Every summer, four fifteen-minute windows quietly set a large share of what many commercial customers will pay for transmission the following year. Most businesses never find out which four intervals counted, or what their meter was doing at the time.
What 4CP is
4CP stands for four coincident peaks. ERCOT identifies the single fifteen-minute interval with the highest systemwide demand in each of June, July, August, and September. That gives four intervals per year.
For customers on interval data meters above a certain size, the utility looks at how much power that facility was drawing during those same four intervals. The average becomes the basis for transmission charges for the following calendar year.
Why it matters more than it sounds
Four intervals out of roughly 35,000 in a year can drive twelve months of charges. A facility that happened to run hard on a hot weekday afternoon in July carries that number into every bill the next year, even if the rest of its summer was ordinary.
It also means two businesses with the same total usage can pay very different transmission costs. The difference is timing, not volume.
Why a fixed contract doesn’t cover it
Transmission is a regulated delivery charge. It passes through from the utility regardless of which supplier you use or what rate you locked. A fixed-price supply contract protects the commodity component, not this line. That is why it is worth knowing where your 4CP number came from.
When the peaks tend to land
No one knows the exact intervals in advance. ERCOT confirms them after the season ends. In practice, summer peaks usually fall on the hottest weekday afternoons and early evenings, when air conditioning load across the state is at its highest. Growth in solar and batteries has started to shift when the grid feels tightest, which makes the pattern worth watching rather than assuming.
What to check now
Once the season closes, line up your interval data against the four confirmed peak intervals. Then check three things: whether the demand billed matches your meter, whether the facility is in the right tariff class, and whether any of those peaks came from load that could have moved. Some operations can reduce exposure next summer by shifting flexible load away from likely peak hours.
Sector 7 reviews commercial bills at no cost, including how transmission charges were set →