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Practical Wiring - Club Level: Installing Sheathing

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Installing Sheathing


00:00 - The process of sheathing is taking our bare wiring harness assembled into its basic structure like we have here, and providing it with a protective outer layer to help keep it isolated from the harsh environment in which it has to operate.
00:13 We do this using either raychem DR25 heat shrinkable tubing, or flexible expandable braid.
00:19 We do cover this process reasonably thoroughly in our wiring fundamentals course, but there are some key details you need to be aware of when you're working with a more complete wiring harness like we've got on the bench here.
00:29 Now the key detail to be aware of is the order in which the sheathing in installed onto the wiring harness.
00:36 Most wiring harnesses are going to have a central trunk section that is going to branch out into the smaller harness sections on either side.
00:43 One side being in the interior of the vehicle and the other side being in the engine bay.
00:47 This does mean that you really do need to think through the entire process before you cut your first piece of heat shrink tubing or expandable braid.
00:53 However it does usually boil down to a case of beginning with your largest centre most trunk section and working out to those smaller branch sections which is exactly what we're going to do in this instance.
01:05 Now in this instance we're going to be sheathing this harness with raychem DR25 and the procedure begins with us determining the size of DR25 we're going to need for this central trunk section.
01:16 So I'm going to take a quick measurement of its diameter.
01:21 Now this doesn't have to be incredibly accurate as that heat shrink tubing is going to shrink down.
01:26 We're getting approximately 22 millimetres there.
01:29 So that's pretty close to one inch.
01:32 Now raychem DR25 has a 2:1 shrink ratio and that means that the ideal unrecovered size for our central trunk section here, would most likely be two inch.
01:41 Two inch DR25 is actually pretty hard to get a hold of.
01:45 I haven't really found any aftermarket suppliers that keep it in stock.
01:49 The largest size that is easily available is one inch.
01:53 And that is actually the largest size that we have in stock here and it's what I'm going to use to slide onto the central trunk section and we're then going to recover it into place.
02:02 Now using this smaller size of DR25 is going to give us one slight draw back when we recover it onto our central trunk section and that's that it is going to recover quite tightly and that is going to limit some of the flexibility of this harness section.
02:15 However in this application this harness section does not require a lot of flexibility and it is also going to be supported by the larger rubber sealing grommet where it passes through the firewall.
02:25 So knowing the size of DR25 that we're going to need, we're going to have to cut it to a specific length.
02:32 This is where we refer back to our prepared documentation because that is going to tell us the length that the central trunk section needs to be.
02:39 And in this instance we've got the measurement here of 350 millimetres.
02:43 Now that doesn't mean that we're going to cut a 350 millimetre section of our raychem DR25.
02:49 Because we are going to use a section of raychem SCL at either end to seal and support the branch sections.
02:56 Now I like to leave around about half the diameter of the harness section that we're currently working with on either side of that branch section as that gives us enough space to organise all the smaller branch sections as they exit the branch point.
03:12 So we know we've got a diameter measurement in the centre of our main trunk here that is approximately 25 millimetres or one inch.
03:18 And we're going to subtract half of that from either end.
03:22 So that means we're going to end up cutting a section of DR25 that is 325 millimetres long.
03:28 So I'll get my tape measure out and I'll get that cut to length.
03:35 With our section of DR25 cut to length, we've now gonna get it installed into that central trunk section of our harness.
03:42 With so many smaller branch sections on either end of our harness, this sometimes can be a little bit challenging and in this instance, is gonna be compounded by the fact that we're using that one inch DR25 where a larger size might actually be the better choice if it was available.
03:56 Now there are a couple of tips and tricks that can make this process slightly easier if it's really being a struggle, what you can do is actually use some kapton tape to tightly bind all of your smallest harness sections.
04:07 And that's going to get them as small as they possibly can be and give you a more rigid structure to slide your DR25 over.
04:15 The other thing you can do is use a lubricant to really help you slide that DR25 over the harness.
04:21 Isopropyl alcohol can be a really good option for this as once you've completed the operation it will evaporate away cleanly leaving no residue behind.
04:30 So I'm gonna go ahead and try to get this central section installed on our main trunk and see if I need either of those aids to give me a wee helping hand along the way.
04:47 Now with it installed in the centre we can slide it back and forth as we're going to have to do that to fine tune the position of our branch points to ensure we've got the correct length of our smaller branches on either end.
05:00 So to do that I'm going to work from the interior end of the harness here, we're going to determine the length of one of these branches from our documentation and then we're going to slide that centre section to ensure that that branch is going to be the correct length.
