Firefighters from the San Bernardino City Fire Department were called to the residence Friday morning, and told by a 17-year-old girl that her family was injured and collapsed in the yard.
But it was deemed unsafe to rescue them.
Once one person was getting shocked, we think that the wife was trying to assist and the son was trying to assist and unfortunately they all succumbed to their injuries, said Jason Serrano, fire department spokesman.
"It was a very unfortunate accident," Serrano said.
Investigators believe the father went outside to check out the loud popping noises, and in the dark failed to see the downed live wire.
The deceased are identified as a 43-year-old man, 42-year-old woman and a 21-year-old man.
The utility company was called to cut the power to the arcing 12,000-volt electrical line.
High winds of up to 95 km/h caused the line to fall, Serrano said.
A 17-year-old girl and 10-year-old, home at the time, were uninjured and are staying with family members.
San Bernardino is 88 kilometres east of Los Angeles.