Data quality and corrections
We publish corrections to our data, including what changed and how many records it touched. Corrections made before a customer saw the data are listed too.
How we classify capacity
- Load-serving headroom: substation headroom calculated from transformer ratings minus observed peaks, or estimated by summing feeder headroom.
- EV hosting capacity: capacity the utility publishes for EV charging use, estimating remaining circuit load capacity to guide charging developers.
- Electrification headroom: how National Grid’s figures are labeled in our data. The National Grid portal guide describes electrification estimates for transport and heating.
Corrections
Entries for September were added to this record on September 27, 2026; later entries carry their own dates.
Con Edison, winter feeder values (September 2026)
What happened: Winter feeder values were not being read from the source field designated for winter capacity.
What changed: We corrected them using the designated field.
Records affected: 857 winter feeder values.
Central Hudson, substation values (September 14, 2026)
What changed: We corrected substation capacity values after removing duplicate feeder records and applying source values in their reported units.
Records affected: 54 substations (108 seasonal values).
Central Hudson, coverage (September 14, 2026)
What happened: Ten substations were no longer present in the source data.
What changed: We retired them. Their historical snapshots remain available.
Records affected: 10 substations.
Orange & Rockland, substation methodology (September 14, 2026)
What changed: We updated substation values to the published normal transformer rating minus observed seasonal peak load. These values suit rapid feasibility screening but do not account for Orange & Rockland's likely N-1 contingency margin. Final interconnection feasibility requires Orange & Rockland confirmation.
Records affected: 555 stored snapshot records are now classified as load-serving headroom. 97 earlier annual rows were replaced by seasonal rows.
United Illuminating, substation values (October 2, 2026)
What happened: Feeder-derived substation values were overstated because historical snapshots from renamed feeders were included.
What changed: Seven values were corrected downward by a combined 79.8799 MW.
Records affected: 7 substation values. Made before customer onboarding.
United Illuminating, coverage (October 2, 2026)
What happened: Stale circuits remained current after source naming changes.
What changed: We retired 31 feeder circuits and 4 substation circuits. Historical snapshots remain available.
Records affected: 35 circuits. Made before customer onboarding.
Known limits
- National Grid values are labeled electrification headroom, not load-serving headroom.
- A snapshot date is when we stored a reading. The source date is the date the utility gives for it; some sources give none.
- Rhode Island Energy values are in MVA, even where a field name says MW.
- Substation values for Central Hudson, PG&E, CMP, Rhode Island Energy, United Illuminating and SDG&E are sums of feeder values, not native transformer headroom. Central Hudson sums one value per unique feeder, and transformer ratings may impose a tighter limit. Recorded minimum and maximum values are individual feeder bounds.
- Orange & Rockland's calculation does not include the N-1 margin. Verify planning methodology before finalizing feasibility.
- Con Edison: Manhattan below 96th Street is not in the source layer. Con Edison and United Illuminating are EV hosting capacity, not load-serving headroom.
- CMP source values are in kW and converted to MW.