Best way to splice to small electrical wires together?

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rv7charlie

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Glad you had good luck with them. But there are better tools for a/c electrical work.

Unless you have Popeye forearms, you can't apply enough force with typical pliers-type crimpers to ensure a gas-tight joint. All the aviation-rated crimpers use ratcheting action, and have calibrated size openings for each size crimp. The good crimps themselves also have two crimp areas; the primary for the wire itself, and a secondary area that grabs the insulation, helping to provide strain relief. Search for 'PIDG terminals'. Not the only solution, but PIDGs crimped with a ratcheting crimper designed for them will give a very reliable joint that includes strain relief outside the stress riser for the wire. And they're basically goof-proof; the system was designed to allow minimally trained workers to rapidly make reliable connections in a production environment. The production tools are breathtakingly expensive, but B&C, SteinAir, and even AmaBay sell versions that are more than adequate & usually sell for under $40.

Soldering isn't difficult, but it does take a bit more training/practice to be proficient, and it's a slower process than crimping.

I don't want to seem too arrogant, but I'd slightly modify Dave's thoughts on mechanical splicing prior to solder. As long as we're not stringing telegraph wires, the mechanical strength of a soldered joint *shouldn't* be too big a deal. I've never been certified for satellite work, but I do have close to 60 years of amateur & pro soldering experience. In my opinion, the biggest deal for our purposes is for the mechanical connection to keep the two wires stable relative to each other as the joint is soldered, and to ensure proper stability on either side of the joint. I've made many simple lap joints that are soldered, and with heat shrink extended well past the bare area onto the insulation to keep the stress riser at the end of the solder isolated from wire movement, I've never had a failed joint. Best analogy I can think of is something like the wires soldered into a sub-D connector. There's no mechanical feature to the wire-to-pin joints, but the housing & strain relief protect the wires from failure. Another would be all the components that are mounted on a circuit board. As long as they're stable on the board, the only mechanical connection for the vast majority of them is the solder itself, yet the assembly survives. Considering it's purpose, solder is surprisingly strong; most electrical 'stuff' that's soldered will fail in some way before the soldered joint itself fails.

FWIW,
Charlie
 

Rhino

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When we had the 'High Reliability Soldering' course in the Air Force (kinda like graduate level), a good mechanical connection was stressed. While solder does not conduct as well as copper, it isn't all that different. Where the rubber meets the road is stress. Solder is much softer than the wire itself, so it has comparatively little resistance to stress on the joint. Yes, you should be minimizing the possibilities of stress affecting the solder joint, but it makes no sense to expend that effort, and then cut corners when it comes to the ability of the joint to withstand stress. Then again, that course was based on the NASA program. :p
 

ddsrph

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My rules of thumb:
  • Solder where I can assure that both ends of the joint are adequately supported against vibration.
  • Use aircraft grade crimp joints elsewhere; with a high quality crimping tool
  • In either case use shrink tubing over the joint both to reduce vibration fatigue and contamination.
Having said that, it's important to note that I have had specific training on how to solder, I have the right tools, and I have the right solder.

I don't use external flux except in very special circumstances. Instead get a good quality rosin core solder. You really shouldn't use external flux, ever, if you can avoid it. Flux has to be heated beyond certain, specific temperatures in order to deactivate it. If it's not, it remains corrosive, and will eventually attack and destroy the joint.

Regarding vibration, that really goes for any joint (mechanical or solder)... enough vibration will eventually fatigue and fail the wire where the solder (or crimp) ends and the "hard" part of the joint becomes "soft" and flexible.

I was certified to solder on satellite builds by NASA (a very, very long time ago)...

FWIW, and good luck!
Dave
I was a electronic tech in Air Force working within the SCF (satellite control facility) I had a course in soldering to work in field maintenance. I read in those days that several hundred pounds was saved in some large missle systems by refining soldering techniques. On end to end wire connections I twist to get a good mechanical connection then solder and cover with shrink tubing using like you suggest a good rosin core solder. On terminals I use un-insulated and crimp then solder and use about one inch of shrink tubing. I don’t trust a crimped only joint. I completely wired one airplane and one car this way and never had a bad connection.
 

rv7charlie

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Solder is much softer than the wire itself
Inarguable. However, when a wire breaks at a solder joint, where does it break? *In* the joint, or at the edge of the joint? A properly executed solder joint on copper wire will never fail within the joint. If there's enough mechanical stress on the wire while it's in service to risk danger to the joint (or even the edge of the joint), there are much bigger issues in the installation than solder strength that should be dealt with.

There's certainly nothing wrong with making a good mechanical connection prior to soldering; if nothing else, it will help to ensure a quality soldering operation. It's actually harder to make a soldered lap joint than most of the various mechanical joints, especially when using 60/40 solder, because it's difficult to keep the joint stable through the cooling cycle of the solder. But what's going on *around* the joint, in the operational environment, is much more risk to wire integrity than mechanical brute strength of the joint itself. It's easy to test; make up a few lap joint test samples using typical wire gauges found in a/c (22AWG to around 12AWG) and do pull tests. I'll bet you fail the insulation at the pull points before the soldered lap joint fails.

