Separating Phase and Neutral in AC?
Without a ground wire

If I correctly understand the question, it's essentially like this:







simulate this circuit &ndash; Schematic created using CircuitLab

In this case, it is possible that only one of SW1 and SW2 are closed (because the timer may only interrupt one line).  The simple way to detect only the situation in which both lines are closed is to simply put a (safe!) load across the line and see if current flows.  A voltmeter, as shown, or neon lamp are both simple way to detect this situations.

If these are the only wires, however, there will be no reliable way to detect which switch is open.  All you will be able to detect is whether both switches are closed or not.

With a ground wire







simulate this circuit

If you also have a safety ground wire, there is another option because the ground and neutral wires should be at the same potential.  In the case that SW1 is open, neither D1 nor D3 will be lit.  If SW2 is open, only D3 will be lit.  If both SW1 and SW2 are closed, both D1 and D3 will be lit.