High voltage to low voltage conversion from multiple channels
If you don't want a continuous current draw (and an average that is only in the region of a few microamps) then consider using a low leakage analogue switch to sample the line voltage and charge a small capacitor up via a resistor. The resistor and capacitor form a potential divider and the capacitor voltage charges up to a voltage that is dependant on line voltage, resistance of the resistor, capacitance and length of time the switch closes for.

After a measurement is made, the capacitor can be discharged by a MOSFET or another analogue switch and the next line measured in the same way by using the analogue switch connected to its line: -







simulate this circuit &ndash; Schematic created using CircuitLab

The rate that the capacitor charges is exponential and if the line voltage is (say) 30V and CR is 1n x 1M (= 1msec) then you'll want to keep the line sense switch closed for only a fraction of that time to ensure that the ADC input does not hit the 5V limit imposed by the zener protection diode.

I calculate that for 3V across the capacitor. the switch needs to be activated for 105.4 usecs (see this calculator).

Of course you may be able to get away with a simple potential divider in place of the R and C above but your question is a bit unclear about what is and isn't acceptable. Using a potential divider that scans all the inputs via analogue switches should be OK I believe in your application.