Mother board connection to the case

[priestnot]

Well first off I want to thank to the people that are going to take their time to answer my question.

I have a mini ITX computer that I am tring to fit into a wall, so I made a special metal structure.

But now I have a problem when i mount the mother board into the metal structure should i connect the motherboard ground to the metal structure?

I see two possible outcomes.
The first if i connect the ground to the metal enclosure i get more protection of EMF and EMI.
The second is if i insulate the ground from the case I will get a better protection if there are some sort of a short circuit to the case.

So what should I do?

 

[FoxyRick]

In every PC I've built (a lot!) the MB has always been grounded to the case by the fixing screws. I would say to ground it.

I did once have a short - a screw had slipped under the MB and I didn't notice. I smelled it a few seconds after powering up. It had managed to jam between the power input to the main regulator and the case, and was glowing bright orange! The MB was not damaged, amazingly.

 

[alexan_e]

Yes, all the PC I have ever owned had an IEC plug for the psu which connected the ground to the case.
I can't imagine having a metal box with a mains power supply that is not grounded, any kind of voltage leak towards the chassis could be dangerous.

The second is if i insulate the ground from the case I will get a better protection if there are some sort of a short circuit to the case.

I don't understand that , so if for any reason you have a short to the case you prefer to keep it that being protected by it?

 

[FvM]

You're addressing two different aspects, electrical safety and EMI.

Electrical safety is provided by the PSU, which exposes only SELV circuits. The safety of the PSU is however (partly) based on the mains input protective earth connection. Although not explicitely specified in the ATX and microATX design guides, all standard PSUs are connecting PE to case and also to secondary return COM. This already determines motherboard grounding in a usual design.

EMI-wise, the ATX specification demands a grounding of the IO shield, apparently assuming a metallic enclosure. This ground connection is essential to achieve the EMI attenuation expected by the motherboard design. Not connecting it makes all connected I/O cables act as radiating antennas. In so far EMI considerations effectively require a direct grounding of motherboard to enclosure.

 

[demetal]

Hi,

In most of the cpu's the screwing hole of the motherboard is connected to the ground of the motherboard circuit...

So if you are screwing it to cabin means it is connected to the main ground of the mains...

As the SMPS chasis is connected to mains ground -> which is connected to cabin -> which is connected to MB pcb's ground.

Concluding that its safer to ground the mother board. As its a default configuration on matter where you place it.

Thank you