No problem QQ. Actually normally charge doesn't penetrate within, though it's possible to create a capacitor configuration with interior surface of cage forming an outer conductor. But regardless the net charge within cage is still zero. Faraday cage works to block incident radiation as well as electrostatic fields Just on reason for grounding a FC: Mainly to protect from external shocks I think. While internally everything is at an equipotential, under AC induced field situation a floating FC could have large fluctuating voltages referenced to ground and that could entail sizable capacitive 'charging' currents between cage and ground. An earthing strap holds FC at ground potential. It's important to remember that a FC is only effective at frequencies where wavelength is much larger than mesh spacing.