What is the "fuse" lead on a xformer primary?

[lgreen]

I've got a transformer with 5 primary wires. The 5th wire is labeled "fuse". What does that mean and how would you use it?

[Enzo]

I can't say for sure this is what YOU have, but many transformers have a thermal fuse inside, tucked between winding layers. If the transformer gets over the fuse's rated temperature, the fuse opens, removing power from the transformer primary.

In many transformers, the fuse is hard wired in series, and that is that. But on some, and if I can find a sample schematic I will post it, the primary wires are brought out separate, and the thermal; fuse is wired to one end, with the free end of the fuse getting its own wire too. This leaves the fuse available to use or you can bypass the fuse.

Recognizing that the primary windings often have very low DC resistance to start with, generally you can find that the fuse wire will have continuity (through the internal fuse) directly to one of the other wires.