Connect isolated ground to Earth?

  • #1
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I am currently working on a high power class E amplifier which will sit inside a metal enclosure. It is powered by two power supplies - both are isolated but one of the power supplies is mounted in the same enclosure. The power supply itself is in a metal case and that case is connected to 'earth'. So, through one of the PSU chassis, the entire metal enclosure of my project is connected to earth.

I have read that people connect common ground to their chassis because this helps prevent emission of electromagnetic waves due to the operation of the circuit inside the enclosure. More importantly (in my case) doing this helps to prevent interference from outside sources and noise on any input signals.

My question is: Should I connect the isolated common ground to the project enclosure (and hence also connect the isolated common ground to earth)? I have drawn a quick diagram of my circumstances where the blue dashed line represents the new wire that I am thinking of connecting between earth and isolated ground.

upload_2018-10-7_17-4-11.png


Thanks.
 

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  • #2
FactChecker
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Just remember that there is resistance in the earth and it can create potential differences between two grounds to earth. That can cause "ground loops". A good metal conductor between two grounds to earth and differential signals are often necessary.
 
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  • #3
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Just remember that there is resistance in the earth and it can create potential differences between two grounds to earth. That can cause "ground loops". A good metal conductor between two grounds to earth and differential signals are often necessary.
Thats a good point. Aside from that, does that system look to be ok if I connect the isolated ground to the chassis and earth?
 
  • #4
Tom.G
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Often keeping them isolated is a better bet, but not always. It depends a lot on the details of the particular installation; some of which you have little control over.

Try it both ways and use whichever has the least noise problem.

A third possibility is to connect the electronics ground to chassis with a capacitor, 0.01μF to 0.1μF.

For power supply noise getting into the amplifier, also try 0.01μF to 0.1μF across the power supply output leads, and/or from the supply "+" to chassis (use short leads at the power supplies).

If using capacitors, use short leads on them; longer leads reduce effectiveness at higher frequencies.

Cheers,
Tom
 

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