I don't know of an application where 'tinning' of the stranded wires is not acceptable, or even preferable.
The balling up of the stranded wires as you describe is never acceptable.

Are the push-ins actually listed for smaller sizes of stranded wire?

Thanks for your replys. Yes, the push-ins are rated for stranded wire. Let me list on here all the types of wires that are compatible with it: #18-#12 AWG Solid, #18-#14 AWG Stranded, #18-#12 AWG Tin Bonded Stranded. I assume that Tin Bonded stranded is not the same as a solder-tinned wire because this device can only handle regular stranded gauge wire up to 14 AWG with 12 AWG being too big, especially with solder melted over it. Here's another question, is it o.k. to apply a small amount of solder to the tip of spinned stranded wire that comes on AFCI breakers?

I have some doubts about overall tinning of stranded conductors. Solder is meant to seal and reinforce a connection that's already mechanically solid. It's not as good a conductor as copper.

However, I don't see anything wrong with tinning just the last 1/8" or so of a stripped end to help keep the strands together. In fact I've seen that done on zip cord used in factory-made table lamps.

When connecting stranded wwire to a screw terminal, try twisting the strands counterclockwise instead of clockwise. It helps keep them together while you tighten the screw.

" Yes, the push-ins are rated for stranded wire. "

I see a lot of restrictions on stranded wire.

The number of wires making up the strand, the size of the strands, etc.

I saw at least one that allowed only 7 strand #18.

I have a pieces of 4/0 in my office that has thousands of strands (they are around #38).
It is as limp as a noodle.

It is designed for places that require movement of the wire over a joint.

The only connections it can be used with are fully enclosed screw lugs with a pressure pad bearing on the wire.

At least the visibility in many of the push in connectors allows you to see if strands cam out of the bundle.

My under cabinet lighting is stranded and didn't want to work with the connectors so I tinned the wires. It worked great after that but the current draw is very low.

"My under cabinet lighting is stranded and didn't want to work with the connectors so I tinned the wires. It worked great after that but the current draw is very low."

I hope that is line voltage (120 V) lighting and not low voltage.

Whilst it would appear at times tinning is acceptable (some wires in appliances come pre-tinned at the ends) I don't think it's wise. I have found the connections tend to gain resistance which generates heat, which generates resistance.

Use the twist marettes or an approved crimping connector.

Yes Brick 120v puck lights. I do not think there is enough current to cause a problem in this instance.

"I have found the connections tend to gain resistance which generates heat, which generates resistance. "

Only if you make a bad solder joint.

Rookie registered today to answer questions asked almost 3 years ago.
That aside, the advice given above is OK.

The op is talking about push in wire connectors (wagos) not back stab receptacles. There is a big difference in the application.

It appears this original post was about the push-in connectors that can be used instead of wire nuts.

This reply - 3 years late - is somebody talking about problems using backstab receptacles & switches - which we already know all about.

Obviously, they did not read, or understand, the original poster's message.

Wow, btharmy, 6 minutes apart - but same conclusion. I think you can probably type faster than me!