Anthony Andre, 42 of Fulham Road, went onto the railway line at around 6.30pm on September 10.
Power was switched off to the electric rail, which powers trains through the Clapham area.
Andre was quickly removed from the tracks and arrested but his actions resulted in 38 trains being partially or fully cancelled and caused a total of 3,427 minutes worth of delays to passengers during the evening rush hour.
Clapham Junction is the busiest UK station for interchanges between services, though London Liverpool Street handles the most passengers.
He was remanded in custody and appeared at Wimbledon Magistrates Court on September 12, where he pleaded guilty to trespass and obstruction, and sentenced to eight weeks in prison.
Speaking on behalf of Network Rail, Southern Railway and South Western Railway, Paul Langley, Head of Security, Crime and Resilience, said: “Trespassing on the railway is incredibly dangerous.
“Trains in the south east are powered by the electric rail, which carries 750 volts and easily enough to kill or cause devastating life-changing injuries.
“We hope this sentence sends a message that trespassing on the railway will not be tolerated.
“Anthony Andre is lucky to be walking away with a prison sentence, as it could have ended in tragedy.
“His actions not only put his own life at risk, but caused huge disruption for thousands of passengers trying to get home, or to see friends and family.
“We work hard every day to keep people safe and trains running.
“Incidents like this are a stark reminder of how quickly things can go wrong, and why we always take trespass so seriously.”
Investigating officer PC Darren Ryan said: “Not only is trespassing exceedingly dangerous, potentially resulting in life-changing injuries or even death, but it’s also illegal and we will take firm action against those that break the law.
“Andre chose to trespass during a week of strikes, causing even further disruption and chaos for the network, so I’m pleased with the result in this case.
“I would urge members of the public who witness incidents of trespass to contact us by texting 61016 or call us on 0800 40 50 40 so that we can help prevent any tragic accidents from taking place on the railway lines.”
