Here is an odd comment I found on NYC blackout from 1977.

At 9:24, the ConEdison operator tried and failed to manually shed load by dropping customers. Five minutes later, at 9:29 p.m. EDT, the Goethals-Linden 230 kV interconnection with New Jersey tripped, and the Con Edison system automatically began to isolate itself from the outside world through the action of protective devices that remove overloaded lines, transformers, and cables from service.

https://en.m.wikipedia.org/wiki/New_York_City_blackout_of_1977