Patent ID: RE44455

Claim:
A measuring array with an earth connection point for determining an insulation resistance (R iso ) of an energized electrical apparatus or of an installation including a supply voltage U B with a positive pole and a negative pole, the measuring array comprising: two switches (S 1 , S 2 ) or a corresponding two-way switch being provided for creating a current path between one of the two poles and said earth connection point in order to determine the insulation resistance (R iso ) generally obtained when one or a plurality of insulation faults occur at any potential reference; a current measuring system connected between the connection point of the two switches (S 1 , S 2 ) and the earth connection point; a microcontroller configured for determining the insulation resistance by performing two measurements one after the other, in which during the first of these two measurements, the first switch (S 1 ) is closed whilst the second switch (S 2 ) is open, and during the second of these measurements, the first switch (S 1 ) is open whilst the second switch (S 2 ) is closed; and said microcontroller is further configured for measuring a current between the connection point of the two switches (S 1 , S 2 ) and the earth connection point so that the currents measured at that point during the two measurements are used to calculate the insulation resistance (R iso ), wherein the insulation resistance (R iso ) is calculated from R iso =U B / (I PE -I PE ′)wherein I PE is the current measured with the current measuring system with switch S 1 Being closed and switch S 2 being open, and I PE ′ is the current measured with the current measuring system with switch S 2 being closed and switch S 1 being open.