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Which Wire-Splicing Method Is the Strongest?

Posted November 24, 2021 5:00 AM by dstrohl
Pathfinder Tags: replicas and kits

Splicing wires doesn't seem like it should be rocket science. Touch one bare wire to another, make 'em stay together, and you're off joyriding in your uncle's hot rod at 3:00 a.m. But as it turns out, splicing wires can be rocket science, with even NASA formulating standards for how to securely and safely make these connections. Nevertheless, gearheads continue to employ a variety of different wire-splicing methods, insisting theirs is the strongest or the most conductive or the most resilient. So let's semi-scientifically determine which is the best.

For this test, I'm considering just straight splices—wire to wire—and not any sort of tap, crimp, or plug-in connectors. (Splice versus crimp is a discussion for another day.) I'm also looking at low-voltage automotive wiring, not household or small appliance wiring, and focusing on the splice, not any covering like heat-shrink tubing or electrical tape. While many kinds of splices exist, I've narrowed down the test methods to four, all of which are commonly used in auto repairs. I'll evaluate each on the tensile strength of its mechanical and soldered connections, and I'll make a note of other attributes, including aesthetics and how the splice affects the wiring itself, all of which is 20- to 22-gauge and comes from my Nissan Leaf's harness.

Discover the merits and drawbacks of rattail, J-hook, lineman's and palm frond splices.

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#1

Re: Which Wire-Splicing Method Is the Strongest?

11/25/2021 12:16 AM

In the 1960's, I was in Electric Shop. We were taught the Edison Splice (Lineman's) which was extremely strong. the only contraindication was that it made the splice extremely brittle.

We were splicing 12 AWG wire.

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#2
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Re: Which Wire-Splicing Method Is the Strongest?

11/25/2021 12:17 PM

When utilizing the lineman's splice on multistrand wire we were taught to first separate the strands, then mesh the strands end to end, then wrap a couple of the strands as indicated, then wrap a couple more strands, and so on. The result was a very strong joint, tapered from thickest in the centre to thin where the insulation starts. The tapering also resulted in a neat joint when taped.

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#3
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Re: Which Wire-Splicing Method Is the Strongest?

11/25/2021 3:00 PM

PS: I think we called it the Western Union splice.

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#4
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Re: Which Wire-Splicing Method Is the Strongest?

11/25/2021 9:21 PM

You're probably right. It's been 60 years since I was in this class.

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#5

Re: Which Wire-Splicing Method Is the Strongest?

11/26/2021 12:20 PM

For a little perspective, physical strength of the joint shouldn't make one whit of difference unless you're joining a load carrying cable (meaning wire rope). The only exceptions would be in situations like the telegraph line example, where the splice provided the electrical integrity (no solder), and also the physical join of two wires, mid-span.

We don't often tow our cars with the electrical wiring, or expect it to support dropped milk jugs full of water. For any properly executed physical architecture, electrical wiring will never see tension loads that challenge the joint. Electrical integrity is a different question. Either a properly executed (with the proper tools & crimps) crimped joint or a properly executed soldered joint will support more physical stress than the wire and its insulation can be reasonably expected to endure. If soldering, the primary goal of any type of physical attachment is to prevent movement while the joint is being heated, wet with solder, and allowed to cool. A simple 'lap' joint that's properly soldered will support more stress than the insulation on the wire is likely to endure.

All joints have 'stress risers', whether crimped or soldered, and need support outside the joint on both sides to prevent fatigue failure at the joint. Quality crimps have *some* built-in strain relief outside the crimp, but the same protection can be added to soldered joints using heat shrink insulation.

FWIW, from about 55 years of building/maintaining electronics.

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#6
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Re: Which Wire-Splicing Method Is the Strongest?

11/26/2021 12:48 PM

Sure, but strength and electrical integrity are not necessarily mutually exclusive. The joint I describe has both, with the added plus that it looks good.

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Re: Which Wire-Splicing Method Is the Strongest?

11/28/2021 8:40 PM

For a secure connection I use solder together up to about #14 stranded, and then go to a split-bolt design....

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Re: Which Wire-Splicing Method Is the Strongest?

