Chris Halton, 56, said the late woman, killed on an undisclosed date, spoke to him two months after she was killed to say she was “very grateful” of his attempt at saving her.
Mr Halton, an ex field intelligence officer for Essex Police, said he was driving on a country road in the county when he heard a voice in his head “screaming” as he approached the apex of a bend.
He said: “I braked hard and a car came around my side, which narrowly avoided colliding, and it drove off at high speed, it was really weird.”
The policeman said he then got wind of a traffic accident in the area, on the border with Suffolk.
He added: “I drove up there and discovered a Dutch-registered Volvo that had hit a power pole and brought the cable down.
“There was a 100,000 volts cable hanging across the road. A lady in a house nearby came out with a cup of tea for another policeman to drink, but the cable went round her neck.”
He said: “When I got there she was laying on the ground, but I did not see the cable.
“He (other policeman) said ‘don’t f***ing move, you could hear the energy from it.”
However, he told the Paraforce UK paranormal conference in Witham, Essex, that he was able to get to her, and he “spent 20 minutes trying to revive her with mouth to mouth resuscitation.”
Despite this there was nothing he could do, and she had no pulse.
Mr Halton said the whole incident was extremely upsetting for everyone involved and left him in tears.
He said: “Two months later a friend who is a medium said to me ‘I have got this lady here who wants to say something’. It really triggered me.
“‘She said she saw you tried to save her life, she saw you crying, she is very grateful you tried to save her life and has come back to say thank you.
“It was life changing in my work.”
The medium also told him that his late grandmother ‘is always with you and there to guide you.’
She added: “If she could show her place in anything, she said she will.”
Mr Halton said that two weeks later he received another shock, seeing the ghost of his grandmother.
He said: “I came home in my police uniform and sat in the corner in her chair was my nan.
“She was browny green, glowing and completely stationary.
“She never moved and never responded, my girlfriend could not see her, but two cats walked in and saw her and stared at her.
“I’ve felt here presence around me when things go bad since this.”
He described another bizarre on the job experience, saying that when he was interviewing a man, a voice told him he was “innocent.”
Mr Halton added: “And I proved he was innocent.”
He said his paranormal experiences began as a child when he had the “ability to see things no one else could”, but he was pressurised by those close to him not to believe.
He said: “I would see people dressed in strange clothes who were not there.”
After retiring from the force, Mr Halton now runs the paranormal YouTube channel Haunted Earth TV, and films himself in historical locations looking at their history and any paranormal events.
He is known as the Man in the Hat due to his trademark accessory he wears.