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Enter the count of each M22759/32 Tefzel gauge in the bundle. Spec maximum finished diameters are shown under each size, so the bundle estimate errs on the safe side.
Length of this twisted section, connector to breakout. The calculator adds the extra wire the twist consumes so you cut long enough.
A concentric twist harness lays wires in rings around a central core, one wire in the middle, six around it, then twelve, then eighteen. Each layer twists in the opposite direction to the last, which is what gives a professional motorsport harness its round profile, flexibility and resistance to vibration. This calculator takes your wire count per gauge, works out how many layers you need and where the gaps are, estimates the finished bundle diameter, tells you how much extra wire each layer consumes in the twist, and picks the Raychem DR25 size that will recover onto it.
Wires in the outer layers travel a helical path around the bundle, so they need more length than the core for the same section. A tight lay on a large bundle can add 5 to 10 percent. The cut length column shows what each layer actually needs.
Between 8 and 12 times the bundle diameter is the usual range. Shorter lays are tighter and more flexible but consume more wire and are harder to keep even by hand. Ten is a good starting point.
Fill the gaps with spare wires you may want later, or a filler of the same diameter, so the layer sits round and the DR25 recovers evenly. Spares are cheap insurance on a race harness.
Yes, and most harnesses do. Put larger wires toward the core, keep each layer to similar diameters where possible, and expect to use a filler or two to get an even lay. The calculator sizes the bundle by total copper area so mixed bundles still get a realistic diameter and DR25 pick.
The bundle must slide inside the supplied diameter with room to spare, and the recovered diameter must be smaller than the bundle so the sleeve grips. The calculator applies both rules. If the bundle sits between sizes, go up and let the shrink do the work.
Planning the connectors too? Run the layout through our Souriau connector selector, and see the wiring resources for the Tefzel ampacity chart and DR25 size guide.
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