Western had instructed a group of 15 employees to replace overhead power lines with insulated cables, Truro Crown Court was told.
On the evening of 16 January 2013, linesman Ryan Thomas was working up an electricity pole. One of his colleagues cut a connecting wire and this caused Thomas's pole to fall to the ground while the 28-year-old was still attached. He sustained internal injuries and was pronounced dead at the scene.
The Health and Safety Executive (HSE) investigated and found that the work had not been properly planned. It said the workers had not received a detailed procedure for replacing the cables and the risk assessment failed to consider that the job was being carried out at night.
The communication of work methods and on-site coordination were also inadequate.
Western Power Distribution, which covers the south west, the Midlands and South Wales regions, pleaded guilty to breaching s 2(1) of the Health and Safety at Work Act. It was handed an £800,000 financial penalty plus costs of £113,115 on 29 June.