This voltage & frequency protector is recommended for use in AC parts of photovoltaic systems or other types of AC electrical installations. After connecting the PZH HUF to the monitored system and after the initialization of its internal electronics, the in-built switching contact for external contactor control closes. Subsequently, there is a continuous monitoring of two basic variables connected to the AC power supply system (specifically, voltage and frequency) and in case of deviation from the preset values, this contact opens and consequently the external contactor is dropped. In this way, it is possible to immediately disconnect all protected devices from the monitored AC network. PZH HUF 003 is suitable for use in three-phase or in one-phase applications since reconfiguration of measuring mode is made automatically by in-built microprocessor. The basic working limits of overvoltage / undervoltage / frequency and basic response time are set by producer. Alternative changes to these limits at the customer may only be performed by an authorized person (service technician) after connecting to the PC.