UNINTERRUPTIBLE POWER EQUIPMENT

PURPOSE:To prevent the damage of load due to erroneous connection by providing a determination means detecting the correct connection of the grounding phase of a constant voltage constant-frequency power unit (CVCF), to which an AC power is input, from the voltage to the ground of the grounding phase. CONSTITUTION:When the grounding phase of an uninterruptible power equipment 10 is connected erroneously to the non-grounding phase of a power unit, output voltage from a ground voltage detector 6 is generated largely, and a decision circuit 7 decides the connection to be erroneous connection and interlocks e CVCF control circuit 8, and outputs a signal operating an alarm circuit 9. Accordingly, erroneous connection is determined at a glance while a CVCF. 3 is not operated by interlock, thus preventing the situation causing the damage of an overvoltage inhibitor 5 on the load side.