Abstract: An alternating voltage detector having a sensor for the detection of an electric alternating field, an electrical signal transducer connected to the sensor for signaling an electrical alternating field detected by the sensor, and an indicator unit connected to the electrical signal transducer for the indication of the signaled electrical alternating field, has an interference pulse filter arranged between the sensor and the electrical signal transducer which filters out electrical pulses or pulse packets detected by the sensor which have an average pulse duration or average pulse packet duration less than a predetermined time.

Abstract: The invention relates to a method for determining the loop resistance of a power supply network with a neutral conductor (called N), a phase or external conductor (called L1), a ground or protective earth conductor (called PE), and a fault current breaker (called FI) based on the differential quotient Ri=dU/dI≈(U1−U2)/(I1−I2); whereby U1 is the measured, unloaded network voltage, I1 is the zero current without load, U2 is the measured, loaded network voltage, and I2 is the calculated load current. According to one aspect of the invention, the following steps are provided: Loading of a L1-N loop and determining the resistance RL1 according to equation (1), loading of a N-PE loop with a measuring current IM under a measuring voltage UM which is small enough to avoid triggering of the fault current circuit breaker, and determining the resistance RPE according to the following equation (2): RPE=UM/IM  (2) and determining the loop resistance as RL1+RPE.

Abstract: In a first measurement step, the two test probes of a measurement apparatus are contacted with two of the three phase lines. The measurement apparatus determines the frequency of the three-phase voltage. In a subsequent second measurement step, one of the two test probes is brought into connection with the remaining third phase line. The other test probe is held in contact with the other line. In the second measurement step the voltage level or voltage profile on the third phase line is evaluated inside the measurement apparatus in comparison to the first phase line during one or more time windows of length .pi..