Document ID: chunk:federal_register_of_legislation:F2025L00028:reg:3:p9
Version: federal_register_of_legislation:F2025L00028
Segment Type: reg
Provision Reference: reg 3 (pt 9/11)
Character Range: 143846–147128

electrical chassis remains unchanged.

               These modifications shall not influence the test results.

               Utmost care shall be exercised to avoid short circuit and electric shock since this confirmation might require direct operations of the high-voltage circuit.

              5.2.1. Measurement method using DC voltage from external sources.

              5.2.1.1. Measurement instrument.

               An isolation resistance test instrument capable of applying a DC voltage higher than the working voltage of the high voltage bus shall be used.

              5.2.1.2. Measurement method.

               An isolation resistance test instrument is connected between the live parts and the electrical chassis. The isolation resistance is subsequently measured by applying a DC voltage at least half of the working voltage of the high voltage bus.

               If the system has several voltage ranges (e.g. because of boost converter) in conductively connected circuit and some of the components cannot withstand the working voltage of the entire circuit, the isolation resistance between those components and the electrical chassis can be measured separately by applying at least half of their own working voltage with those components disconnected.

              5.2.2. Measurement method using the vehicle's own REESS as DC voltage source.

              5.2.2.1. Test vehicle conditions.

               The high voltage-bus is energized by the vehicle's own REESS and/or energy conversion system and the voltage level of the REESS and/or energy conversion system throughout the test shall be at least the nominal operating voltage as specified by the vehicle manufacturer.

              5.2.2.2. Measurement instrument.

               The voltmeter used in this test shall measure DC values and have an internal resistance of at least 10 MΩ.

              5.2.2.3. Measurement method.

              5.2.2.3.1. First step.

               The voltage is measured as shown in Figure 1 and the high voltage bus voltage (Ub) is recorded. Ub shall be equal to or greater than the nominal operating voltage of the REESS and/or energy conversion system as specified by the vehicle manufacturer.

              5.2.2.3.2. Second step.

               The voltage (U1) between the negative side of the high voltage bus and the electrical chassis is measured and recorded (see Figure 1).

              5.2.2.3.3. Third step.

               The voltage (U2) between the positive side of the high voltage bus and the electrical chassis is measured and recorded (see Figure 1).

              5.2.2.3.4. Fourth step.

               If U1 is greater than or equal to U2, a standard known resistance (Ro) is inserted between the negative side of the high voltage bus and the electrical chassis. With Ro installed, the voltage (U1') between the negative side of the high voltage bus and the electrical chassis is measured (see Figure 5).

               The electrical isolation (Ri) is calculated according to the following formula:

              Ri = Ro*Ub*(1/U1' – 1/U1)

         Figure 5
         Measurement of U1'

              If U2 is greater than U1, insert a standard known resistance (Ro) between the positive side of the high voltage bus