Electric installation design is the most important part in a multi-storey building functioned as a layout for tools that used electric as its operational, by calculating resistance, current, and power, so the use of electrical power can work well and appropriate. In the Ar+otel Hotel, Yogyakarta, the designer designed 9 floors of the installation not including the rooftop and basement, the design covered some tools such as lighting, outlet, VAC electrical power supply (arrangement of air and mechanical ventilation); electric charge (MATV, CCTV, lift, telephone, fire alarm, and sound system); electrical device supplies (clean water pump, hydrant pump, fire pump, hot water pump, Pressurized fan, summit pump, deep weel); low voltage installation, and generator set installation or transformer. After did the calculation of the Ar+otel Hotel electric installation, it produced the installed entire charge of 405.213 KW and the reactive power amounted to 506.516 kVA with 0.8 of the cosphi (as stated in MEP). Based on the power that had been produced, the transformer and generator capacity used to 630 kVA. By the 20 kV of middling voltage in installed PLN supply, 555 kVA power capacity, 3 phases, 50 Hz. The used transformer and generator was 630 kVA. In order to repair the power factor became 0.9 with the charge of 450.326 kVA, it was done by installing the bank capacitor of 100 kVAr with the combination of 10 step x 10 kVAr.