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Electrical Measurements Guide
Document version: 1.0
Document date: 9. 8. 2022
Table of Contents
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1. Performing Electrical Measurements
Electrical measurements must be performed by licensed electrician and must be in accordance with requirements set in national legislation. In this document only information on specifics of some of the electrical measurements is given.
2. Earthing Conductor Continuity test
Continuity measurement should be performed for protective conductors, including conductors in the main and additional equipotential. Measurement will have to be made between PE terminal of charging station’s socket and inlet PE conductor. If the charging station is equipped with cable, the measurement should be made between PE conductor of the cable plug and inlet PE conductor.
WARNING!
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Before carrying out the measurements, switch off the charging station or main power supply. |
Continuity measurement should be made with a current greater than or equal to 200 mA. The open circuit test voltage should be between 4 and 24V (AC or DC). The measuring range shall include values 0,2 Ω to 2 Ω and the maximum percentage operating uncertainty within this measuring range shall not exceed +- 30 %. The resolution of digital equipment shall be at least 0.1 Ω.
The use of instrument, with option of measuring at higher current than 200 mA increases the accuracy of the measurement. The method of measurement is shown in the figure:
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Figure 1: Continuity measurement
Continuity of the wire is considered to be met if the connection resistance does not exceed the value of 2 Ω.
3. Insulation Resistance Measurement
Measurements of the insulation resistance of electric cables are performed between active conductors and between active conductors and the protective conductor connected to the earthing system.
Insulation resistance, measured at a test voltage of 250 V d. c. is satisfactory if its value is not less than 1 MΩ.
Table 1: Insulation resistance measurement conditions
Nominal voltage | Test voltage | Insulation resistance |
230/400 V, up to 500 V (Applicable to all charging station from Etrel) | 250 V d. c. | ≥ 1 MΩ |
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Because the charging station has varistors installed, they may affect the measurement result or may be damaged. the test voltage for this circuit should be SET to 250 V DC. the measured insulation resistance should be at least 1 MΩ. To perform the insulation resistance test, the power supply must be disconnected. |
Explanation:
Please follow the procedure as stated in the standard IEC 60364-6, which is stating that all current-using equipment must be disconnected before the test of insulation resistance, Chapter 6.4.3.3. To perform the insulation resistance test, the power supply must be disconnected.
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The standard values of insulation resistance measurement, shown in the table below are not applicable.
Table 2: Standard values of insulation resistance measurement are not applicable
Nominal voltage [V] | Test voltage d. c. [V] | Insulation resistance [MΩ] |
SELV and PELV | 250 | 0,5 |
Up to 500 V including FELV | 500 | 1 |
Above 500 V | 1000 | 1 |
4. RCD Test
The effectiveness of the automatic disconnection of the power supply by RCD devices should be checked with the use of appropriate test equipment, confirming that the relevant requirements are met and considering the operating characteristics of the device. The effectiveness of the protection measure can be considered satisfied if the trip occurs at a certain value of the leakage current and within a certain time.
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The effectiveness of the protection measure can be considered satisfied if the trip occurs at a certain value of the leakage current and within a certain time.
Table 3: Type AC and A residual current circuit breakers without built-in overcurrent protection - normalized switching time values
Normalized tripping time values for residual current IΔn | ||||
RCD Type A | Testing current | IΔn | 2 IΔn | ≥ 5 IΔn |
General purpose | Maximum tripping times | 0.3 s | 0.15 s | 0.04 s |
Table 4: Type B RCDs - normalized tripping time values for residual currents in rectifier circuits and for smoothed residual current
Normalized tripping time values for residual current IΔn | ||||
RCD Type B | Testing current | 2 IΔn | 4 IΔn | ≥ 10 IΔn |
General purpose | Maximum tripping times | 0.3 s | 0.15 s | 0.04 s |
5. Effectiveness of the Protection Against Electric Shock
In the case of TN systems, the effectiveness of protective measures in the event of damage by tripping the power supply is checked by:
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ZS is the fault loop impedance,
Ia is a current that causes an automatic power cut-off within the time specified in the table below,
Uo is the rated AC or DC voltage with respect to earth.
Table 5: Maximum switch-off times
| 120 V < Uo ≤ 230V | 230 V < Uo ≤ 400V |
AC | AC | |
TN | 0,4 s | 0,2 s |
TT | 0,2 s | 0,07 s |
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In TN systems, for distribution circuits and circuits with a rated current above 32 A, the permissible maximum time of switching off is 5 s.
6. Earth Electrode Resistance Measurement
Measuring of the resistance of an earth electrode shall be made by an appropriate method. Various methods exist and none of them is ideal, as they all have advantages and disadvantages. The methods, described below, are proposed in standard IEC 60364-6.
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An example is a method of measurement using two auxiliary earth electrodes, Method C1. Where the location of the installation is such that it is not possible in practice to provide the two auxiliary earth electrodes, measurement of the earth fault loop impedance according to Methods C2 or C3 will give an acceptable approximate value.
Measurement of earth electrode resistance using an earth electrode test instrument (Method C1)
An alternating current of a steady value is passed between the disconnected earth electrode, E, and a temporary auxiliary earth electrode, H, placed at a distance from E such that the resistance areas of the two electrodes do not overlap.
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RH Temporary auxiliary probe earth electrode resistance (current)
Figure 2. Measurements of the earth electrode resistance
Measurement of earth electrode resistance using a fault loop impedance test instrument (Method C2)
Measurement of the earth fault loop impedance at the origin of the electrical installation may be carried out with a test instrument according to IEC 61557-3.
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It is important that the earthing conductor is reconnected to the MET of the installation before the supply is reinstated.
Earthing conductor temporarily disconnected from the main earthing terminal (MET).
Figure 3. Measurement of the earth electrode resistance using an earth fault loop impedance test instrument
Measurement of earth electrode resistance using current clamps (Method C3)
With reference to the following figure the first clamp induces a measuring voltage U into the loop, the second clamp measures the current I within the loop. The loop resistance is calculated by dividing the voltage U by the current I.
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To avoid possible risks due to currents caused by potential differences between neutral and earth, the system should be switched off during connection and disconnection. It should be noted that the values of resistance obtained using Method C3 will typically be higher than those obtained using Method C1 because of the earth loop measurement.
Figure 4. Measurement of earth electrode resistance using current clamps
2-point (dead earth) method
In areas where driving ground rods may be impractical, the two-point method can be used. With this method, the resistance of two electrodes in a series is measured by connecting the P1 and C1 terminals to the ground electrode under test; P2 and C2 connect to a separate all-metallic grounding point (like a water pipe or building steel).
The dead earth method is the simplest way to obtain a ground resistance reading but is not as accurate as the three-point method and should only be used as a last resort, it is most effective for quickly testing the connections and conductors between connection points.
7. CONTACT INFORMATION
Technical support department
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