Sam Cunningham's friends called emergency services, who alerted the rail network to stop trains on the main line between Manchester and Wigan.
The 16-year-old is now being treated for severe burns in hospital, where experts say he is "lucky to be alive".
Sam was retrieving a rugby ball on the bridge near his home in Wigan on Thursday evening when a charge leapt from overhead powerlines into the steel toecaps of his boots.
He was knocked unconscious by the fall and all his clothes were burned off.
After paramedics arrived Sam regained consciousness and managed to phone his mother Ann.
Miss Cunningham, 40, a health care assistant, said: "I got there within a couple of minutes and all his clothes had been burned off, he was shaking from head to toe.
"All his hair had been singed and smoke was coming from the bandages paramedics had put on his legs. I can't believe that he is still alive - I don't think anybody can."
She said her son could not remember what happened except 'seeing a flash and then feeling himself spinning around'.
The teenager is being treated in the specialist burns unit at Whiston Hospital, Merseyside. He will need skin grafts but is expected to make a full recovery.
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Mum Ann saw smoke coming off Sam's bandages
Sam's clothes were burnt off by the electric shock
Experts said last night that Sam, a labourer, was lucky to be alive. Phil Mawby, a professor of engineering at Warwick University, said: "The current going through an overhead railway cable would easily be strong enough to kill somebody.
"It would burn its way through the skin and in some cases stop a person's heart."
He said that Sam must have been within a foot of the power cable for the charge to jump through the air into his body.
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He went to fetch a ball when the volts were attracted by the metal toe caps in his boots
A spokesman for Network Rail said: "It is incredibly rare for anybody to be struck by an overhead power cable.
"If someone is electrocuted, it is normally because of stepping on the live cable running alongside the tracks."
A British Transport Police spokesman said: "We would like to reinforce that the railway environment is a highly dangerous place and advise that no person should go on or near the railway lines in any circumstances."
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