The notes for soldering worksheet answer to Question 2 about tinning suggest that stranded wires should be tinned prior to clamping in a terminal strip.

Although in the short-term this appears to be a good idea, in fact it is quite a bad idea because solder cold-flows under pressure - i.e. in a terminal strip - so the wire will become loose in time, with obvious consequences !
I'm sure this practice is banned under certain standards but I can't remember where I've read it right now. I'll report back if I find the reference.

"Notes:
Some wire may be purchase "pre-tinned" to save you this step, but most electrical wire is not. Here is a helpful hint: tinning the ends of a piece of stranded copper wire really helps to prevent individual strands from bending and breaking away when the wire end is clamped in a terminal strip! "

 

As I said before - it's a bad idea due to cold flow of the solder.
This is clearly stated in BSEN 60950-1:2006 Information Technology equipment - Safety, Para. 3.3.8.
"3.3.8 Stranded Wire
The end of a stranded conductor shall not be consolidated by soft-soldering at places where the conductor is subject to contact pressure unless the method of clamping is designed so as to reduce the likelhood of a bad contact due to cold flow of the solder.
Spring terminals that compensate for the cold flow are deemed to satisfy this requirement.
Preventing the clamping screws from rotating is not considered to be adequate."

 

Hmph... That dang BSEN 60950-1:2006 will get 'cha every time. Im playing 3.3.8 in tonights pick 3 lotto.

Now back to reality. I have always been told that stranded leads stay bare in high voltage applications. I had no idea that it was required the IT level. It makes sense. If the solder cold flows, you reduce contact points and can cause unstable data connections. Especially in areas prone to vibration or severe temperature changes.