Electronics > Beginners

Equipment Shielding

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Rigolon:
Hey guys,

A friend of mine has a product that the case is steel (which on of the objectives is to shield the circuit) and it goes on top of a wooden structure. He is going through a homologation process and there is a test where they touch the body (steel case) with 4kV (Guess to test the protection against ESD). He asked me if grounding the case he wouldn't have a problem.

In my opinion, as long it's a good grounding it won't be a problem. But where it should be grounded? In the mains earth or the ground of the circuit is fine?

I do believe that the correct one should be the mains earth, but where we live, most houses and buildings don't have a good grounding system or, even, don't have one at all.
So is there any problem using the circuit ground?

PS: The circuit works fine, it's just that for him to sell it to this client it has to go through this testings.

noname4me:
My experience is that it is passed to the main earth conductor (chassis ground) with the lowest impedance possible

The idea I think is that it is passed to ground without affecting the ground of the circuit where it can cause stuff like random button press event (for e.g.) or other artefacts.

There should be some inductance between the circuit ground and the chassis ground so that the ESD event does not enter the circuit.

I'm not an expert so please take this advice with a sackful of salt.

Sent from my SM-N960F using Tapatalk

JustMeHere:
GND can very well be isolated.   It's just a reference point and not necessarily connected to earth.

Also, at least in USA, earth gnd does not have to be as big as the rest of the wires, so it's not a good idea to send current through it on purpose.   It's job is to trip the breaker.

magic:
If the circuit is sensitive to electrostatic field (high impedance nodes, low noise, that kind of things) then it may be necessary to keep the chassis at the same potential as circuit GND.

For example, if circuit GND is connected to some ungrounded external cable/device picking up 50Hz mains noise and the chassis is earthed, 50Hz noise may appear in the circuit.

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