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Practical Wiring - Professional Motorsport: Sheathing

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Sheathing

11.12

00:01 - Sheathing is the process of adding the final protective outer layer to the harness sections that span between our branch points and our connectors.
00:10 The aim of the sheathing is to protect the harness sections from abrasion, chemicals, and to a certain extent, heat.
00:17 To do this we use a specific heat shrink product made by Raychem called DR25 heat shrink tubing.
00:24 This tubing is different from more common heat shrink that you might find at an electronics supplier in that it remains very flexible once it's been recovered.
00:32 Which means we will not lose the flexibility that we've gained by using a concentric twist method when we've laid the wires into the harness.
00:40 Sheathing a section of motorsport harness is not different in any major way than that of any other harness.
00:45 In fact it can often be easier as the twisted construction makes it easier to feed our wires through the unrecovered shrink tubing.
00:53 By consulting our documentation we can determine the length of heat shrink tubing that we're going to need to cut, with the size of that tubing defined by the diameter of the harness section that we're sheathing.
01:04 Choosing the largest possible size of DR25 tubing which will recover tightly to fit the harness section will give you the largest increase in wall thickness and therefore the best abrasion protection also.
01:18 While the specifications of DR25 state that it will not shrink along its length, only its diameter, I have found some reduction in the length when it's recovered to the normal.
01:30 I usually add around 5% to the length stated on the documentation to ensure that the DR25 will be long enough and trim it back after it's been recovered if it's required.
01:41 We're going to have a look at sheathing our example harness section now.
01:44 And the first thing we need to do is determine that we have the correct size of heat shrink.
01:49 It is determined by the diameter of these harness sections here which from our concentric lay up design, we are actually going to know in advance.
01:58 In this instance the correct sizes of heat shrink are going to be 3/4 of an inch for our main trunk on this side of our branch point, 1/2 an inch for the continuation of our main trunk, 3/16 of an inch for our three sensor harness branches here, and 3/8th of an inch for our ignition wiring that's exiting this transition point at 90 degrees.
02:19 Installing he unrecovered heat shrink onto our harness sections really is quite easy with a motorsport harness.
02:26 I'll get my half inch section for this branch here, and because this is a twisted construction that's all nice and tightly contained, there's no errant wires flying off anywhere, it is going to be very easy to install this shrink tubing into place, which I'll go ahead and get done now.
02:44 Now there is a key factor that we need to be aware of when we're installing this shrink tubing.
02:49 And that is where it is going to end at our branch point here.
02:53 We are going to be booting this branch point in a shrinkable moulded shape, and we need to make sure that when we've recovered our DR25 shrink tubing, its end is going to be within that boot, and that's going to let us completely seal the harness.
03:08 To explain what I mean, I've got the documentation of the shrinkable moulded boot that we're going to be using here, and we need to make sure that our DR25 is going to end within this point here.
03:19 I do have a recovered mouldable boot shape here which just to drive the point home, if we lay on top of the harness, you can see that these are the points that we're going to be wanting our DR25 shrink tubing to be ending within, and then when we recover this into place, that we are going to be able to seal that to our DR25 tubing.
03:39 So that is going to be a good location for the tubing to end on this branch.
03:43 It's going to be similar for our three sensor sections here, and then we'll double check it again when we're installing the sheathing on the other branches.
03:50 We are going to go through in detail, the installation of these shrink moulded boots in another section of the course.
03:56 Now that I've determined the positioning of the DR25 there is going to be fine, what I'm going to do is get our heat gun heated up and I'm going to shrink the first probably 25 millimetres of this DR25 down and that's just going to lock its position in place while I'm working with the rest of the harness branches.
04:20 So I'm gonna go ahead and install our 3/16 inch tubing onto our sensor branches here and this really is nice and easy with these harness sections twisted together, as you're not having to deal with any errant wires flying out the side.
04:34 When I've got each of these installed, just gonna pop quickly back over to the heat gun and lock that position down before I move onto the next one.
04:40 That's also going to reduce the overall diameter of this end and make installing each piece a little bit easier as well.
04:58 With those short sections of our DR25 tubing recovered, it is setting the position of our DR25 tubing quite nicely, that's gripped onto the harness quite well there.
05:08 We are going to do two more steps before we go ahead and recover the rest of this tubing using our heat reflector.
05:14 I'm going to abrade the end of our DR25 tubing here where our heat shrink boot is actually going to make contact, as we want to get a really good seal on that.
05:25 Once that's done, I'm actually going to put some Kapton tape right around the end here just to really hold those pieces of tubing in place, make sure they don't move while we're handling the harness.
05:36 When it comes to abrading your sections of DR25 tubing, anywhere between 120 and 180 grit sandpapers, a nice wet and dry with a strong back I find works quite well.
05:48 You can actually get specific tools for doing this, it's a plastic moulded body that takes a sandpaper loop and that little bit of extra tool leverage does make it a wee bit easier to do the job but you can also get by with just a wee bit of cut off wet and dry 150 grit like I've got here.
06:06 I'll hold our recovered mouldable boot shape up to the harness again, just to show you really where we want to be abrading.
06:13 You can see where it lines up there, it's going to be in this area here, that we're going to want to abrade and I'm actually going to do it slightly past the end of where our boot will be as we want to make sure that we get a really good seal there and we are going to be using some epoxy to make sure we get that seal and that's going to give it somewhere to bond onto.
07:02 With all those DR25 sections now nicely roughened up and abraded, going to put some Kapton tape right here just holding those bits of DR25 to our branch point, making sure that they're not gonna move down the harness at all as we're handling it.
07:17 I did go to quite a lot of effort there when abrading those sections of DR25 to make sure I got onto the inside of all the sections.
07:25 And that is really important as when we put out potting compound into this join when we shrink that mouldable boot into place, it is going to need to seal to the inside of our harness sections here.
07:38 That's another pretty key difference when you're building a motorsport harness versus a club spec harness or a modified street car harness.
07:47 With that Kapton tape in place and our abrading done, that should have given our heat gun enough time to cool down so I can swap the attachment on the end for our heat reflector.
07:57 I'm then going to recover the rest of our harness sections here and I should be able to do those all in one go under that heat reflector and get them all recovered nice and tightly.
08:08 Really crucial point when you're dealing with heat guns there is that right after you're using them, the tip of that is going to be very very hot.
08:14 So if you need to change it out, just make sure you're careful.
08:42 Now that we've got our DR25 recovered into place, everything is nice and tightly gripping the wires underneath but we haven't lost any of that flexibility that we got from using the concentric lay up pattern.
08:55 The sheathing of the other branches is exactly the same process, I'm going to get my DR25 installed, confirm its placement at our branch point to make sure that we're going to be shrinking that boot down onto DR25 and the harness will be sealable at that point and then recover it into position.
09:13 So I'll go ahead and I'll get our other remaining sections of heat shrink onto these harness branches now.
10:35 Now that we've got our DR25 all recovered into place, you can see that each section is extending far enough into our branch point here that it's going to be completely covered by our sealing boot when that's then recovered into place and we've got everything nicely strain relieved and held in place with our Kapton tape.
10:53 As you can see, the sheathing process does not differ greatly when we are constructing a motorsport harness when compared to a street car or a club level track car harness.