OK, I'm assuming that you need to know the presence or abcence of voltage. Industrially this is done using I/O modules. They could be mounted on a backplane or separate units. They require a logic suplly of 5, 15 or 24 V.
Here is just one link: **broken link removed**
Here is another such system: **broken link removed**
The modules are sometimes universal and available from many manufactures.
There are also quad modules availabe.
What we don't know is:
1. Are you interested in the presence/abcence of 240 VAC?
2. Is everything in one place?
3) How many points and locations?
You may have to provide interfcing from 5V logic to 3.3 V logic.