It's not a good practice. The tinning wicks out a bit on the strands making the wire stiff. And any movement of the wire can cause the wire to break near the connector. I believe the auto industry, etc. have completely gone to crimp only. And as well as many other industries to no tinning or soldering of the connection. Spin the strands in your fingers before you poke the wire into the connector, then crimp. Works well if the connector is sized well for the wire size.

On the insulated connectors, there are some premium connectors that can be crimped thru the insulation successfully but they are expensive. Most of what you find in the auto stores are pretty sad material which crushes under crimping (almost like hard licorice) and are just as well left bare. Then heat shrink them if necessary.

I *believe* the answer is no to soldering before crimping. The crimp was optimized to deal with strands that can 'float' around in the crimp before reaching their final position. Also I have seen issues with soldering the tips of wires before inserting them into DIN rail terminal blocks; the wires  get loose over time as the solder gives.

If you are hell bent on soldering, you could solder after crimping, if you are using non-insulated terminals. The only issue I have seen (so far!) with soldering after crimping are certain pin-and-socket connectors; the solder wicks up wire and the strands bend at a location that wasn't designed for, and then the wire breaks there, under vibration. OK maybe two issues, trying to solder gigantic 4/0 cables with lead free solder, even with a solder pot, I could never get it to work.

If this is the route you are going to go and you have your soldering iron out. I would crimp first to secure the wire. Then solder it. The crimp connector needs to collapse into the wire. If you solder first. The wire can't spread out as it's solid.

A good crimp is what I am trying to insure.  I have a Klein Tools 1005 crimping tool which will do both insulated and non.  In the past I almost had to stand on the crimper (not the Klein) to get a tight crimp on the wire.  At that time I was using insulated so have decided to switch to non insulated hoping for a better crimp.  I have purchased 

uxcell® 200Pcs Metal Non-Insulated Fork Spade Terminals SNB1.25-4 AWG22-16 19A  from amazon.

Orkybrown

I have used the crimp first then solder technique with good results; mostly for marine applications, not so much trains. Just takes more time but makes a bullet proof connection that will resist corrosion. If you live in a high humidity area its not a bad idea.

Rod

Sometimes doubling the wire over to fill the opening in the crimp helps, especially with small wire. 20 gauge and smaller.   The correct tool is also important.

Most crimp on connectors have a split side. The indent should be on the solid side.

You can add shrink tube, as mentioned,  for additional insulation.

A set of Weaver E8 trucks re-wired for an electronics/ motor upgrade.

orkybrown posted:

Is it a good idea to tin 20 or 22 awg stranded wire before crimping on to a "red" spade connector.  I believe I will be using non insulated connectors.  I will use shrink wrap.  I seem to remember reading it is not a good thing to do.  It makes it easy to fit in it into the ferrule with out strands splitting out.  Due to the wire size I am planning to fold over the wire before entering it into the ferrule.  Any ideas?

Thanks for any advice.

Orkybrown

You are correct. It is better to leave the stranded wire non-soldered. The result with a crimp connector is a mechanical connection that has flex. Folding over is a good idea with 20/22, so strip it a little longer.

I use the non-insulated terminals.  I put a very small amount of no clean flux on the wire prior to inserting in the terminal.  I twist the stranded wire to help get it into the terminal.   I do the crimp and then I add solder to the interface of the wire and crimp barrel closest to the terminal.  The flux will enable the solder to quickly wet to the interface and usually wicks up into the barrel.  Most terminals are tin plated, so if the wire and terminal are clean and solderable it melts and wicks very quickly.  Then I install the heat shrink tubing over the terminal barrel and shrink it.  If the other end of the wire is already terminated, then you need to remember to add the heat shrink before crimping the wire. 

A comprimise is ok. At just the tip solder it, bare at the crimp, leaving bare wire on the pig tail side especially, it can provide pull through protection. Folding, fill the loop. Terminal solder- just a bit on the connecting side of the tube, again leaving the pig tail unsaturated. Seating insulation fully into the terminals sheath is a good idea for long term life too.

Can you suggest any good sources for the "brand name" connectors.  I surfed around some but didn't find much.  I don't want to have to redo the crimps just because I use inferior ones.  I don't mind paying more for quality.

Then order brass ones. Often there is a mil. Or metal gauge notation in specs. I really like the shrink tube sheaths too. I haven't needed to buy in so long my supplier closed near twenty years ago, lol.