EN
LVD Insulation Test
LVD insulation test: resistance in de-energised circuits, moisture-contamination diagnosis assessed against standard acceptance values, reported.
The LVD insulation test measures the resistance of the insulation between live conductors and earthed parts in low voltage equipment under a DC test voltage. The measurement shows numerically whether the insulation material has degraded through moisture, dust, thermal ageing or mechanical damage, and verifies the first stage of LVD safety. Being made on a de-energised circuit, it is planned during shutdown or before commissioning.
Method and Rules
- Test voltage: Chosen per nominal voltage (typically 500 V DC for circuits ≤500 V; manufacturer/standard value for separation windings). The megger's short-circuit current and accuracy are stated in the report.
- Measurement points: L-N, L-PE, N-PE; circuits measured separately on multi-motor-drive units. Electronic cards, PLCs and drives are disconnected before test, or short-circuited per manufacturer instruction, to protect them from the test voltage.
- Duration and stabilisation: The reading is taken after the polarisation effect settles (typically 15-60 s constant wait); the simplified PI/DAR logic also applies to small equipment.
- Acceptance: Varying by standard and manufacturer, the practical general floor is 1 MΩ; machine electrics per TS EN 60204-1 may demand higher. Trend matters more than absolute value.
Interpretation and Next Step
Low insulation resistance alone is not a failure: in humid areas (painting, washing, cold stores) readings can be low in winter and high in summer. Ambient temperature-humidity are therefore noted and comparison is reduced to the same condition. If a moisture-driven drop recovers after drying-cleaning the issue is surface; if it does not, permanent insulation damage, cable crush or a water path is investigated. Testing the instrument against its own calibration resistors right after the reading proves the measurement's credibility. If the result is normal yet the equipment reports heating, the insulation test is insufficient alone; the chain closes with the leakage voltage test and thermography.
Legislation and Outcome
The test sits in the periodic electrical programme under Law No. 6331, the Work Equipment and Internal Electrical Installations Regulations. References are TS EN 60204-1, IEC 61557-2 and product standards. The protocol is signed with equipment identity, test voltage, ambient conditions, device serial/calibration data and readings; non-compliances carry insulation remediation and retest proposals. This test is an element of our PL Analysis and LVD Tests set; for the other steps see High Voltage and Earth Continuity, or contact us for your programme.
FAQ on LVD Insulation Test
It measures the insulation resistance in megaohms, i.e. how many mA pass through the insulation barrier under a DC test voltage (typically 500 V; higher for main insulation) for shock protection. The measurement is applied between body and live parts with supply-active connections detached; the protective earth (PE) path is verified separately. The result is compared with the nominal voltage-insulation class reference limit (e.g. a 1 Mohm floor, far higher for sensitive circuits).
Design-production follows the insulation resistance rules of TS EN 60204-1 (machines) and TS EN 61439 (panels); the periodic operating test carries the IEC 62353 / relevant product standard logic. Limits vary with test voltage and insulation type (basic-functional-reinforced); humidity-temperature of the measurement environment demands reference correction. The interpretation reads the trend against past measurements and the degradation speed, not a single number; a suspect low value is clarified by re-measurement-drying-isolation.
The device must be de-energised and discharged; electronic sections like PLC-servo-touch must be protected per the connection-disconnection guide. Temporary on-site groundings are removed; charged supply capacitors are discharged. Measurement points-schematic mapping-identity label are prepared; afterwards the permanent-shield-correct re-connection check and function test are done. Procedure-noncompliant connection is the most frequent cause of either electronics damage or misleading readout.
Insulation resistance below limit; phase-phase, phase-earth, neutral-earth deviation; instability during measurement (moisture-contamination-surface leakage), drop in repeat measurement; discovery of insulation damage-carbonisation-tracking marks. Removal: surface cleaning-drying, faulty cable-element change, barrier renewal; then a verification retest. The report gives temperature-humidity-method-voltage values; a failed circuit cannot pass serial-CE-periodic approval unless repaired-verified, and it is followed in the inventory with the fault record.