Bartosz,

relevant EMI is often caused by big inrush currents. Think of big lamps for a light show or heavy inductive loads like big mains transformers.


If big lamps must be driven, zero-crossing switching is not enough, because time constant of PTC mechanism of lamp is in the range of half cycle duration of mains frequency. So, lamps are pre-heated by applying short duration spikes with little amplitude (zero-crossing switching!). These little spikes are enough to increase lamp resistance, but too little to make them shine visibly.

Big ring core mains transformers can show extreme inrush currents. Such loads are switched-on in two steps: First, mains voltage is applied via a special NTC, which limits inrush current to a save level. Then, after about one second, NTC is short circuited, so that full mains voltage becomes connected to transformer.
Keep in mind, that transformers will not profit from zero-crossing switching!!

Kai