Re: Purpose of parallel combination R & C is used between Chassis and Circuit ground
It's there to leak away any charge that has built up between chassis and real ground without allowing enough conduction that it could pass lethal current. The capacitor is to offer lower impedance to high frequencies. Usually you see this circuit between primary and secondary sides of switch mode PSUs. The resistor value isn't critical, if you make it too low the current might reach danger level and if you make it too high it may not conduct leakage away sufficiently. 10M is probably a risky value, I would suggest you use 4M7 or lower. Note the voltage rating of the capacitor, the resistor should also be rated for high voltage, most small axial resistors are only rated to 250V,
Brian.