WASHINGTON, Oct. 16 -- For two afternoons this week, the grid operator for 13 states and the District of Columbia paid customers to use less electricity, while keeping in reserve a federal order that would let it push data centers onto their own generators.

PJM Interconnection says it did not need that power. It called demand response, the programs that pay homes and factories in advance to cut their use, on Tuesday and again on Wednesday, but said its alerts required no action from customers. It is the same grid that hit a power grid emergency on July 4.

What made this week unusual is that the weather was warm, not extreme. Autumn is when generator and transmission owners take equipment offline for repairs and construction, and the war...