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To twist . . . or not to twist . . .

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nuckolls.bob(at)aeroelect
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Posted: Sat Oct 19, 2013 2:58 pm Post subject: To twist . . . or not to twist . . .

 	  Quote: 	
		   	
 

    At Hawker-Beech we had automated wire cutting, marking,

    stripping and termination machines that produced thousands

    of ready-to-install wire segments a day. None of these machines

    had a 'twisting' function. The as-stripped strands were

    immediately fitted with the appropriate terminal and

    crimped.



    A review of NASA-STD-8739.4 for the fabrication of wire

    bundles and terminations, I found no example for terminating

    wires were either single or multiple wires were twisted

    by the installer before attaching a terminal.



 [img]cid:.0[/img]



    I've never witnessed such a practice by technicians nor am I aware

    of a rationale for doing so.



    In fact, the 'wire nut' designed for wiring of buildings

    achieves gas tight connections at the corners of a square-

    wire, conical-spring. As the device is twisted

    over the ends of parallel strands, the cone expands and

    crawls up and over the ends of the cut strands. 



    An early example of this technology was not insulated.

 [img]cid:.0[/img]



   A conical spring wound of round wire and fitted

   with a 'handle' was simply wound onto parallel

   strands. The counter-wind torque expanded the

   spring up and over the strands thus increasing

   the pressure that kept the wires in good contact.



   Later versions deleted the handle, added insulating

   cap that also served as a handle . . .



 [img]cid:.1[/img]



   They also wound the spring with square wire having

   a corner turned in. This sharp edge would bite into

   the strands of wire thus increasing both mechanical

   grip for running the spring onto the strands AND

   increasing the numbers of high-pressure (gas tight)

   joints between conducting elements of the connection.



   None of these products would benefit from a pre-twisting

   of the wires before installation. Standard practice calls

   for twisting the cap on until the strands DO twist slightly,

   say 1/2 turn or so. This is your installation limit indicator

   that the spring is no longer climbing onto the wires and

   further rotation serves only to twist the bundle which

   adds nothing to the quality of the finished joint.



   Therefore, the short answer for any kind of installer-

   twisting of strands in a wire or wires in a bundle

   seems to be "not necessary and possibly deleterious

   to the finished joint."



 

   Bob . . .

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Robert Reed

Joined: 22 Oct 2009
Posts: 331
Location: Dallas/Ft.Worth

Posted: Sat Oct 19, 2013 5:09 pm Post subject: To twist . . . or not to twist . . .

The only exception I can point out would be if anything should cause stray strands to separate from the bundle.



Bob Reed

Sent from my iPhone



 	  Quote: 	
		   On Oct 19, 2013, at 5:56 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:

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