Some 'best practices' stuff has been carried forward even though its origins have been more or less lost to history. For instance, the original 'telegraph splice' wasn't soldered at all.
 

dwalker

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My experience in wiring is based in the motorsports arena and is one that can be a little more violent. We avoided solder joints like the plague. Everything solder hate- extreme temp changes, moisture, vibration, and ham-fisted technicians exist in that world. Often all at the same time, not to mention you know, crashing into things, like walls.
Almost exclusively used DTM pins and connectors, and for stuff that was really at risk the Autosport connectors were used.
For a splice of two or more wires an uninsulated metal crimp, ratcheting crimper, and heatshrink with glue inside was typically used. Only certain crimp connectors were used, because cheap ones would fall apart when crimped with the ratchet crimpers, and we typically got them from Wicks or ACS or motorsports suppliers. Heat shrink was almost always Raychem, glue lined for splices and standard for harness runs.
Not the only way to do it, but it worked for us and we had very few wiring issues.
 

Rhino

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Inarguable. However, when a wire breaks at a solder joint, where does it break? *In* the joint, or at the edge of the joint? A properly executed solder joint on copper wire will never fail within the joint. If there's enough mechanical stress on the wire while it's in service to risk danger to the joint (or even the edge of the joint), there are much bigger issues in the installation than solder strength that should be dealt with....
Right. Like mechanical connections. But you make a good point with the "properly executed" comment. Despite our best efforts, we sometimes produce less than stellar solder joints, and it isn't always obvious. A good mechanical connection is cheap (free) insurance against such possibilities. It very often makes the difference between a poor connection and no connection at all if the solder joint fails. Same with crimps. We could argue the physics all day long of course, but I have to ask rhetorically, why not do it when you have the option available, and when it gives a higher degree of safety? Not a reflection on you, but it troubles me when some people cut corners on safety, especially when it costs them nothing. Even if they do it in a non-critical area, it always makes me wonder what they did elsewhere.
 

rv7charlie

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If you'd quoted the rest of that post, I think it would be obvious that I'm not against using a strong mechanical connection before soldering. The reason I brought it up is that the core reason for doing it isn't for mechanical strength of the joint (this isn't wire rope), and believing that can lead a person down the wrong path in subsequent decision making. Understanding the 'why' of a process can also (sometimes) open up additional possibilities for using the process. A good example are the solder splices mentioned earlier. While there are some solder splices that are designed as ground tails, others are just what their name implies; splices. The upside is that they can make a very compact splice (very useful if you're splicing a number of wires in the same area), very quickly. A quality insulated crimp makes a pretty big bump in a wire run, when the wire is small, like signal cable. I actually have a similar splice kit in my shamefully extensive collection of building stuff; if I get bored enough one day, maybe I'll do a video of testing the 'lap joint with a solder-splice' multiple-heresy for y'all. ;-)

edit: BTW, why does the ground tail solder splice get an exemption from the mechanical strength rule?
 

Rhino

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If you'd quoted the rest of that post, I think it would be obvious that I'm not against using a strong mechanical connection before soldering...
I'm sorry. I wasn't trying to say that you were against it. It just sounded like you were minimizing the importance.

edit: BTW, why does the ground tail solder splice get an exemption from the mechanical strength rule?
Beats me.
 

rv7charlie

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It just sounded like you were minimizing the importance.
Well...I might have been doing that. ;-) Seriously, what I was trying to do is to emphasize that the important thing for our purposes is to keep the joint stable (no relative movement between/among the stuff getting soldered) during the act of soldering. A solid mechanical connection is a straightforward method of stabilizing the joint, but it's not the only method.

Once the joint is cool, and properly insulated, and some method is provided to keep any bending movement away from the edges of the solder (the stress risers), the *strength* of the joint doesn't (or at least shouldn't) be any factor whatsoever in the safe serviceability of the joint. Any concerns of joint strength implies that we have heavy components dangling from their wires, or we're using wiring as a pull cord, or we need to rethink wire routing paths.

If you think about it, the vast majority of wire failures are where the wire terminates at a component, whether its soldered, or captured under a screw terminal, etc. And it fails because the wire has been moving relative to the stress riser in the termination (there's always a stress riser).

Again, my goal has been to focus on the 'why'.
 

Rhino

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...If you think about it, the vast majority of wire failures are where the wire terminates at a component, whether its soldered, or captured under a screw terminal, etc. And it fails because the wire has been moving relative to the stress riser in the termination (there's always a stress riser).
And that's often due to poor soldering and/or crimping techniques, which we've both been stressing.
 

Marc Zeitlin

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And that's often due to poor soldering and/or crimping techniques, which we've both been stressing.
Actually, in the approximately 120 different E-AB aircraft that I've inspected, examined, or worked on, there have been a couple of wiring failures due to crappy soldering, a few more due to crappy crimping, but the vast majority of wiring failures, which 99.9% of the time happen at the wire termination, are due to crappy or non-existent strain relief. Strain relieved connections don't fail, even with mediocre crimping or soldering.

