Answer: Ratchet gets tangled in power lines and falls to the ground.
Ratchet doesn't see the power lines and runs into them, knocking himself down, which causes the house and ground to shake. His response is, "Wow! That was tingly! You've got to try that!" Ironhide, who is watching Ratchet trying to stand back up, sarcastically says, "Yeah, that looks fun." Later in the same scene you see similar sparks through the window of the house and the ground shakes again. Sam's dad shouts, "Aftershock!", and jumps in the bathtub. One can assume that Ratchet probably hit more wires.