How-To Geek

How to Splice Wires to NASA’s Standards

NASA is particularly precise when it comes to splicing wires; there’s a lot at stake when you’re sending people into space. Learn how to splice NASA style by checking out their guidelines for splicing wires of all shapes and sizes.

Over at MAKE Magazine there was a debate over the the proper way to splice a line for maximum connectivity and strength. The debate was settled when someone trotted out the NASA standards for line splicing and cable connections. You can check out the full Standards Guide at the link below.

NASA-STD 8739.4 – Crimping, Interconnecting Cables, Harnesses, and Wiring [via MAKE]

Jason Fitzpatrick is a warranty-voiding DIYer who spends his days cracking opening cases and wrestling with code so you don't have to. If it can be modded, optimized, repurposed, or torn apart for fun he's interested (and probably already at the workbench taking it apart). You can follow him on if you'd like.

  • Published 03/1/12

Comments (18)

  1. Benjamin Spaulding

    That is the way I was taught to splice wires prior to soldering. That was 20 years ago when I was a car audio installer. Believe it or not, that was Circuit City’s standard process. We weren’t allowed to use crimped connectors.

  2. Dorothy

    LOL! I remember when it was called a Western Union splice. Ain’t new to me, whipper-snappers!

  3. Steve-O-Rama

    The really cool thing about that linked .pdf is that there’s a lot more information in it than merely how to do a lineman’s splice. Among other things, it describes how to properly wrap and bundle wires, as well as how to install crimp connectors (yes, those are in there, despite being ‘evil’ lol). Point is, there are a variety of ways to properly splice two (or more) wires together, but there are a far greater number of ways to do it wrong.

    Next time I see some fool twisting a pair of stranded wires together and then wrapping a bit of cheap vinyl electrical tape around it…WHAM! He’s getting hit upside the head with a hard copy of this guide! :)

  4. Dave

    In critical places I usually solder splices. Then I usually use shrink tubing. I’m sure I’m all for good splices, even good cable management, especially in spacecraft. But a 114-page document (though there are some pages “intentionally left blank”) to tell how to do it? I wonder how many man-years were spent in its development. That’s the government for you!

  5. r

    oooooh….getting sleepy…Zzzzzzzzzzzzzzzz

  6. kenedy123

    Good to know about the How to Splice Wires to NASA’s Standards

  7. myron

    Thanks for giving the more information about the How to Splice Wires to NASA’s Standards

  8. Perry

    The funny thing is you could never splice a wire like in the pictures. Take a good look at the wrap and you will notice that the wire pointing right starts by wrapping clockwise around the other wire but ends up being wrapped counter-clockwise. And the wire pointing left is the same.

    I wonder why they didn’t use pictures of actual finished product!!!

  9. EvenSteven

    I’m with Dorothy. I learned that splice technique somewhere in Kansas as we were stringing the first Transcontinental Wire while working for Western Union.

    The splice is really strong and takes tons of pressure to break.

  10. Philly

    You’re dead right @Perry! They’re contrived, photo-shopped images; and plain wrong! Obviously put together by someone who’s never done it (or who has a sense of humour)!

  11. J. Anthony Carter

    I’m with EvenSteven. I learned that splice technique somewhere in Cretaceous Period as we were stringing the first Electrified Vines while working to keep the T-Rex out of our yards.

    The splice is really strong and takes tons of pressure to break.

  12. Bruce

    hmm, the western union I used for explosives the tails were longer, and we brought them back and wrapped them another three times around each other. Thats what gave them the lock.

  13. Beverly

    I now know even less than I knew before reading this manual. Typical government overexplanation trying to cover with way too little information.

    Never did see completed spliced.

  14. Big Al

    Years ago I heard this splice called “Western Union Splice”. They
    used it on Telegraph wires….. [Maybe back to the first Telegraph lines, 1860’s??]

  15. Forrest

    Someone better take a very close look at the diagram above. The termination of each end of the twist, on both ends, is going in the incorrect direction with respect to the direction it is shown as being started. Duh!.

  16. charlesd

    The 2nd pic is just from the other side.

  17. Forrest


    Follow the flow – not a chance – you don’t start the twist going CW and have it end going CCW – Put some in your hands and try it – you will see – NASA Mechanical Engineer, retired.

  18. bartman2589

    Perhaps it was originally called a “Western Union Splice” the article never suggested it was called anything really, all the article did was to point out that this method is the one that was adopted by NASA engineers, the article doesn’t say they renamed it, it doesn’t say they tried to claim they invented it or anything of the sort, it simply informs us that NASA uses this technique to splice wires together.

    @Beverly, the middle image IS the completed splice (just minus tape/heat shrink tubing and ‘optional’ solder flowed into the splice), the bottom image just shows the splice after soldering it (again without any tape/heat shrink tubing).

    I say ‘optional’ in regards to using solder because there are proponents that support using solder and those that recommend bare wire to wire contact citing that using solder adds resistance to the circuit (while this may be true, in most instances I’m willing to bet it’s a negligible amount of resistance and unless you’re working with very precise voltage/signal levels will likely not be an issue), even then you can somewhat minimize the introduction of resistance by using a good quality silver based solder. Also remember DO NOT use Acid Flux for electrical connections, Acid Flux is primarily for use in working with things like household copper water pipe fixtures where the water flowing through the pipe will wash away the excess flux, and of course DO NOT inhale the fumes from ANY soldering work regardless of the type of flux or solder used, often times they contain very harmful toxins that can lead to illness/organ damage.

    And Forrest is correct, whoever ‘shopped’ this got the end directions wrong in regards to the direction it wraps, other than that detail the images are a good representation of what you end up with using this method.

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