IME.
 

Rhino

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Cool. Good to know. Thanks. But I wasn't advocating no strain relief. I was advocating additional care in all those regards.

EDIT: I should also add most of the failures I've observed were on Air Force aircraft, and they had required strain relief (most of the time). Most connection failures we saw were due to bad soldering or crimping.
 
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rv7charlie

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Marc's experience is what I was trying to describe. It's worth noting that in military/NASA stuff, wire routing and support likely got almost as much attention during the design phase as anything else in the vehicle. The wiring bundles are typically pretty 'fat' (internally self-stabilizing), and are well supported at close intervals, all the way to within a few inches of the terminations, meaning there's little to no chance of wire movement relative to the connector (which has internal strain relief), and certainly no movement relative to the termination itself. The maintenance guys largely follow what's already in place, when they do maintenance. In homebuilts, on the other hand, there's virtually no guidance on how critical it is to keep wires well supported as they leave their terminations. We're much more likely to have smaller bundles; often just one or two wires, so there's more risk of wire movement relative to individual terminations. The termination, or rather, just outside the termination, is where the wire fails, because all the repetitive flexing happens where the wire meets that 'hard point'. Same effect as a sharp edged notch in aluminum; all force gets concentrated there, and repetitive movement causes fatigue failure.
 

cvairwerks

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Our stuff at work, has to have support within 6" of a termination (connector, ground block ect...) and be tied every 6" or less, as necessary. Tie tension is determined by what the bundle is....fiber gets minimal tension, while some heavy electrical bundles are tied so tight, that the string tie gives a very audible pop when cut. Ties cannot be around hydraulic, pneumatic, fuel or coolant lines. Certain areas that have the potential for picking up damage due to chafing, are wrapped with teflon tape or sheet. It takes a new kid about 6 weeks to get where they can do string tie well enough that we don't have to watch over them too much.
 

TFF

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I believe all these top tier methods get the job done to the highest standard.

Always in the back of my mind is my Spitfire, which I have owned since 1985, Triumph not Supermarine. It did not come with an overdrive transmission, but I found one and installed it. Wiring was simple. I jammed some Radio Shack 10gauge under a fuse. One that worked. Fed it behind the panel to run along side the transmission tunnel. There is an inline fuse, probably liberated from a car stereo, where the 10 g, red for the people who need to know, wire was stripped and wadded into a ball for the fuse to engage. The other side, factory. That wire runs right along your right leg, in between the seat and the tunnel to a toggle switch. The important connections are the switch, a correct STSP which is now just about impossible to find, and the transmission solenoid. Carefully, the wire, described above, was wrapped around the switch terminal going in. Going out, the switch, not attached to anything just laying there, still has a wire soldered on. That wire was braided to the transmission solenoid wire, to the factory connection. It’s still like that in the shed.

All the wonderful correct ways have no context except you were told to do it right from the beginning and you followed the rules. Coming from the other end of the solution making predicament will demonstrate how exploring and experimenting will show you the limits of each end of the problem. Or it’s what a teenager can get away with on the first car he bought. First car owned, totally different lesson. It’s in the shed too.
 

Rhino

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Marc's experience is what I was trying to describe. It's worth noting that in military/NASA stuff, wire routing and support likely got almost as much attention during the design phase as anything else in the vehicle. The wiring bundles are typically pretty 'fat' (internally self-stabilizing), and are well supported at close intervals, all the way to within a few inches of the terminations....
What you and cvairwerks describe is pretty much what we had in the Air Force, which might explain why I saw more solder and crimp failures. I should also note that most of those failures were perpetrated by folks who had not been to the advanced soldering training.
 

Benpalmer87

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Hello.
I have 4 wires which need to all go to the same terminal on the switch.
What are my options.
I don't think 4 terminal lugs will fit in the one screw terminal.
Terminating the 4 wires into the one terminal, though I don't think this is an acceptable method.
Splicing the 4 into 1 wire, not sure if this is the best idea either.
Terminating the 4 wires to its own buss bar then run a single wire to the switch.
What are your thoughts?
 

rv7charlie

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All wires carry equal loads, or at least similar loads?
I'd do some variation on 'Splicing the 4 into 1 wire'.

You don't mention what kind of terminals, but I'll assume that you're using PIDG crimp terminals.
Option 1 is the '4 into 1', but that can be problematic matching the bulk of 4 conductors on one side of a butt splice to one conductor on the other. I'd certainly up-size the one wire going to the switch lug.

Option 2 would have more connections, but might be easier to do: the old 'tri-Y' like old school engine headers. One pair into a single conductor via butt splice, the other pair into another single via a butt splice, and then the two singles into the terminal that goes on the switch. You can stagger the length of the singles *slightly* to reduce any big knot in the wire bundle from the butt splices.

In any case, build a table showing current handling capability of each wire, and do the math so that the single(s) are sized to carry the same current as the sum of the wires leaving it.

(And make sure the supply wire to the switch is sized to handle the sum of all the capacities of the wires leaving. (Not the actual loads, but the load capability of the wires themselves.)
 
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