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Wiring Fundamentals: Bundling and Branching

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Bundling and Branching

05.11

00:00 - Bundling and branching our wiring harness is the process of organising all our wires so they can reach the parts of the vehicle that they need to.
00:07 The harness also needs to remain tidy and be routed away from possible hazards like heat sources in the engine bay.
00:13 The decisions made around where a harness should be branched or routed, need to be dealt with on a case by case basis and they're covered in our practical wiring harness construction course.
00:24 The physical process and materials we use to bundle our harness, and branch it out, remain the same no matter where we are doing it however and in this module we'll look at how it's done.
00:33 As an example of the procedure we'll look at a section of wiring harness made up of a single 18 AWG power supply wire that is spliced out to four individual 22 AWG power supply wires.
00:44 These would connect to the injectors of a four cylinder engine.
00:48 We also have the four injector signal wires which would run back to the injector output channels of the ECU.
00:54 The aim of our bundling operation is to organise our wires along the length of our wiring harness.
01:00 And we do this by taping the wires together along the wiring harness at even intervals.
01:05 The tape we use for this is very important and it's a particular type called Kapton tape.
01:09 And we use it 'cause it's got a very very high heat resistance.
01:13 It also has really good insulation properties and it forms a barrier between the wires and the glue which is inside the dual wall heat shrink and that becomes very important during the sheathing section of the course which we will look at in the next module.
01:27 This tape is also very lightweight and that is great for a motorsport application but it does mean it can be a little bit fiddly to actually deal with and for that reason, I like to precut the sections I'm going to use and store them on the side of the bench for when I need them.
01:44 When we perform our taping operation, I like to start from a known branch point of the wiring harness.
01:50 So in this instance it's going to be our splice point.
01:52 And we work outwards from there, taping the wires together at around about every 200 millimetres.
02:00 I find that to be a pretty optimal distance as it allows the wiring harness to retain its flexibility but still keeps all the wires tidily organised.
02:10 So I'll just tape these wires up here.
02:23 We need to pay extra attention to our branch points.
02:25 And we ended up using quite a lot more tape on them than we do on the continuous sections of the wiring harness, as we want the branch point to actually become quite rigid as it provides excellent strain relief.
02:37 So each branch exiting this transition point will get a piece of tape right after the transition point.
02:46 So we'll tape this one up here.
02:50 And these pieces of tape will actually end up being hidden by our dual wall heat shrink when we undertake the sheathing operation.
02:56 So while you want them to be tidy, it's not completely critical.
03:00 So with the tape applied to this branch at the exit of the transition here, we can go ahead and apply tape once again at our 200 millimetre increments along the length of this branch.
03:12 So we'll do that now.
03:19 And from here we copy this process to the other three branches.
03:22 So we'll go ahead and do that now.
03:39 So with that completed, we've got our transition point and our four exit branches here, all tidily organised.
03:45 We want to come back to our transition point now and apply some extra tape to it as we need to make sure that it is completely strain relieved.
04:02 So with the branch point now completely strain relieved, we can take a closer look and it is important to note that it has actually moved this branch point down the wiring harness approximately 15 millimetres.
04:13 Now this might not initially seem like a big change but it's the relationship between all these branch points along the entire length of your wiring harness that's the critical factor in making sure it fits the vehicle nicely.
04:25 And if they've all shifted by 10 to 15 millimetres, by the time you get to the last branch point on the harness, you can actually have quite a large discrepancy from your original design.
04:35 I'll mention at this point that there is another bundling technique used during wiring harness construction which you might have seen, called concentric twisting and lacing.
04:43 This is an advanced technique, not necessary at the modified street car or club day track car level.
04:49 It adds a large amount of time to the harness construction process and requires substantial planning.
04:54 It quickly becomes very complex.