Tina Brown watched in horror as her 11-year-old cob Merlin writhed in agony for two hours after collapsing on a grass verge next to Station Lane, East Ardsley, near Leeds, at 4.20pm on Wednesday.
Ms Brown and others tried to move Merlin but were beaten back by electric shocks.
A vet finally managed to sedate the horse but an electric current continued to surge through the horse's body before he finally died, according to Ms Brown.
It was only at 10pm that Ms Brown, who runs the Foxholes Animal Hotel in nearby Moor Knoll Lane, received a phone call from a police officer telling her the site was safe and the carcass had been removed by truck.
The body was cremated the next day.
Police
Ms Brown, 54, told the YEP that police officers arrived at the scene not long after her horse was struck down.
She said: "Why did it take so long for someone to come from the electricity board when the police rang them straight after they arrived? I heard them making the call.
"When someone did arrive two hours later they couldn't do anything.
"What I also can't understand is why Merlin was still getting shocks through his body hours after he fell.
"He bolted when it first happened and we were at least a hundred yards down the road from where he got the shock."
An investigation has been launched by the Health & Safety Executive.
Police have also removed a length of cable from the scene where contractors CR Reynolds Construction Ltd were installing kerbs for Leeds City Council.
A West Yorkshire Police spokesman confirmed it received its first call at 4.38pm and that its officers at the scene contacted the council at 4.52pm
The YEP understands that an YEDL engineer received a call at 5.25pm.
He was on site by 6.15pm and repairs were completed by 10pm, although it is not clear when the current was switched off.
CE Electric owns Yorkshire Electricity Distribution Limited, which is responsible for the distribution of electricity across the region.
A CE Electric spokesman said: "We cannot comment on this matter until the result of the HSE inquiry is complete.
"We offer our sympathies to the horse's owner and we will co-operate fully with the HSE throughout its investigation."
A Leeds City Council spokeswoman said: "We are helping the Health and Safety Executive with their investigation as well as carrying out one of our own. "It would be unwise to draw any conclusions until we have the results of these investigations."