Concentric twist - core changes after branch point

Hi!

My questions are:

1. Can the core switch after a branch point?

2. Is it okay if it becomes larger/smaller in diameter after the branch?

3. Can a layer contain 24 AWG TW pairs twisted with 18 AWG wires?

My situation: Before branch point it was suitable to use 4x24 AWG TW pairs, as it gave me ability to use 4x 12AWG wires and 4x24 AWG TWSH pairs in the 1. layer - no filler wires needed.

After a branch I've got reed of all the 12 AWG wires. Now the most suitable would be to change the core totally, having the 4x24 AWG TWSH pairs from the previous 1. layer, to the core now.

While, if it's possible, move the 4x24 AWG TW pairs from the previous core, to the 1. layer now and twist them with 18 AWG wires.

Appreciate Your help!

Best regards,

Damian.

Hey Damian

Yes you can absolutely change the structure after a branch point and it is actually quite common. As long as the layup is physically achievable and stays within reasonable specs like lay length overall diameter and flexibility you can rearrange the core and layers as needed.

The reason cores often stay the same for the whole loom is simply that the longest circuits tend to be things like crank and cam signals which use shielded twisted pairs. Those naturally make good core conductors so it often makes sense to keep them as the core the whole way. But if those circuits branch off earlier then other wires will need to form the core further down the harness and the layup can change quite a bit from that point.

Mixing 24 AWG shielded twisted pairs with 18 AWG wires in the same layer can still be fine, just keep in mind the shielded pairs will be quite a bit larger in diameter than the single conductors so you need to make sure the layer still packs neatly and stays stable. It can be helpful to cut some short lengths and try a quick test layup to see how everything settles before committing to the final structure.

Also make sure the lay direction of the layer is opposite to the twist direction of the pairs. This helps stop the pairs from losing their twist or accidentally integrating other conductors if unshielded.

What you are proposing sounds perfectly reasonable 👍

Thanks a lot for Your kind answer! Assurance appreciated, as I am doing this for the first time =)