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Thread: NASA technical standard document: Crimping, Interconnecting Cables, Harnesses, Wiring

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    Jon
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    NASA technical standard document: Crimping, Interconnecting Cables, Harnesses, Wiring


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    This may the a NASA approved method laying 2 cables side by side lashing then soldering but you will never see me doing a connection or splice in that manor.
    I've always been of the school to have a good electrical connection you must first have a good mechanical connection. simply laying the conductors side by side only offers a minimal amount of conductor contact area lashing with same type conductor material helps but still just barely offers more actual conductor contact Solder is for holding the cables together not the primary conductor. for side by side a far better connection would be to twist the conductors together for at least 4 diameters of the conductors this insures a solid mechanical connection even without solder but is not to be considered the final step in making a good splice solder needs to be applied to permanently bind the conductors.
    For the end to end running splice on stranded conductors the strands should be exasperated or splayed open then put together as one would do the fingers of their hands Then the strands should be twisted in opposite directions and soldered
    over the years I have found countless wiring harness problems in the automotive field where the splices were done exactly like NASA's shown method It only takes a momentary overload to heat a cable to the point of melting the solder which then becomes a hidden fuse in a loom or harness the conductor need not even become hot enough to damage the insulation before it fails
    For crimp connectors I rarely use the insulated type or if I do I remove it before crimping then solder the connection after crimping re insulate and it is good to go
    That's my opinion and it has worked for me since my very first vehicle
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    As an army helicopter repairman in 1956-1958, I was taught that a splice or termination is never soldered because the stresses of the extreme vibration in a helicopter would concentrate at the transition zone between the rigid, soldered wire and the unsoldered wire leading to the possibility of an eventual wire break at that point. As a now retired 40-year noise and vibration engineer, that analysis still makes sense to me. You want the bending due to vibration or repeated handling to be distributed over as long a section of wire as feasible to minimize fatigue at the focal point of bending.

    Looking at the figures in the NASA document, I can see that the soldered splice of figures 19-8 and -9 could provide good fatigue resistance PROVIDED the parallel wires were bound together with tape or shrink tubing (not shown, and shrink tubing didn't exist in 1958), so that the stress of vibration or repeated bending would be distributed over a length of unsoldered wire, but the splice shown in figures 19-10 and -11 would concentrate stress at the soldered transition zone despite the minimal support offered by the shrink tubing.

    And, except for a temporary emergency repair, why would you ever allow a splice in the middle of a wire run at all?

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    Frank S's Avatar
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    awright there is a huge difference in automotive and aircraft electrical systems That being said back in the days of the F111 project my uncle was put in charge of finding a phantom fault in some of the circuitry turned out to be just as you described. However it is almost impossible to rib apart a harness from any make model or brand of automobile and not find several mid stream branch terminations where smaller wires are soldered to larger feeder cables not so much any more as most are now electronically fused as in spot welding the process is far superior to simply laying a wire next to another then wrapping it with a tie wire and soldering the connection. Many still solder short lengths off smaller conductors inline of the larger cable to make a fuse-able link or thin out several of the strands in mid stream of a conductor making that the fuse point then they cleverly hide them in the harness. If you cut open a harness and find a length of shrink tubing on a wire with no apparent reason for being there carefully remove the insulation and you will discover as much as 50% of the strands are severed or the cable will transition from heavy strands to much finer strands in that section how they do that I don't know
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    One of the major problems the layman faces when using crimp terminals is over crimping or under crimping
    over crimping distress the conductor which can cause it to break under crimping has more obvious faults as the wire can pull out
    When I simply cannot solder a crimped connection I always use a high quality terminal never those that come in a kit found on the bargain shelf. I also use Klein dimple crimp pliers and for larger cables I have a 16 ton hydraulic crimp set with properly sized dies for each gauge or or diameter of the cable
    for making an inline splice I use the barrel butt connectors that allow the 2 ends of the wire to pass completely through this yields a cable to cable contact and can never come apart due to 1 crimp being loose
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    Yes, Frank, I am aware of the difference in criticality AND vibration environment between aircraft and autos. However, what surprised me was that what Jon showed was a NASA document - applicable not only to aircraft, but presumably to space vehicles!

    I agree with your discussion of proper crimping but the vast majority of home machinists and hobbyists will be using non-professional tools and very few will have access to 16 ton crimpers. Many will be using pliers or a hammer, rather than even hardware store crimpers. To guaranty a proper crimp one really should use the tool specifically designed by the manufacturer for his terminals. However, even knowing this, I use whichever of my collection of perhaps two dozen professional grade manual crimpers seems to match whichever of my collection of perhaps thousands of terminals matches my project and I always give a good tug to my terminals after crimping. Luckily, none of my projects fly.

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    Interesting discussion.
    If we are talking vibration try old British motorcycles, enough to make your fingers and backside go numb and a good test of wiring connections, out in all weathers too.
    I have given up on Lucas bullets and now use crimped spades, I have BICC manual crimp pliers that press a dimple into the wire and seem to work well providing any wires are secured to something and not allowed to move and stress the joint. I use the insulated type and always crimp the insulation onto the wire sheath afterwards, not had any problems so far.

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    olderdan; in my younger days motorcycles were an obsession of mine 3 or my favorite Britt bikes I owned were the Triumph trident the BSA 500 single and of course my Norton 850 commando in 1980 a friend bought Kawasaki KZ 1100 and started talking trash so naturally I had to accommodate him the old Norton never made me run more than 2 in a 2 out of 3
    I suspect that the BICC crimp pliers are similar to the Klein which are designed with 3 dimple sizes and an insulation crimp cavity
    A friend of mine gave me some terminals that I like they are made with low temp solder in side and heat shrinkable insulation the insulation is much longer and the solder flows as the insulation shrinks still need to pre-tin the conductors IMO for best results
    awright; the purchase of the hydraulic crimp set was out of pure laziness any hobbyist or home machinist should have the ability to make proper crimps if they just take a little time to make the right tools for the job as in my 500 MCM cable end swage block That I made when I was setting up my off grid solar system


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