC (Federal Energy Regulatory Commission) on Monday 18 May. The filing follows FERC's 16 April order, which accepted PJM's reformed interconnection pathway but rejected the operator's redefinition of co-located load and its attempt to alter behind-the-meter rules 1. The deadline is the immediate regulatory step before RM26-4-000, the main rulemaking on loads above 20 MW that FERC pledged to act on by end-June .
The specific question PJM must answer is technical but consequential: when a generator (typically a gas turbine or a battery system) sits on the same campus as the data-centre load it serves, how is that arrangement classified for tariff purposes? PJM's preferred definition would have allowed a wider category of behind-the-meter configurations; FERC ruled the definition would let load avoid contributing to grid costs in ways the commission was not prepared to accept. The new filing has to thread between the FERC objection and the operating reality of the Loudoun cluster, where co-located generation is already being designed into 2027-2028 builds.
The stakes sit directly on the Loudoun, Fairfax and Prince William corridor that PJM serves. Operators designing campuses there now face a planning environment where rezoning has narrowed (the Digital Gateway abandonment closes one path, Fairfax's new rules write a tighter one) at the same time as the federal tariff language defining their preferred behind-the-meter configurations is being rewritten. The 18 May filing is the document the colocation engineers in that corridor will read on Tuesday morning to find out which configurations remain viable. RM26-4-000 then becomes the federal template against which ERCOT, CAISO and MISO will be benchmarked over the second half of the year.
