The new peak at 28,351.7 megawatts was recorded at 2.17pm, when the temperature was 36.6 degrees Celcius amid high humidity.
Power demand from the industrial, service and household sectors increased.
It is the second power peak recorded this year. This year's first peak at 27,639.3MW was registered on April 6.
Egat also noted that power usage in the South hit a new peak yesterday at 2,630MW, an increase of 5 per cent or 125MW from last year, as the number of air-conditioners increased.