If you are connecting to actual female pins, it does help to have the right sized male pin crimped onto your jumper wires. But if you're just using them on a breadboard, bare wire ends are fine. Just make sure to cut the wire with diagonal cutters, not scissor-type cutters, so that you get a nice pointy end. The shearing action of scissor type cutters can sometimes roll the wire end enough to make it snag in the breadboard.
Quoting from the great Wiki
"Like other wire, magnet wire is classified by diameter (AWG number or SWG) or area (square millimetres), temperature class, and insulation class.
Breakdown voltage depends on the thickness of the covering, which can be of 3 types: Grade 1, Grade 2 and Grade 3. Higher grades have thicker insulation and thus higher breakdown voltages.
The temperature class indicates the temperature of the wire where it has a 20,000 hour service life. At lower temperatures the service life of the wire is longer (about a factor 2 for every 10 °C lower temperature). Common temperature classes are 105° C, 130° C, 155° C, 180° C and 220° C."
Calculation of breakdown voltage (Test acc. To IEC 60851.5.4.2, cylinder)
The breakdown voltage depends mainly on the thickness of the insulation (see formula below), but also on the bare wire diameter, the application temperature of the coil and the type of enamel.
Calculation of average values Ds:
Ds = t x Vμ [Volt], with
Ds : breakdown voltage
T : increase due to insulation,
t = da – dnom, : wire diameters with and without insulation
Vμm = volts per micron insulation (dependent on type of insulation)
Example:
Test with cylindrical electrode (round wire)
dnom 0.071mm (bare wire nominal diameter)
da = 0.083mm (wire with coating)
t = da – dnom = 0.083 – 0.071 = 0.012mm = 12μm (thickness of insulation between wires)
Vμ = 205 V/μm, therefore
Ds = 12μ x 205 V/μ = 2,460 V
Best Answer
NASA, in the NASA Training Program Student Workbook for Hand Soldering, page 9 et seq., say:
I think NASA is a reasonably authoritative source for that.
At a guess, I would say that one of the reasons is to avoid embrittlement of, or other undesirable effects on, the insulation. Also, allow the tinning to flow all the way to the insulation could push flux inside - flux should be cleaned off after the soldering operation and that can't be done if it is stuck inside. My suspicion of wire embrittlement through heating looks like it could be unfounded, as thermal strippers can be used to melt insulation to remove it without damaging the wire.
It is desirable to have no stress or strain on the tinned portion of the wire (because tinned wire is more brittle). That can be achieved by clamping the insulation to ~something~. If it is in an environment where there is high vibration and/or thermal cycling, it may or may not be desirable to leave a curve/loop in the wire, but that would require an analysis of the operating environment.
I refer you again to the aforementioned NASA document where they repeatedly refer to "Proper insulation clearance" after making a soldered connection with tinned wire.
If you want insulation over the tinned portion of the wire, you can use heat-shrink tubing. It is available with an adhesive inner coating which is activated when the heat shrink tubing is heat-shrunk, and with the adhesive can provide a watertight seal.
However, Asmyldof points out that:
[I changed "room" to "length" in the quote.]
So heatshrink tubing is not a substitute for proper support of the wire.