High-voltage Apparatus Repair and Testing HART High-voltage provides total substation maintenance services, including testing, maintenance, repair, start-up/commissioning, upgrades and retrofits. We deliver fast emergency service, accurate and affordable testing and preventive maintenance to keep your plant running. HART offers the "next generation of service", with highly skilled and experienced field engineers, state-of-the-art testing equipment and a proven track record. From high-voltage substations to 480V switchgear, we have the personnel, equipment and expertise to provide top-notch workmanship and safety. Call us for a quote, job walk, site assessment or emergency service: California: 530-755-3126 Nevada: 775-358-0773