EMC vs Isolation

Thread Starter


Joined Sep 22, 2021
Hi to all,
I'm desigining a PCB with an Eurocard size that will be used in a subrack.
The board is connected to a mother board internal to the subrack and have some connector on the frontal side.
On the frontal side, the boards are covered by a metal front panel (chassis) that will be connected to earth.
In order to respect some safety standard I have to ensure 1500Vac of isolation between chassis and every signal provided by each frontal connector (also ethernet).
In my case I have a Single Board Computer that shows its ethernet connector on the front panel, and as you know, every computer realizes an electrical connection between its GND and chassis (metal enclosure of ethernet connector in my case).
Moreover I need to isolate some signals coming out from a DB37 connector as shown in the picture. The DB connector realizes an electrical connection between itself and chassis.
So I think I have the following problems.
1) due to electrical connection between gnd signal of Single Board Computer and chassis, I cannot ensure the 1500Vac isolation at ethernet connector.
2) My "gnd signal" is connected the "gnd field" via chassis and this defeats the electrical insulation between "gnd signal" and "gnd field".
Any suggestions?

Finally, to ensure the 1500Vac isolation I cannot connect the chassis to any gnd signal on board. I will connect chassis to an equipotential bar in the cabinet and this could keep me safe from any noise. Is it correct?
Thank you for your precious support.


Deleted member 115935

Joined Dec 31, 1969
Your in for a world of pain here.

First up, what standards are you testing to / meeting ?

e.g. some standards require that the front panels is connected to "safety" earth , others insist its not.

The standards will guide you as to what is best practice.

EMC is about radiating. Either you radiating out, or something outside radiating in and affecting your circuit.
At a basic level , will you radiate to cause interference to something else, when zapped by an ESD , will you stop working.

On the basis of your question , I am guessing your new to this.

This I find is a good site to refer back to


Specific thoughts

Check the DB37 connector is rated for your stress voltage ?

Ethernet, is typically transformer isolated , which provides the ESD / isolation. Look at the layout rules for the chips your using as a guide. Especially on planes under the tracks between the transformer and the connector. The metal around the edge of most Ethernet sockets, connects to the chaise ground, which is typically the safety ground,

What is the aim of your signal isolation block ?

Thread Starter


Joined Sep 22, 2021
Hi andrewmm,
thank you for your answer.
The standard is EN50155 and so far I cannot find nothing about chassis connection.
I know that the islation test is carried out between all the IO signal together and the chassis.
The DB37 is good for this application.
Thank you for the suggestion about the isolated ethernet signal and for the website.


Joined Oct 13, 2021
Electromagnetic Compatibility (EMC) and Radio Frequency (RF) Testing. Electromagnetic Compatibility, also known as EMC, is the interaction of electrical and electronic equipment with its electromagnetic environment, and with other equipment. All electronic devices have the potential to emit electromagnetic fields.