cannot limit the inrush current unless it cools for more than 1 minute to get a higher resistance. Another disadvantage is that the NTC thermistor is not short-circuit-proof. Another way to avoid the transformer inrush current is a "transformer switching relay". This does not need time for cool down. It can also deal with power-line half-wave voltage dips and is short-circuit-proof. This technique is important for IEC 61000-4-11 tests. Another option, particularly for high-voltage circuits, is to use a pre-charge circuit. The circuit would support a current-limited precharge mode during the charging of capacitors and then switch to an unlimited mode for normal operation when the voltage on the load is 90% of full charge. Switch-off spike When a transformer, electric motor, electromagnet, or other inductive load is switched off, the inductor increases the voltage across the switch or breaker and cause extended arcing. When a transformer is switched off on its primary side, inductive kick produces a voltage spike on the secondary that can damage insulation and connected loads. See also Ripple (electrical) References External link IEC 61000–4–30, Electromagnetic Compatibility (EMC) – Testing and measurement techniques – Power quality measurement methods, Published by The International Electrotechnical Commission, 2003. Electrical parameters