General questions regarding splicing wires

Thread Starter

electrosn

Joined Jun 9, 2022
2
Hello,

In most of my electronic projects, I have soldered wires together, covering them with heat-shrink afterwards. Recently, I also found out that there are heat-shrink self solder splice connectors (example), as well.

My questions are mostly regarding the reliability of splicing methods, electrically and mechanically. Is higher resistance in the spliced section the only electrical problem created by splicing? Is this worse than introducing a connector along the way? Is it possible to crimp wires together instead of splicing with solder, and is it any better?

Someone might have a good article or manual regarding this, all I found was this video, with instructions for splicing to Nasa standards:
 

crutschow

Joined Mar 14, 2008
30,122
A good solder joint is very strong mechanically and generally has a lower resistance than a connector.
There are crimp connectors to butt join wires (such a below), but I would consider them to be less reliable and have a higher resistance than a solder joint.

1659622250685.png
 

ThePanMan

Joined Mar 13, 2020
433
When I was in commercial aviation manufacturing, stringing wires, we used those solder sleeves everywhere. Far more reliable than butt splices. When in the oilfield manufacturing sector pull strength was tested every week to make sure the operator was performing flawless joints. With butt splices, one assembler was horrible at it. Their splices could be pulled apart with simple finger pressure. They should not pull apart with (the smallest ones) if I remember this correctly, 35 pounds of force for 16 gauge splices, and I was able to extract the wires from the splices with pinky finger force. No way on earth could my pinky's pull that much force.

The assembler complained that I was ripping their work apart. Supervisors gathered. Managers gathered. Engineers gathered. Then I was called into the ruckus to defend myself. I demonstrated how easily the splices were separating. Then I cut the plastic off of one of the pulled apart butt splices and showed how the operator crimped the plastic and barely dented the metal crimp barrel at all. MY manager stood silent with a half smirk on his face knowing full well that I was not only right but also able to defend my rejection of their work. That assembler never asked for me to inspect their work again.

Funny though, when people in the shop got sick, hurt or suffered a death in the family, people would come around taking up a collection for so-and-so. I always contributed generously. But when I ended up in the hospital no one but that operator bothered to even send me a card. The one person I thought was least likely was the only one to express "get well" wishes. After that when someone came around taking up a collection I told them to beat bricks! I've never contributed again to anyone who suffered some kind of malady or loss.

Regarding those solder sleeves, some were soldered using hot air, others were soldered using intense focused light. Since I wanted to make the same sort of splices but didn't have a sufficient heat gun I found a projector lamp with reflector and used that as my heat source. Let me tell you - SUNGLASSES were barely able to minimize the brightness of the focused beam to where I could actually watch the solder melt and adhere to the wires.

Other solder methods I've used was to lay the two wires side by side, one from the left, one from the right, and take a small piece of wire, usually from a scrap piece of wire and wrap it around the two wires. Then solder them. Then slip the shrink sleeving over them. The two problems I had with that was 1) holding the wires in place while wrapping them, and 2) forgetting to put the sleeving on before making the joint. THAT sucked!
 

SamR

Joined Mar 19, 2019
4,302
Western Union type splices were intended for aerial wires that were run pole to pole and subject to ice loading. Not something needed otherwise unless there is strain loading of the wire. A simple wire twist is usually sufficient.
1659631009320.png
Or for stranded wire with very small strands.
1659631235251.png
Then bend the splice parallel to the wire after soldering or can be taped or trimmed and wire nutted. Taping after wire nutting is also done for wet locations.

I can't find an image of a ring splice! Not used as much these days because of PCBs instead of point-to-point wiring using terminal strips. Simply strip the insulation, insert the wire through the terminal ring and twist the end back around the stripped wire a few times. Trim the end off and then solder the entire connection, both ring and wire. I also sometimes use heat shrink especially for multiwire cable connectors subject to strain to offer some strain relief.

In all cases, I prefer a heat shrink wrap after splicing but don't forget to put the heat shrink tubing over the wire before splicing it! ;) Also, for wet locations use the heat shrink tubing with adhesive inside it.

As Ian said, anything larger than ~AWG 8, you will probably want to crimp it. Absolutely will for /0 and MCM AWG sizes

Another good use for heat shrink is over wire cable when cord grips are used to make them fit snugly. Sometimes more than 1 layer.
 
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MisterBill2

Joined Jan 23, 2018
12,431
Often with wire splices the big challenge is mechanical durability. The soldered portion of a joint does not flex , and so the sections of stranded wire at the ends of the solder joint tend to get all the flexing concentrated in one spot, and that is where mechanical fatigue tends to result in broken strands, and eventually a break. Many spliced joints are not soldered, just twisted and taped, and those do fail. The well done ones fail open circuited, the poorly done ones may fail with a short circuit and a flash of spark. And some poor splices overheat when carrying much power, resulting in a bit of fire.

My last important splices were in CAT-5 data cables, where two cables were about 25 feet too short, and the very long runs went through flexconduit in a wall and could not be pulled out to put in longer cables.
The general consensus is that CAT 5 cables can not be spliced so that they will still provide adequate performance. But it can be done, it turns out. The trick is to not disrupt the twisting or the proximity within each pair of conductors The conductor splices are at points at least half an inch apart along the wires, which, after having had a half inch of insulation removed from each conductor are re-twisted to the same number of twists per inch, and then the bared sections are tightly twisted to each other at right angles to the pair. Then the twisted splices are very quickly soldered, to avoid heat damage to the insulation and trimmed to about 1/4 inch, and folded back in opposite directions. So the twisted pair has its twisting not changed and the spacing between the pair is unchanged. For each pair splice the insulation is just one bit of masking tape folded over the two exposed twisted soldered connections. The proof of the concept was that it works very well at the speeds that the folks setting up the installation originally intended.
The point being that spicing can be done without adding big SWR bumps in a data line.
 

ThePanMan

Joined Mar 13, 2020
433
Whenever you come across a really big cable (25mm^2 and above) where a low resistance connection really matters, it will always be crimped.
Been quite a long time since I used a hydraulic crimper for 00 & 000 gauge. In my hobby I don't have much need for tripple ot gauge wire. Biggest wire I mess with is 12 gauge stranded. More frequently it's 16 gauge, or 18. Rarely do I go smaller than that as far as crimping goes. 20 gauge is most typically solid wire, not stranded wire.
 

ThePanMan

Joined Mar 13, 2020
433
Um, there's always ultrasonic welding. Seen that before.

Off topic - this bugs the heck out of me; there's an internet provider that claims "Super Sonic WiFi". REALLY? Faster than sound? Must be some damned loud internet modems out there.

Just lap solder your wires together and slide shirnk sleeving over it. OR order some solder sleeves. Those solder sleeves have a glue in them that lends extra strength to the joint and seals them from moisture.

Here's one example:
 
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