Hi, The questions throughout this thread here concern what appears to be a ground-breaking video about PCB layout and EMC /Signal Integrity....This video smashes the "commonly held knowledge" on PCB layout...
(BTW, the video lags the audio on this video by about 15 seconds)
Connecting to earth solves noise/EMC problems?
This video, at 5:00 onwards, explains that connecting the chassis of an equipment to earth is absolutely nothing to do with improving EMC….
PCB video (about grounding)
I have actually had systems where a PCB was inside a class II plastic enclosure. The PCB comprised an offline, isolated SMPS. This PCB was fed by 240VAC Earth, line and mains.
The offline SMPS had to go in its own little metal latticed cage so that the system could pass radiated emissions.
The metal cage was inside a class II plastic enclosure, so therefore there was no safety reason to connect this little metal cage to earth.
However, the secondary side of the offline SMPS PCB, comprised USB connections etc from off-board, which have an earthed ground. As such, the entire secondary side ground needed to be connected to earth.
Due to this, the metal latticed cage also needed to be connected to earth...you simply couldn’t connect it to any other node, since if you did you would be violating the isolation requirement of the offline SMPS. As you know, Earth is the only thing that you can have on primary and secondary sides of an offline isolated SMPS. This is because if there is a fault to earth, then the fuse will blow, and thus offer protection like that.
The thing is, that in an offline isolated SMPS, the input common mode chokes, are all to do with filtering the common mode "real earth" return current. The input Y capacitors also connect to "real earth", and are equally concerned with filtering the common mode "real earth" current. So in fact, you DO need to connect enclosures to "real earth" ground for the purposes of EMC improvement after all. Would you agree? If the little metal enclosure in this situation described here, was not connected to "real earth", then the Y capacitors of the offline SMPS would also not be wanted to be connected to "real earth". Do you agree?
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Also 5:17 onwards of this video concludes that connection to earth DOES improve the EMC situation.....
Who do we believe?
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The reference to EMC on an aeroplane (at 6:00) is “incompletely_explained” in a way, because in an aeroplane, the aeorplane’s chassis (wings, fuselage etc) can be regarded to be “real earth”. Would you agree?
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I would tend to agree that connecting a metal chassis to earth generally has nothing to do with EMC improvement. However, supposing the equipment was in a controlled environment, such that connection to earth for safety reasons was not necessary…...then in that case, I believe that connecting the chassis to earth would give better EMC improvement, compared to eg, leaving the metal chassis floating...would you not agree?
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Also, I am not sure if I entirely agree that connection to earth is of no benefit for EMC reasons... Once I built a crystal set radio. It did not work. I then soldered a wire to the crystal set’s circuit ground, and connected this wire to the earth in a mains socket. The crystal radio immediately worked. It would not work when this earth connection was removed.