Radiated EMC test with chassis earthed or chassis floating?

[waveboy]

Supposing we take the following set-up to a Radiated EMC test chamber (30MHz – 1GHz)…

We have a 12V battery in a totally enclosed metal enclosure X. A cable from this battery leaves this enclosure and feeds into another metal enclosure, Y, which is semi open, since its front panel is absent.
Enclosure Y contains a 10W buck converter battery charger, which charges a battery also in the same enclosure Y.

Which would give the best radiated EMC performance?.(least radiated emissions)....

1…Doing the radiated EMC test with Enclosure X’s chassis connected to earth ground, and enclosure Y’s chassis connected to Enclosure X’s chassis?
2….Doing the radiated EMC test with both chassis’s floating (not connected to earth ground)?

 

[zappedagain]

The answers is "it depends..."

If Enclosure A is 'totally enclosed', how do the wires exit? Via filter caps? A shielded cable? If neither of those your cabling is probably going to be a strong antenna that will swamp any other issues. With proper filtering on the PCBAs or maybe the cables you might get lucky.

If your cable is shielded and properly tied to Enclosure Y then you could have a nice Faraday Cage that only has an opening for EMC at the absent front panel. 'Properly tied together' means 1 or 2 won't matter.

This is my go-to literature if you want to learn more about this -

https://www.emiguru.com/books/edn-designers-guide-paypal/

Z