EMC Question of the Week: December 13, 2021

clump of dirt with a tree growing in it floating in space

Electrical products and systems with floating grounds are generally   

  1. unsafe
  2. unlikely to meet radiated emissions requirements
  3. all of the above
  4. none of the above


The best answer is “d.” The term "floating ground" generally refers to a circuit or system ground that does not make a connection to the earth. For example, the grounds of battery-powered devices, aircraft-in-flight and most automobiles. There is nothing inherently "unsafe" about a floating ground. In situations where the product relies on an earth ground for safe operation, the absence of that ground can certainly present a safety hazard. On the other hand, many products (for example, low-voltage devices powered through an isolation transformer) intentionally float the ground in order to make the product safer. 

The presence or absence of an earth ground rarely has any significant impact on radiated emissions. In general, the process of designing a product to meet radiated emission requirements is neither helped nor hindered by an earth ground connection. 

Note: Occasionally, the term "floating ground" is used to refer to a signal current-return that is isolated from a product's ground structure. This usage improperly confuses the concepts of ground and current-return and should probably be discouraged. Nevertheless, even in this context, a floating ground is not always unsafe and not always something that would make a product "unlikely to meet radiated emissions requirements."

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