The "normal" install would be that you have live/neutral/ground coming into the box and live/neutral/ground coming out of the box. The neutral in will be connected to the neutral out. The live in will go to the switch and the live out will go from the other pole of the switch. The ground in will go to the ground on thee switch (and sometimes to the box) and to the ground out. If the original live/neutral/ground is actually going to the fixture and not the switch, then you would have a switch loop. You would only have 1 set of wires coming into the switch box. The live would go into the switch. The white wire would be marker black and be connected to the out of the switch. It needs to be marker black to show it is being used as a loop of the live and not as a neutral. The ground would go to the switch and sometime the box itself. It is important to note that if you use a switch loop, the wiring at the fixture will be live even when the switch is off. Either way works fine. Which one you use depends on where the power is actually coming from. If the rest of the circuit is in the wall, it is usually easier to use the first method. If the rest of the circuit is in the ceiling, it is usually easier to use the second method.

It's a GE load center. The switch I plan on using is one made by Interlock Technologies. I can only find one type that GE makes and it is not for my type of panel. The interlock tech switch is pricy by seems to be the only alternative. I could easily make one myself but I suppose the local authorities would frown upon that. Can I run that wire through the sub panel and leave the isulation on it until it enters the main load center?

Much as with your other post TAPE is not some magic thing and does not change an illegal installation into a legal one. Your comments are confusing. If the wiring is ROMEX (a trade name for type NM cable), it must enter the box through a listed fitting (it's not really an insulator, it's a connector that keeps the wire from chafing on the metal and provides some sort of friction to keep the wire from moving. Many of the fittings are made out solely out of metal). There are boxes that actually have the fittings integral to the box (you can tell this because they'll have some sort of clamp that holds the wires in place built into the box. Under no circumstance should the individual conductors of the type NM cables be exposed from the outer cable sheath outside the box.

"I have seen this warning on literature for fixtures that did not have especially heavy internal wiring, and have always wondered what the problem was. " It has nothing to do with the internal fixture wiring. Since only short sections are used, higher temperature rated insulation is not a significant cost. The problem comes about with compact fixtures and enclosed bulbs. You will often notice foil faced insulation on the back of the fixture mounting plate also. Older NM cable used PVC insulation only rated for 60 C. If the fixture generates heat it has to go somewhere, and it will cook the old PVC insulation in short order, causing it to become brittle and crack (sometimes without any movement of the wires). You do not have to rewire an entire house, just make sure that the permanent wiring entering the fixture box is 90 C rated. Newer NM wire uses a different insulation (THWN even though it is not marked that way). Some of the comments on the Bob Villa site are wrong and stupid. Unless you want to have overheated wiring and the possibility of arcs and resulting fires, change the wiring to the fixture box to 90 C or do not use the fixture.