Line crews with the Los Angeles Department of Water and Power, seen here atop a pole replacing a transformer on Sunday, July 8, 2018, work to restore power to thousands during the weekend's heat wave in the region. (Photo courtesy LADWP via Twitter)

Been sweating bullets? More than 90,000 people lost power in greater Los Angeles during this weekend's heat wave. And as of Tuesday morning, the LAWDP said about 700 still didn't have it back. Wondering what happened? Here you go:

How, exactly, does heat cause a power outage?

First, demand for power rises during a heat wave, as more people switch on their air conditioners. And when it's hotter, your fridge, freezer and AC have to work extra hard to cool the air, which requires even more power.

Sometimes there's not enough electricity being generated to meet all the extra demand. In other words, it's a problem with supply.

Power demand on July 9, 2018, when temperatures reached 95 degrees in downtown Los Angeles on the third consecutive day of a heatwave in Southern California, is shown in orange. Demand far outstripped power usage from July 1, 2018, shown in blue, when temperatures maxed out at just 78 degrees in downtown Los Angeles. (Courtesy: CALISO)

Ok, I get it. Not enough power to go round, right?

Yes. Except that's not what happened this weekend.

There was plenty of power available, said Steven Greenlee with the California Independent System Operator or CALISO, which manages how much power is coming onto the California grid.

"At least this time we squeaked through," he said.

That's because grid operators like CALISO have to build enough transmission so that a supply-related blackout won't occur more often than once every 10 years, according to Lori Aniti, an energy economist at the US Energy Information Administration.

So what did happen, then?

The problem was the electricity distribution system: the local network of poles, wires and transformers that are operated by utilities like LADWP or SoCal Edison.

Typically, power demand surges in the afternoon and evenings when people come home from work and turn on their air conditioners. It usually begins to die down around 9:00 p.m. as temperatures drop.

But during heat waves, it's hot at night. So people keep running their ACs while they sleep, and fridges and freezers keep working hard after dark. That means transformers don't get a chance to catch a break, or to cool down.

And that can cause transformers to break, according to SoCal Edison spokesman Robert Villegas.

"No piece of equipment is designed to run at 100 percent capacity of the time, forever," he said. "A piece of equipment can fail due to the continual strain."

When an outage happens, utilities send a "troubleman," an old-fashioned word for a very experienced electrician, out to assess the damage and figure out what needs to be replaced or repaired. The troubleman then calls in a crew to make the fix.

Both SoCal Edison and LADWP say they are working around the clock to restore power. LADWP brought in contractors and employees from other parts of the state to get the grid back online.

Good to know. But still frustrating for those who lost power.

Yep. Like Brian Fritch, who lost power for more than 60 hours in El Sereno this weekend. He'd like to see the utilities get ahead of the problem.

"Why wait until the transformer goes out? It's old," he said. "I don't know how much preventative maintenance they do but it seems like they're reactive more than proactive."

This story is part of Elemental: Covering Sustainability, a multimedia collaboration between Cronkite News, Arizona PBS, KJZZ, KPCC, Rocky Mountain PBS and PBS SoCal.

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