There is generally not a neutral wire in a switch box. There are two ways the box in a switch can be wired. It depends on whether the live current plus neutral wire plus ground - the standard three wire Romex - first goes to the light fixture, or whatever the load is, or to the switchbox. Both are employed and both are legal. When it goes to the fixture, a two wire line goes to the switchbox. Often it is a Romex with ground that is used for that, in such cases the ground wire is not really needed for anything. The black and white wires in such a case may as well be both black, as neither will ever be a neutral wire. The way we electrician types think of it is: you hook the white wire going to the switch to the hot wire, the black wire in the light fixture, and in the switchbox you hook the white and black to the two terminals on the switch. This is assuming it's a regular old switch with no need for any current doing anything internally. More on that later.

When the switch is turned on, we call it turning white into black, and the black wire is then taking live current back to the fixture box where is connected to the black load line on the fixture. The white neutral line coming into the light fixture box is hooked to the white load line on the fixture, it never goes anywhere near the switchbox. When all is said and done, it's as if you have a switch right at the light fixture box and it interrupts the black, live line just before he reaches the fixture.

In the other method, the live three wire Romex goes to the switchbox and a two wire line plus ground - a standard Romex bundle - is sent to the fixture. The white neutrals are wired together. The black going to the fixture is on one side of the switch, the live black coming to the switchbox is on the other side of the switch. The green or bares are wired together and you ground the light fixture with it.

The applications where this can become difficult is where you have a switch, such as some timers, that require a little bit of current to make the switch work. Your situation is maybe working because the ground going away from the switchbox was hooked to the ground at the fixture, something that is really not necessary and is often not done. Certainly not in the old-style wiring, more and more it is done in the new. A lot of the safety on this would depend on whether or not the ground wire coming into the switchbox originally was the green insulated type or the bare type. Doesn't really affect fire hazard much, it might mean one would get a mild shock handling the light fixture at some point. Current going through bare wire is not usually a fire hazard by itself. If the line gets so hot that it will start a fire, it will be happy to use the plastic insulation as kindling for the fire.

It can sometimes be a real headache getting a neutral line into a switch box like this when you need it. I have gone to great lengths to do so at times.

I tend to get cavalier about the need for a groundline as so often I'm wiring into existing older wiring in old houses that don't have a groundline. Putting one in place can be very labor-intensive and it's often not needed. A groundline is a good idea with hand power tools because if any short develops where current would be going into the handpiece, it is instead ran off through the ground line rather than through your body. My guess is a groundline in a light fixture actually accomplishes anything in one out of a million applications. But I don't think the law sees it that way.

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1986 300SDL, 362K
1984 300D, 138K