Where to place an EMI filter

[PinheadBE]

Hi,

I have a high power (5 V - 40 A) SMPS powering several almost identical modules.   Those modules each contain an µC and are connected through an I2C bus to another module who supervises the whole thing.

I would like to play it safe and add one or more EMI filters on the DC lines.
There is a distance between 1 and 2 meters between each module and the SMPS.

Where should I place the EMI filters ?  Close to the SMPS or close to the modules ?

Thanks.

[Phil1977]

Standard answer: It depends 

Do your modules backfire EMI to the power lines? Then I´d place the filters close to the modules.
Do you want "cleaner" power from the SMPS? Then place the filters near the SMPS...

Is the system connected to PE? Then it may be a good idea to keep all components connected with low impedance to PE and place filters where ground loops are created.

[PinheadBE]

Thanks Phil 

It is indeed to clean the power from the SMPS

Unfortunately, it's an older house where PE is only installed in rooms where water is present: kitchen, bathroom....
So, no PE in the living room where this project will be installed