One of the most dangerous, even deadly, myths about wiring is the assumption that neutral (white) wires have no current running through them. Even disconnecting them offers no guarantees. If the circuit is turned off at the panel, there is still a strong possibility of a “shared neutral” situation meaning the current will still be flowing.
Nothing can ever be safely assumed when it comes to electricity. Professional electricians operate with standards recognized by other professional electricians, but there's no way to know that every set of hands that have ever touched your electrical system were operating by these standards.
The fact is, if you've ever seen these examples of repairs, there's no telling what kind of improvisation your electrical system may have been subjected to.
If you are attempting your own wiring, be sure to check for voltage between the white wire and a known ground before disconnecting it. When in doubt, turn off the main breaker at the service panel or call a professional electrician.
To illustrate the importance of this issue, let me just point out that a service call is much cheaper than a funeral. Yes, it's that serious!
