Electrical – Should neutral and hot wire be tied together if not in use

EDITED FOR CLARIFICATION:

If this is wired as you have drawn it, then it will not be a safety issue. The additional neutral will only share the current in both circuits. Because both circuits are fused for 15A, each neutral will only see a maximum of 15A. This is providing that both neutrals are solidly connected! If one were to become loose or disconnected then the other can potential see the full load, 15A*2=30A.

If anything else is fed from either of those breakers, it becomes a whole other issue! I recommend you wire it the right way. However to answer your question, I don't see it as a safety issue if that is the only circuit on those breakers.

With either breaker off, that circuit will be isolated from the energized circuit. The only common path between the two is the shared neutral. If the energized circuit were to draw the breaker maximum of 15A, the de-energized neutral potential would be at maximum only a few hundred millivolts, not posing a safety risk.

Also it is not against code to have more than one feed in a jbox or switch box.

Here's how you can get a shock from a "neutral" wire: you had multiple white wires, only one was the neutral leading back to your circuit breaker/fuse panel. The rest are extending the neutral to other fixtures/outlets. Let's say that one is a light fixture and its switch is on. When you undid the white wire bundle, the white wire going to that light now becomes hot: voltage is coming through the closed switch and the light. You'd get a shock from that white wire, but only when you'd disconnected it from the true neutral.

Now, as for the volt meter, did you meter the individual white wires to ground, or only the complete bundle? As I noted above, you would only see voltage on that white wire when it was disconnected from the real neutral wire.