HOUSTON -

If rolling blackouts are ordered to help deal with excessive power usage to combat the heat, areas on the northwest side of Houston have the highest chance of being turned off first.

On Wednesday, the Electric Reliability Council of Texas said Texas was under an emergency alert level 1. At level 3, the state requires rolling blackouts. The difference between the levels depends on the amount of electricity being used and how much is being generated, which changes daily.

CenterPoint has a list of the areas that will be affected by rolling blackouts when they are ordered.

Residents along Highway 6 in northwest Harris County are more likely to get their power pulled, officials said. Power was cut off to the area during the last round of rolling outages, which occurred in February during a severe cold snap.

"It was not done by ZIP code. It was done by major lines," said Floyd LeBlanc with CenterPoint Energy.

He said the entire Houston area is divided into three groups. A map shows the areas that will be included in rolling blackouts. The highest concentration was on the northwest side -- north of Interstate 10 and south of Highway 6.

But CenterPoint said which homes and businesses selected to go dark first is top secret.

"Homeland Security regulations don't allow us to show what is on which line, so we're not going to talk about who's on which line. That's against he law in these post-9/11 days," LeBlanc said.

State officials said they have only required rolling outages three times since 1989.