Ashley Coe, an agency worker, working on site for Pascon Limited was part of a group of workers laying cables in a trench when the incident happened on the 13 March 2013.
An excavator being used for the task tracked underneath a 33kV overhead power line and struck the power line.
Coe was helping to control a cable drum suspended from the arm of the excavator when the incident occurred.
Exeter Crown Court heard that work was taking place by British Solar Renewables Limited (BSR) to install a solar farm on site at Knockworthy Farm, Great Torrington, Devon.
Despite the high risk work being undertaken, BSR failed to install goal posts and signage to warn of the presence of overhead power lines in the area.
Subcontractor Pascon Limited who were installing the cables in the trench had failed to assess the risks of working under the overhead power lines, and subsequently had not appropriately planned, managed and monitored the work in order that it could be carried out safely.
As such they were using an unsafe method of installing the cables in the trench which ran underneath the overhead power lines.
As a result of the 33kV electric shock Coe suffered a life changing brain injury and had to be resuscitated by attending paramedics.
The court heard he has been affected in many different ways.
As a result of his injuries he suffers with short term memory loss, has some mobility issues and now no longer feels pain.
His speech has been affected and he has lost much of his independence. He is unlikely to ever work again. Two other workers received shocks but escaped serious injury.
Principal Contractor British Solar Renewables Limited of Glastonbury, Somerset, was charged with breaching CDM Regulations and received a £250,000 fine and was ordered to pay full costs of £72,466.
Subcontractor Pascon Limited, of Walsall, West Midlands was fined £35,000 plus £25,000 contribution to costs after admitting a CDM breach.
Speaking after the hearing HSE Inspector James Lucas said: “This incident was entirely preventable and arose from clear failures to plan, manage and monitor the work and to ensure that the construction site was set up with appropriate measures to control the risks of working under overhead power lines.
“Luckily Mr Coe was resuscitated, but he now suffers from life changing complications due the electric shock he received. He was extremely close to losing his life and this is down to the failure of both construction companies involved in the work.”