Document ID: chunk:federal_register_of_legislation:F2023L01526:body:0:p39
Version: federal_register_of_legislation:F2023L01526
Segment Type: other
Provision Reference: 
Character Range: 110502–113509

negative side of the high voltage bus and the electrical chassis (see Figure 2).

        Calculate the electrical isolation (Ri) according to the following formula:

        Ri = Ro*Ub*(1/U1' – 1/U1)

    Figure 2
    Measurement of U1'

        If U2 is greater than U1, insert a standard known resistance (Ro) between the positive side of the high voltage bus and the electrical chassis. With Ro installed, measure the voltage (U2') between the positive side of the high voltage bus and the electrical chassis (see Figure 3). Calculate the electrical isolation (Ri) according to the formula shown. Divide this electrical isolation value (in Ω) by the nominal operating voltage of the high voltage bus (in volts).

        Calculate the electrical isolation (Ri) according to the following formula:

        Ri = Ro*Ub*(1/U2' – 1/U2)

    Figure 3
    Measurement of V2'

       2.2.3.5. Fifth step

        The electrical isolation value Ri (in Ω) divided by the working voltage of the high voltage bus (in volts) results in the isolation resistance (in Ω/V).

Note: The standard known resistance Ro (in Ω) should be the value of the minimum required isolation resistance (in Ω/V) multiplied by the working voltage of the vehicle plus/minus 20 per cent (in volts). Ro is not required to be precisely this value since the equations are valid for any Ro; however, a Ro value in this range should provide good resolution for the voltage measurements.
Annex 5B

Isolation resistance measurement method for component based tests of a REESS

       1. Measurement method

        The isolation resistance measurement shall be conducted by selecting an appropriate measurement method from among those listed in paragraphs 1.1. through 1.2. of this Annex, depending on the electrical charge of the live parts or the isolation resistance, etc.

        Megohmmeter or oscilloscope measurements are appropriate alternatives to the procedure described below for measuring isolation resistance. In this case, it may be necessary to deactivate the on-board isolation resistance monitoring system.

        The range of the electrical circuit to be measured shall be clarified in advance, using electrical circuit diagrams, etc. If the high voltage buses are galvanically isolated from each other, isolation resistance shall be measured for each electrical circuit.

        If the operating voltage of the Tested-Device (Ub, Figure 1) cannot be measured (e.g. due to disconnection of the electric circuit caused by main contactors or fuse operation) the test may be performed with a modified test device to allow measurement of the internal voltages (upstream the main contactors).

        Moreover, modification necessary for measuring the isolation resistance may be carried out, such as removal of the cover in order to reach the live parts, drawing of measurement lines, change in software, etc.

        In cases where the measured values are not stable due to the operation of the isolation resistance