Control relay for monitoring of 3-phase networks with neutral (H3USN) and without neutral (H3US). Adjustable switch at the front for adjustment of correct voltage in 3-phase networks. The switch's position is not registered until the operating voltage is switched on. If the switch position is changed during operation, all LEDs (LED indications) begin to flash but the unit will continue to function normally with the voltage that was set at the most recent power connection. Monitors under-voltage between the phases that can be set between -2 % and -20 % of Un (measurement voltage) and over-voltage that can be set between 2 % and 20 % of Un. Each limit (over-/under-voltage) has its own relay output (R1 Over and R2 Under) and there is an adjustable time delay for each relay output (Tt1 and Tt2), adjustable between 0.3-30 s. H3USN also checks for neutral interruption. Green LED (Un) indicates supply voltage OK. Yellow LED (R) indicates active relay output.