Good to know Testing the Safety of Electrical Installation Find out more about testing safety of electrical installations According to European standards requirements electrical installation safety testing includes a combination of following tests: • Insulation resistance, • Continuity of protective conductors and equipotential bonding, • RCD testing, • Line and fault loop impedance, • Earth resistance testing (two-wire method without probes, three / four-wire method with two probes, method with current clamp and two probes, method with two current clamps) • Specific earth resistance, • Phase sequence, voltage and frequency. These tests are performed in order to ensure that the requirements are met for the protection of persons, livestock and property against the risk of electric shock and to ensure that the automatic disconnection of the supply is performed correctly. Insulation resistance The insulation is intended to prevent any contact with live parts and withstanding mechanical, chemical, electrical and thermal stresses. Insulation test discloses insulation faults caused by pollution, moisture, deterioration of insulation materials etc. Insulation resistance measurement is covered by the IEC / EN 61557-2 standard. The power must be switched off and the installation must be disconnected before performing this test to ensure that the test voltage will not be applied to other equipment electrically connected to the circuit to be tested, particularly devices sensitive to voltage surges. Insulation resistance shall be measured between: • Line conductors, • Line and PE conductors, • Line and Neutral conductors, • Neutral and PE conductors.
Test circuit for insulation resistance measurement
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Test circuit for insulation resistance measurement
The insulation resistance test is performed with a DC voltage on a dead system and the resistance must be above the minimum limit set out in the appropriate standards and regulations. Limit values for electrical installations acc. to IEC 60364-6: Rated voltage of circuit (V)
DC test voltage (V)
Insulation resistance (MΩ)
LV secondary switchboard or LV 250 main switchboard
≥0.5
Less than or equal to 500 V 500 including LV main switchboard
≥1.0
Greater
≥1.0
1.000
METREL’s hint: EurotestAT and EurotestXA have built-in the “Insulation ALL” function which enables performing of 3-port insulation test (L-N, L-PE, N-PE or L1-L2, L1-L3, L2-L3) in one step. This is a very time saving feature especially if measuring insulation on outlets. Continuity of protective conductors and equipotential bonding The purpose of continuity measurement is to check the continuity of the protective conductors, the main and supplementary equipotential bonds. The test is carried out using a measurement instrument capable of generating a no-load voltage of 4 to 24 V (DC or AC) with a minimal current of 200 mA.
Test circuit for continuity R200 mA measurement
Test circuit for continuous resistance measurement
RCD testing RCD devices are used as protection against dangerous fault voltages and fault currents. Various test and measurements are required for verification of RCDs in RCD protected installations. Measurements are based on the EN 61557-6 standard. Scope of RCD test is: • to verify effectiveness and proper operation of the RCDs; • to verify disconnection times and trip out currents of RCDs; • to verify that there are no or limited present fault currents in the installation. The following measurements and tests of RCDs can be performed: • Contact voltage, • Trip-out time, • Trip-out current, • RCD autotest.
Continuity test is covered by the EN 61557-4 standard. The measured resistance must be lower than a threshold specified by the standard applicable to the installation tested, which is usually 2 Ω. As the resistance value is low, the resistance of the measurement leads must be compensated, particularly if very long leads are used. METREL’s hint: EurotestAT and EurotestXA can perform the N – PE loop test between instrument’s N and PE test terminals. This makes testing with the plug test cable on outlets possible.
Accessories 1.61
Circuit for testing RCD
METREL’s hint: METREL installation testers have built-in the “RCD AUTO” function which performs RCD testing at x1/2, x1 and x5 current multipliers at both 0° and 180° automatically. With this function all relevant RCD tests can be carried out in one step which is very simple and time saving feature.
