Why do inductors also have safety distance requirements?

Original: Light of Devices

The basic function of inductance in circuits is filtering, mainly for signal processing. Why are there safety distance requirements when doing certification? This article will provide relevant answers to this question.

In fact, for general circuits, there is no clear requirement for the safety distance of inductors. They only need to meet the basic voltage insulation requirements, and the product will not short circuit after long-term operation.
When testing inductors, we often test the voltage resistance of windings to windings or windings to magnetic cores, usually around 500VAC.

However, if inductors are applied in high-voltage circuit scenarios, it will be different. In high-voltage circuits, the spacing between inductor pins often needs to comply with electrical clearance and creepage distance standards to avoid short circuits or discharges.
According to the IEC60950 standard, different voltage levels correspond to different minimum distances. When the 400V voltage circuit is not slotted, the electrical gap between the inductor pins must be ≥ 6.4mm.

In terms of creepage distance, for 220V circuits, the creepage distance of FR4 substrate needs to be ≥ 4.0mm. For high-voltage inductors, such as those next to the main transformer of a switching power supply, a reinforced insulation distance of ≥ 8.0mm is required.
When the working temperature of the inductor is relatively high, the safety distance can be appropriately increased to compensate for the aging of the insulation material caused by long-term use of the inductor.

In the process of circuit design, if the creepage distance is insufficient, slotting can also be used to meet the requirements. For the selection of inductor materials, it is necessary to use fire-resistant and flame-retardant skeleton, high-temperature resistant enameled wire, and safety certified insulation tape to ensure compliance with safety standards and requirements.
Overall, the safety distance requirement for inductors is essentially to prevent safety hazards caused by electrical breakdown, leakage, and insulation failure. This can refer to standards such as IEC 60950 and UL 60950, and be designed comprehensively based on voltage levels, working environments, and material characteristics to ensure testing and certification pass.