Congestion in the California ISO market shows up as a shadow price on a specific piece of equipment — a transmission line, a transformer, or an operating nomogram. This page ranks those constraints two ways: how often each one binds, and how hard it hits when it does. The two lists are not the same, and the difference is usually the interesting part.
Frequency and severity measure different risks. A constraint that binds in most hours at a few dollars per megawatt-hour is a chronic, predictable feature of the network — it shapes where power is worth producing, but rarely surprises anyone. A constraint that binds twice a month at $4017 per megawatt-hour is the opposite: mostly invisible, then briefly dominant. Traders, schedulers, and planners tend to care about different ends of that spectrum.
Voltage is a useful second signal. Lower-voltage elements — 60, 69, 70, and 115 kV lines — appear frequently in the severity ranking because they serve local load pockets with limited alternative paths, so a single outage or a hot afternoon can push them to their limit. Higher-voltage 230 kV and 500 kV constraints bind less often but move much more power when they do.
Rankings are built from CAISO OASIS market results (PRC_NOMOGRAM for internal constraints, PRC_CNSTR for interties), collected automatically and refreshed on this page weekly. They reflect what has been observed since tracking began — a 47-day window, not CAISO's full history, so a constraint that was severe last winter will not appear until it binds again. Internal and intertie counts come from feeds with different retention windows and should be compared within a section, not across them. Constraint names are parsed from CAISO's identifiers, so substation abbreviations follow CAISO's conventions. This page is informational only and is not trading, financial, or operational advice.