|

If the PCB is sealed with solid sealant, how to determine the creepage distance and clearance?

functional insulation as well as other insulation exists on circuit boards. Typically, the surface environment of a circuit board is determined to be either Pollution degree 3 or pollution degree 2.
If the circuit board is mounted in an electrical box and sealed with a solid sealant, the sealing will look as follows:

What should be the pollution degree of the functional insulation between the copper tracks on the PCB and between the energized parts on the component?
Here, the functional insulation is located inside the solid sealant and there is no contact between the path of the functional insulation and the outside air. According to the definition of electrical clearance, it can be assumed that there is no electrical clearance here. At the same time, the creepage distance is defined along the surface of the insulation, and obviously, there is no surface here either.
It may be argued that there is still a gap between the solid sealant and the PCB material, and that an clearance and creepage distance can be formed, but it is a pollution degree 1. This view is more conservative, because even if a gap is formed, it is not a continuous gap.
At the same time, the pictures show that this solid state sealant fills so well that it is essentially impossible to create a gap. The manufacturer also indicates that there is a vacuuming procedure prior to filling the solid state sealant. When we evaluate this type of structure, we can have some control over the material and specification of the solid state sealant, as well as some control over the filling process.
There may also be reinforced insulation internally, as there are isolation measures between the 220-240V circuit portion and the SELV circuit, which are judged by the same rules for clearance and creepage distances as functional insulation.

Similar Posts

  • |

    Clause 3 – How to understand the definition of “room temperature”

    room temperature: ambient temperature specified in the general conditions for the tests.Note 1 to entry: The ambient temperature is specified in 5.7. This item comes from standard IEC 60335-1:2020 edition 6.0. In commented version (CMV) of the official standard IEC 60335-1:2020 edition 6.0 allows the user to identify the changes made to the previous edition…

  • Clause 3 – How to understand the definition of “fixed appliance”

    fixed appliance: appliance that is intended to be used while fastened to a support or while secured in a specific location. The definition emphasizes fastening to a bracket or fixing in a specific position. Generally, we think that this kind of fixation requires some installation actions and some fixing devices, these devices can be fixed…

  • Clause 3 – How to understand the definition of “thermal cut-out”

    thermal-cut-out: device which during abnormal operation limits the temperature of the controlled part by automatically opening the circuit, or by reducing the current, and is constructed so that its setting cannot be altered by the user. There are three key provisions here. First, the thermal cut-out is a heat-sensing element, second, it can only be…

  • Clause 3 – How to understand the definition of “motor-operated appliance”

    motor-operated appliance: appliance incorporating motors but without any heating elementNote 1 to entry: Magnetically driven appliances are considered to be motor-operated appliances. Household electrical appliances usually use heating elements or motors to complete their designed functions. The main functions are heating, such as heating food or air, and rotation or mechanical movement of products, such…

  • Clause 3 – How to understand the definition of “user maintenance”

    user maintenance: any maintenance operation stated in the instructions for use, or marked on the appliance, that the user is intended to perform. Allowed user-executed operations, the operation guideline was given in user manual, and it could be showed in enclosure of appliance. Since it is a allowed user-executed operation, then additional protective method should…

  • 第3項 – 「安全特別低電圧」の定義の見方

    安全特別低電圧: 導体間および導体とアース間の電圧は 42 V を超えず、無負荷電圧は 50 V を超えない 安全特別低電圧が主電源から得られる場合、安全絶縁を介する必要があります。 注 1 指定された電圧制限は、安全絶縁変圧器が定格電圧で供給されるという前提に基づいています。注 2 安全特別低電圧は SELV とも呼ばれます。 はじめに-1 。また、本項で定義する「安全」は、SELV を使用者が直接触れることができる絶対的な安全を意味するものではありません。ユーザーは、セクション 8.1.4 の要件を満たす SELV 回路のみに触れることができます。この電圧は通常、安全絶縁変圧器または別の巻線を備えたコンバータを通じて電圧を降圧することによって得られます。通常、これは安全絶縁変圧器を通じて得られます。ここで、別個の巻線を備えた安全絶縁変圧器またはコンバータは、一次巻線と二次巻線が物理的に構造的に分離されていることを保証できます。つまり、一次巻線と二次巻線が直接接触しないようにすることができます。この別巻線による回路分離に対応した電圧調整方式の一般的な例は、220V 回路に抵抗とコンデンサを直列に並列接続する RC 降圧方式です。 RC降圧方式では、回路内で高圧部と低圧部が接続されます。明らかに、物理的手段によって回路を分離する前者の方法の方が安全です。単純な物理的分離である場合でも、安全要件を満たすことはできません。規格で要求される絶縁は二重絶縁または強化絶縁の要件を満たす必要があります。簡単に言うと、高電圧部分と低電圧部分の間に非常に単純な絶縁(低温耐性を持つ薄いプラスチックシートなど)がある場合、この絶縁は高温または高電圧条件下で破損しやすく、基本的には絶縁できません。このプラスチックシートの層は絶縁の役割を果たしますが、高電圧回路と低電圧回路を物理的に分離することもあります。二重絶縁と強化絶縁の絶縁要件も二重保護の手段です。下の図に示すように、トランスには一次巻線と二次巻線を分離するためにディスクに垂直に配置された 3 つのプラスチック ブラケットがあり (一次巻線と二次巻線の外側には青いプラスチック テープが巻かれています)、一次巻線と二次巻線は物理的に隔離されています。 下の図に示すように、トランスには中央の一次巻線と二次巻線に黄色いテープが巻かれています。強化絶縁の沿面距離要件を満たしているかどうかを確認するには、2 つの巻線間の黒いブラケットの沿面距離に特に注意を払う必要があります。そうでない場合、その変圧器は安全絶縁変圧器として判断できません。 安全絶縁トランスの構造については次回詳しく説明します。 As shown in the figure below, the transformer has yellow tape wrapped around the primary and secondary windings in the…