My German residence is supplied with 3 phase. The "main" distribution panel, wherein the service feed is connected, supplies the "kitchen zone" hereafter zone A. From the main panel, a 5 conductor 10 mm^2 (3 phase) is connected to a secondary distribution panel. All 3 phases of this line are fused at 20 A in the main panel. In the secondary panel, this line is immediately connected to a Hager CDA440D. AFAIK, this is a Residual Current Device (RCD). Next are 16 A fuses for multiple zones in the secondary panel.
I recently purchased a basic 1500 W electric hot plate. Connecting it to any outlet supplied by the secondary panel trips the RCD*. It does not matter if the hot plate is set to Min or Max, it always immediately trips the RCD. Whereas zone A, which does not have a RCD, has no problem operating the hot plate under any setting.
Many high wattage devices have been operated from the secondary panel without this issue. 3000 W halogen work lights, 2000+ W drum sanders, etc. Big home renovation.
*Maybe the fuse too, I can't remember that part. Definitely the RCD tripping.
1) Can this behavior be explained?
2) Are there any errors in this situation to be corrected?
Thank you for the advice :)
P.S. I want to learn how this works. Please save yourself the time and effort of posting dogmatic replies, i.e. "call an electrician". In Germany, it is legal for uncertified individuals to perform some electrical maintenance.