The sub-contractor admitted a catalogue of failures which led to the accident which left Gregor Steele, 20, needing surgery to have his leg amputated above the knee.
Gallagher Groundworks Ltd was fined at Perth Sheriff Court after it admitted being responsible for the "life-changing" injuries to Mr Steele at the Griffin Wind Farm in Aberfeldy, Perthshire.
The Crieff-based company - which has around 14 employees and a £1.4 million turnover - was told by a sheriff it had committed a serious breach of health and safety rules.
Mr Steele was trying to pour water from a bowser on to an overheating rock-crusher when he was crushed between two heavy items of plant in September 2010.
The court was told that the tractor he was driving was only capable of pulling three tonnes safely and the water bowser, when full, weighed up to 12 tonnes.
Fiscal depute Gavin Callaghan said that even if the bowser was empty it was still too heavy for the tractor to tow safely. It was the weight which dragged the tractor when it was parked and left Mr Steele trapped.
Mr Callaghan said the tractor had two braking systems, but only one of them worked properly, while the other had a note taped over it to tell the driver it could not be operated. He said the company had been using it in that condition for five months.
He said: "The Health and Safety Executive revealed significant deficiencies in relation to the braking of the tractor. This was at the construction site for the Griffin Wind Farm.
"Even when it was empty the bowser exceeded the weight the tractor was capable of towing. Various witnesses saw it roll backwards."
He told the court that Mr Steele was dragged free of the machinery and airlifted to hospital. The decision was taken to amputate his left leg a few days later.
The court was told that he was unable to work for two years but had since returned to work for Gallagher Groundworks and was able to drive automatic tractors.
Solicitor Gordon Keyden, defending, said: "This was an unfortunate and very serious accident. The weight of the bowser is the nub of the issue. That's what caused the tractor to be dragged backwards. The accused accepts responsibility for the failure to identify the fact this bowser was too heavy for this tractor. That was the true cause of the accident."
The company admitted failing to ensure the safety of its employees at the wind farm between August 13 and September 3, 2010, which led to their employee being injured.
The company admitted that Mr Steele was left "severely injured, permanently disfigured and permanently impaired" as a result of crushing injuries on September 3, 2010.
Sheriff Fiona Tait said: "The court must take the view this is a serious breach. I must have regard to the injuries sustained by Mr Steele, which are properly described as life changing."