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Practical Wiring - Professional Motorsport: Branching

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Branching

10.15

00:00 - The points where our harness needs to branch tend to be the most complicated sections to construct tidily.
00:06 Often we will strike a situation where a branch will contain wires from mulitple different layers of the harness section from which it is branching out of and this can make it difficult to tidily gather those wires together to form our new branch.
00:21 Our aim is for all the wires to be able to head off down their required branches without seeing any strain at the branch point.
00:29 This can mean wires needing to twist around from one side of the harness to exit out the other and resultantly can end up looking a little untidy.
00:37 While we should strive for the bare transition point to be as tidy as possible, the reality is that it will almost always appear a little untidy.
00:46 And what we really need to strive for is every wire being strain relieved.
00:50 Which we will accomplish with a combination of Kapton tape, our sheathing, and our booting materials.
00:55 Our harness sections between branch points will not change in construction along their length.
01:01 The number of wires will remain the same and all those wires will remain in their layers.
01:06 The same cannot be said for branch points however.
01:09 Our branch points are going to be thoroughly strain relieved and typically booted in a rigid mouldable, shrinkable boot.
01:15 We take advantage of the strain relief at these points and use them to make the necessary changes to our harness construction.
01:22 The two most common examples of this are reorganising our layer structure to account for wires that have branched out and any splice connections that we might need to make, most commonly a larger power supply wire, splicing out to smaller wires to supply individual components.
01:38 Or a CAN bus branch making a connection to the main bus trunk.
01:42 To show a typical example of how a harness might branch out, we'll have another look at our example harness section that we've previously designed and built, however we have partially deconstructed it now.
01:53 We'll branch this harness section out into five individual harness sections, exiting the main branch in two different directions.
02:01 Our engine position signals and our knock sensor signals will continue along the main harness trunk.
02:08 However our ignition wiring which was in the next layer up, needs to exit at a 90 degree angle.
02:14 Additional to this, three of our sensors, intake air temp, engine fuel pressure, and manifold pressure, will also need to branch out at this point, however they are going to branch in the same direction as the rest of the main harness trunk.
02:28 The rest of the wiring will be continuing along the main harness trunk and will be concentrically twisted around our existing core.
02:35 The first step of the process is going to be to loosely gather our wires into the branch sections they're going to need to be in.
02:43 For this, things to tend to get a little bit messy, particularly if you're dealing with a complete harness that might have much longer sections of wire.
02:51 But you do just need to work around that mess.
02:53 Using cable ties to keep things as organised as possible is how we're going to mitigate some of that problem.
02:59 I can quite easily identify our ignition wiring here as we know that that was in the first layer up from our core.
03:07 So we can get all that and get it coming out of our branch section here at a 90 degree angle quite easily.
03:15 I'm simply going to use a cable tie to hold that in place, a fair distance down that branch point as I am going to want to manipulate this point and strain relieve it in some Kapton tape and I don't want my cable tie to get caught up in that.
03:34 Additional to our ignition wires exiting at 90 degrees here, we do have those three sensors that are going to exit this branch point in their own harness sections, however following in the same direction as our main trunk.
03:47 So I'm going to have to separate out those wires now and we know that we've got a temperature sensor and two pressure sensors.
03:54 So that's going to be a pair of wires there for our temperature sensor, three wires for either of our pressure sensors.
04:09 With those wires separated out, although they are going to form their own individual branched sections, I'd probably cable tie those out of the way, all together as it will tidy up the rest of the wiring that's going to head along our main harness trunk, then we'll come back to these, organise them into their own individual branches.
04:30 Now at this point it should be pretty obvious that our concentric lay up pattern that we were using in our original harness section is no longer going to be valid.
04:39 As we now have our original core but we don't have that first layer of our 20 gauge wires, we've only got our 22 gauge wires heading off in the same direction.
04:48 So at this point in your concentric lay up design you would have actually designed this section of the harness with a different lay up, that these wires would fall into.
04:57 Of particular note in that design would be that our 22 gauge wires here, are no longer in layer two of our harness, they're in layer one.
05:06 So they've moved down a layer and that actually means their directional twist is going to change as well.
05:12 This is what we meant earlier on when we were talking about our branch points being nice strain relieved points that we use to make the changes that we need to make to our harness construction.
05:22 This is the point where we can change the twist direction of these wires as tidily as possible and then ensure that the harness section heading off down our main trunk here is going to be uniform along its length.
05:34 So I'm going to cable tie the rest of our wiring nice and tidily out of the way here along with our main harness core, as we know that this is going to end up wrapped around that, and we can get back to our branch points here and sort those out tidily into their individual branch sections.
05:51 Clipping our temporary cable tie out of the way here.
05:56 Of course being nice and careful that we don't nick any of those wires underneath.
06:00 We can now separate out into our individual branch sections.
06:03 So we have two pressure sensors and one temperature sensor but what that really means is that we've got two groups of three wires and one group of two wires.
06:13 In that situation these branch sections are going to end up just twisted around one another.
06:19 So we can simply branch them out individually and secure them with a wee bit of Kapton tape which is exactly what I'm gonna do now.
07:06 With our individual harness sections exiting the branch point now isolated, we need to arrange them in the orientation that we've designed them to be in.
07:15 By that I mean that we will have designed them to exit that branch point in a particular order to make sure that none of those harness sections need to cross over one another as they head to their individual components.
07:29 As an example of that, we'll look at our three wires here for one of our pressure sensors.
07:35 If for example we needed this particular harness section to exit over this side of the harness, so that would be in behind our 90 degree exit for our ignition wiring here, we would simply just twist this around and get that to where it needed to go.
07:51 You will notice this does look a little bit less tidy now, however what we're really aiming for is for everything to be nicely strain relieved and for there to be no tension left on those wires.
08:02 And the way that we are going to guarantee that is with everything in the right orientation now, we're actually going to wrap this entire branch point with Kapton tape.
08:10 This is gonna serve two purposes, it's going to help strain relieve it, so we know it's gonna be reliable, and then when we sheath this section, and recover our moulded boot shape onto it, it's going to protect the wire from coming into contact with the adhesive lining, that's gonna make future repairs possible.
08:28 I'm gonna go ahead and get this entire branch point supported with some Kapton tape now.
08:32 When you're using the Kapton tape, you will notice that it's actually not particularly flexible and as we are going to be wrapping it around corners, it's not going to lay nice and flat.
08:42 Don't worry about that, you just wanna make sure you have complete coverage, as you really want to be sealing those wires away from the adhesive that's going to be on the inside of that shrink boot.
09:09 You'll notice that I've kept out Kapton tape within quite a confined area there.
09:13 And that is for a very specific reason.
09:15 The moulded shrinkable boot that we are going to be shrinking onto this in a later stage of the course, has a specific measurement and we need to make sure that we keep all of our supporting Kapton tape within that.
09:28 The particular boot that you're going to be using in your application will have documentation that will let you know these measurements.
09:34 This example should show you that while we are striving for our bare branch point to be as tidy as possible, it's not like a twisted harness section where every wire has a defined place before we begin.
09:45 The strain relieving and sealing our Kapton tape gives us, goes a long way to smoothing out the branch point, as well as giving us the barrier between the wires and the sealing adhesives that will be used when the point is booted during final assembly.