Yes, a megger places voltage on the system. In England we typically test normal 240/415V systems at 500V DC.
It's a high voltage, but supplied through a high impedance so that the current is limited, typically 3 or 4mA into a dead short. The 500V level is achieved only if the circuit insulation is good.
I'd be looking for a value of at least 1 meg., although I'd rather let the wiring dry out some more and get it higher before re-applying power.
