Powder Coating Suitability for Earthing

[turbodudet]

I work for a company that uses many HX750W powersupplies in 19 inch rack systems that we supply and I am tasked with tracking down the source of some electrical noise on USB 5v that we are experiencing.

It is my understanding that a computer chassis is supposed to be earthed for noise immunity and this is generally accomplished because the powersupply chassis (which is internally earthed) is in contact with the computer chassis (metal to metal and via screws). Because your Corsair power supply (eg HX750W) is powdercoated the computer chassis is not getting properly earthed (to the buildings earth/ground connection). I have confirmed that this is the case across multiple corsair powered PC’s using a multimeter and the resistance between PC chassis and earth varies widely depending on how much incidental contact there is.

I understand that the 0VDC of the powersupply is connected internally to earth (nearly 0 ohms using a multimeter) and the PC chassis may get some connection via the motherboard and USB connectors etc but this is not the same as properly earthing the PC chassis.

 

Can anyone comment on the suitability of powdercoating powersupplies with respect to the above comments because I am currently having to assess whether they are suitable for our future systems.

[RAM GUY]

With current ATX 2.X designs the Ground is floating on the MB and can be at any number of points within the system at any time. However the grounding for the PSU is done through the ground in the power cable and why it can be important that one use a properly grounded outlet and surge protector for the system to operate properly. Failure to do can cause any number of anomalies like a wine or buzz at odd times to it not operating properly under certain soft off power schemes. The case on your system should have a natural ground from the connections to the MB and thus grounded back through the Ground connections on the power cable from the PSU to Mother board and since they are floating in the system it is not as important that the case it self be grounded to earth ground.