11/29/2021 9:55 AM

Don't have a current Canadian Electrical Code, but to my knowledge split bolts are no longer permitted at the street to building connection. There, compression fittings are now the only approved method. Split bolts are still allowed downstream from the main service.

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Re: Which Wire-Splicing Method Is the Strongest?

11/29/2021 2:16 PM

Compression fittings? What sort of compression fitting?

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#10
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Re: Which Wire-Splicing Method Is the Strongest?

11/29/2021 2:33 PM

I suspect that he just means the big crimp type fittings made for service entry cable. I also suspect that they don't want split bolts because you can't tighten them enough to remove all the 'air space' around the wire, inside the split bolt. Any movement will cause the wire to gradually migrate out of the pinched area into the open space, and the 'gas tight' connection will be lost. With properly sized crimps and proper tools, all space within the crimped area is filled with the compressed wire, making a gas tight connection with no area left for the wire to migrate into due to movement.

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Re: Which Wire-Splicing Method Is the Strongest?

11/29/2021 2:48 PM

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Re: Which Wire-Splicing Method Is the Strongest?

11/29/2021 4:56 PM

That's right. And the crimp type fittings are pre-loaded with an anti-oxide paste. It forced all electrical contractors to buy the crimp tool and various dies. The manufacturers of the crimp tool knew the contractors had no choice so they charged hundreds of dollars for the kit.

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Re: Which Wire-Splicing Method Is the Strongest?

11/29/2021 5:28 PM

Not sure if shown method is meant for field work. The compression fittings for service entrance cables are not designed for lines under tension. There are different approved types. One type looks like a big fat shotgun shell. Strip the cable ends a specific distance; insert cable end into each end of fitting; crimp with handtool with proper sized die. In another type the cable ends lie side by side, each in its own compression sleeve. Greenlee is one company that makes tools for these field splices.

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#14
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Re: Which Wire-Splicing Method Is the Strongest?

12/04/2021 6:26 AM

Here is a link to a crimp sleeve and wrap cap that has been used in industrial maintenance and construction for many years.The proper crimp tool must be used to ensure reliable results.If done right,they are trouble free.

https://duckduckgo.com/?q=ideal+crimp+sleeve+and+wrap+cap&t=newext&atb=v280-1&ia=web

There are many crimp connectors available for all size wires,but the proper crimp tool must always be used.

Some connections and splices are required to be CAD welded (thermite),according to local and national codes.

A solder joint should be mechanically strong before soldering.Solder should not be relied on for strength.

Solder has a tendency to crystallize over long periods of time,and become unreliable.

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#15
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Re: Which Wire-Splicing Method Is the Strongest?

12/04/2021 9:24 AM

While I'd agree that electrical/electronic solder shouldn't be load bearing, I'd also point out that copper wire shouldn't be load bearing, either. *Stability of the joint* (no relative movement of the wires) during the actual soldering is far more important than physical strength.

I'd be interested to see any engineering studies showing that solder crystallizes over time. I have electronic devices that are over 80 years old with no evidence of crystallized solder in them, and I have raw (unused) solder that was my father's (some of it may well have been *his* father's; close to 100 years old), that has not crystallized.

I've repaired many devices that had what I suppose could be considered 'crystallized' solder joints, but all were caused by improper prep or technique when the joint was originally made; not by any aging process of the solder itself. If the items being soldered have corrosion on their surfaces prior to soldering, of if the joint moves as the solder is cooling, or not all components in the joint are brought up to adequate temperature, etc etc, it can cause what I suppose could be described as a crystallized joint, but that happens as the solder cools; not through aging. The joint may well have an adequate electrical connection at that time, but may fail days or even years later, as corrosion works its way into the joint. A certain now-defunct consumer electronics mfgr had serious issues with their wave soldering operation on their TV circuit boards back in the 1970s; I fixed quite a few of their 'crystallized' solder joints. They were so bad that we wouldn't warrant our work on them; we could find and fix 2 or 3 bad solder joints on the board, give the TV back to the customer, and a week or a month later it would be back in the shop with multiple bad joints on another area of the board. Rinse, repeat.

