The FL-I device is a single-pole voltage detector. This device is designed to detect operating voltages clearly indicating either the “voltage present“ or “voltage not present“ state. This device does not have a built-in power source (battery) and thus no self-test function. For transportation purposes, the insulating element can be removed from the display unit with the contact electrode. According to the German accident prevention standard DGUV Regulation 3 (Table 1c), the device is subject to maintenance tests with minimum intervals of at least 6 years.