Why does thunder take about a second to hear when lightning strikes 20 meters away? Light travels much faster than sound. This explains why, for example, when you see lightning strike a kilometer away the sound takes about three seconds to be heard.
However a very close strike was perceived with the eye - and the power of the house tripped at the same time as the lightning strike was seen (exactly 20m). However the "crack" sound of the initial thunder (not the echo) was delayed - it took exactly 1.5 seconds from the visual bolt.
Why is the sound of thunder delayed when lightning strikes very near by?
Update:
The more pertinent question may be - What is the source of the sound of the lightning? What is the distance of that sound to the point of contact on earth?
 A: It doesn't - assuming you mean that there was no loud immediate sound at all, not that you heard one or more sharp cracks and then, later, a more traditional thunder sound. A lightning strike is (among other things) an explosion.
The idea that the lightning was 20m away is not an observation, it is a conclusion, and an incorrect one.
Your actual observation (guessing based off of your post) is that you saw a bright flash and at approximately the same time you saw the lights go out in a house approximately 20m away. Then approximately 1.5 seconds later, you heard a boom. (Not exactly! Fake precision can only increase the likelihood of misinterpreting observations!)
These observations are consistent with a lightning strike about 300-700m away.
A lightning bolt is a consequence of and contributor to a large, complex, rapidly changing electric field. The range of these changes is small in air (the magnitude of the induced voltage varies roughly as the inverse square of the distance to the lightning bolt, although the ground is a weak conductor that adds some complexity to that approximation). However, conductors (like a power grid) can transmit these changes over long distances at close to the speed of light - meaning that if something doesn't stop them on the way, they'll show up at your house's electrical system at about the same time that you see the flash.
Power grids are designed with this fact in mind and are hardened against surges caused by both direct lightning strikes on power lines or power poles and surges caused by nearby lightning strikes that cause a lightning-induced voltage on the lines. However, these protections are not absolute, especially over short distances.
I suspect that somewhere in that 300-700m donut, there are above-ground power lines; that the lightning struck somewhere along or near to them; and that this induced a high voltage, which tripped your main breaker.