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#16
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Re: Which Wire-Splicing Method Is the Strongest?

12/04/2021 10:16 AM

Lead free solder has given many problems due to whisker formation of the tin.

It has caused many circuit board failures,and over time can give joints a cloudy appearance resembling movement during the cooling portion.

The whiskers can even propagate under the conformal coating.

Lead/tin,non-eutectic solders are usually the best choice.

I have repaired many circuit boards due to "cold" appearing solder joints,and I usually solder all of the joints when I find one to prevent come-backs.

Automotive circuit boards are especially bad because of the thermal cycling.

Adding lead to the tin solder reduced the effect,but did not totally eliminate it.

I have repaired old vacuum tube TV's and radios where the solder was still fine,but they had been in storage for many years,not exposed to heat cycling.

Tin itself is also vulnerable to cold weather crystallization.

I still have lead/tin solder on the roll that I bought over 50 years ago,and it still looks good.

Napoleon lost the battle on the Russian front because the tin buttons on the soldiers uniforms fell apart.

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#17
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Re: Which Wire-Splicing Method Is the Strongest?

12/04/2021 10:35 AM

Correction,Eutectic,(63/37)not non eutectic(60/40). I tried to edit, but time had expired,even though it had not expired.(This has been a long standing problem)

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#18
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Re: Which Wire-Splicing Method Is the Strongest?

12/04/2021 10:43 AM

Yeah, the lead-free solders are a whole 'nother issue. I should have added that in the earlier post.

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#19
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Re: Which Wire-Splicing Method Is the Strongest?

12/04/2021 10:47 AM

Here is a link that explains the difference between the two types.

https://www.youtube.com/watch?v=ZmCBXvm6C6E

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Re: Which Wire-Splicing Method Is the Strongest?

12/08/2021 8:37 AM

One addition to the lineman's splice which reduces its brittleness: strip a bit more insulation, so that you can add extra turns of copper over the insulation:-

Solder up to and just past the end of the insulation, then, add heat shrink tubing to cover the whole joint (past the loose copper). This adds some strain relief.

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Re: Which Wire-Splicing Method Is the Strongest?

12/08/2021 9:10 AM

If I think the joint is going to encounter a lot of vibration and physical shock,I will coat the joint with hot glue before applying the heat shrink tubing. This will waterproof and absorb vibration while also provide some strain relief. You do not need a hot-melt gun,simply use a cigarette lighter to heat the end of the glue stick, then rotate the molten end around the joint. Wait for it to cool,then apply the heat shrink.It will force some of the hot glue out,and completely seal the joint. I have made many joints like this,and have had no failures after many years. No hot glue? Use a bottle cap in a pinch.Apply the molten plastic to the joint,same as you would hot glue.It has higher melting point,so heat the shrink tubing till you see the plastic flow out the end.

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#22
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Re: Which Wire-Splicing Method Is the Strongest?

12/09/2021 6:47 AM

You can buy glue lined heat shrink tubing, which gives you a waterproof joint, but your method probably gives a better strain relieved joint.

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Re: Which Wire-Splicing Method Is the Strongest?

12/09/2021 8:07 AM

"One should never rely on solder as a sole physical joint.A good mechanical connection should be made before soldering.

Apply heat to the joint,and apply solder to the joint,not to the soldering tip.Allow the

solder to "wick" into the stabilized joint."

This is from a soldering class circa 1960's.

I think the same rules still apply.

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Re: Which Wire-Splicing Method Is the Strongest?

12/09/2021 8:19 AM
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#25
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Re: Which Wire-Splicing Method Is the Strongest?

12/09/2021 8:22 AM

In a pinch,on automotive off road wiring,I have used the hot-melt glue over a good physical connection with no shrink tubing.When I reached a civilized portion of the planet,I taped over it.No problems.

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#26

Re: Which Wire-Splicing Method Is the Strongest?

12/09/2021 8:27 AM

Here is a unique twist on splicing(Pardon the pun)

Twist the wire the same as a cucumber vine curl.

It reverses direction half way up the stalk.

A pulling stress will make one curl tighten if the other one loosens.

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