37 Installation, repair, maintenance, overhaul, upgrading, modification, refurbishment, restoration, conversion and preservation services, all for vehicles, excavators, power operated machines, construction machines, machines for processing waste, machines for sorting rubble, silt, sand, gravel, rock, stone or organic material, machines for grading rubble, silt, sand, gravel, rock, stone or organic material, trommels and lifting apparatus; installation, repair, maintenance, overhaul, upgrading, modification, refurbishment, restoration, conversion and preservation services, all for electrical equipment and apparatus and instruments for conducting, switching, transforming, accumulating, regulating or controlling electricity; installation, repair, maintenance, overhaul, upgrading, modification, refurbishment, restoration, conversion and preservation services, all for effluent treatment installations to separate water from contaminants, devices for the separation of oil from water, effluent treatment machines to separate water from contaminants, water treatment units, water treatment apparatus, installations for the treatment of water and waste water treatment apparatus; installation, repair, maintenance, overhaul, upgrading, modification, refurbishment, restoration, conversion and preservation services, all for apparatus for the removal of suspended solids from a liquid, devices for the separation of impurities from water and installations for the separation of liquids; erection of steel structures, hoppers and conveyors; electric appliance installation, maintenance and repair; installation, maintenance and repair of electrical wiring; installation, maintenance and repair of machine tools; installation, maintenance and repair of storage systems; leasing, rental and hiring of excavators, lifting apparatus, power operated machines and construction machines