EMC Question of the Week: May 13, 2024
To meet radiated emissions requirements, a product that plugs into a wall outlet should ensure that the outlet's earth ground is well-connected to the
- circuit board ground
- frame ground
- both of the above
- none of the above
Answer
The best answer is “d.” The connection to the earth plays no role in meeting radiated emissions requirements. For safety reasons, many products require a connection from the frame ground to the earth ground terminal in the wall outlet. However, if this connection were missing, it would have virtually no effect on radiated emissions from the product. Double-insulated products, many low-voltage products, and products with their own GFCI (Ground Fault Circuit Interrupter) often have no intentional connection to earth ground. Designing these products to meet radiated emissions requirements is no more difficult than designing products with an earth ground.
While the connection to the earth is unimportant, grounding in general plays a critical role in meeting radiated emissions requirements. There can only be ONE high-frequency ground structure. Cables and large metal objects generally need to make a good high-frequency connection to this structure.
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