05:13 So working from our ECU one branch here, we can read from our documentation that that needs to be 200 millimetres long.
05:20 I can measure back from the end of our wires, 200 millimetres and that's going to give us the point where our raychem SCL material is going to need to end.
05:29 We're going to have to slide our main trunk branch of DR25 back from that a little bit further though as when we sheath the ECU one branch in its own section of DR25, we're going to want that to come down the branch, leave a small gap to our main trunk section of DR25 to give us room to organise those branches but then we want that whole section to be encapsulated in that raychem SCL.
05:53 So I'm gonna go ahead and get that in place now.
05:55 I find a gap of roughly the same diameter of harness section you're currently working with to be a pretty good guide.
06:03 So in this instance we're looking for a gap of around about 25 millimetres.
06:07 Just gonna give that a quick measure and we are right on the money there.
06:11 So with that central trunk section of DR25 in the correct location, we actually gonna go ahead and recover that onto the harness now, as we don't want its position to move when we are sheathing the smaller branch sections at either end of the harness.
06:26 I'm gonna get my heat gun out on the bench and gonna go ahead and do that now.
06:39 So we can see we've got our main trunk section of DR25 recovered onto the harness there.
06:45 It is locked in place, it's not going to be moving as we are sheathing the smaller branch sections at either end of the harness which is going to be the next step of the process.
06:54 Now determining the size of DR25 that we're going to use on each of these sections is exactly the same as we've done here.
07:00 We're going to measure their diameter and then choose the largest size of DR25 that will still shrink down to tightly fit that harness section.
07:09 That's gonna give us that wall thickness and abrasion resistance that we're after.
07:13 Determining the length of DR25 that we're going to cut is slightly more involved.
07:17 We're going to look at the length of branch section that we have.
07:20 So for our ECU one branch that's 200 millimetres.
07:23 We're going to subtract half of our desired clearance at this end which we said was going to be 25 millimetres, so half of that is 12.5 But then we also want to leave a section of exposed wire at the end here as we are going to have to strip these wires, we're going to have to pin them, and that does mean we are going to have to manipulate them into the correct locations in that connector.
07:43 I find for an ECU connector like this, leaving around about 50 millimetres of exposed wire still lets us have a very very tidy looking harness but gives us enough length that we can easily get a terminal pinned on there and get the wires manipulated into the correct place in that connector.
07:59 That means we're going to have to take another 50 millimetres of that measurement and that's going to get us down to a section of DR25 that is 137.5 millimetres for this ECU one branch.
08:11 Take a quick diameter measurement of that and we will determine the size of DR25 that we're going to need.
08:18 So that's coming in at approximately 14 millimetres.
08:22 So if we double that and get to 28 millimetres, we're actually over the largest size of DR25 that we have available which is that 25.4 or one inch DR25, so that is the size that we're going to use for this section.
08:36 So I can go ahead and cut that length from our DR25 now.
08:43 With our shorter section of DR25 cut, we can install that onto the branch, and in this instance it's going to be much easier as it is a more appropriate size for the branch we're working with.
08:54 Get that down to where it needs to be and we can actually go ahead and recover that in place.
09:00 Once we've done that, the procedure is exactly the same for the rest of the branches on this end so I will go ahead and we'll measure those, determine the length that we need, I'll cut all those, and I'll get those recovered into place as well.
09:46 So with our raychem DR25 recovered onto our wiring harness, it's now time to undertake the last part of the sheathing process which is going to be recovering our raychem SCL onto our harness transition branch points.
10:00 Now one detail that did come to light as I was undertaking the DR25 installation process was that as we recover the DR25 onto all of the smaller harness sections that exit the branch point, the wall thickness of the DR25 does actually make that slightly larger than the main trunk section here.
10:19 This does mean that I had to install the raychem SCL before I continued on and recovered the DR25 onto the rest of the harness.
10:28 Just a detail to be aware of when you are undertaking your own harness build.
10:32 You do really want to be thinking that couple of steps ahead just to make sure you're still gonna have access to the part of the harness you're going to need to work on.
10:40 Now I've got our raychem SCL in place here and we are going to recover that onto this transition point.
10:46 The SCL is going to do a couple of jobs for us.
10:49 As we recover it, it's inner wall which is potting compound, is going to melt, it's going to flow out and adhere onto our raychem DR25.
10:57 This is going to seal that transition point and give it really good environmental protection.
11:02 As it cools, it's also going to become very rigid and because it is then glued to our DR25, it's going to give us really good strain relief at that branch point.
11:11 You will also notice that I've wrapped our branch section tightly in some kapton tape, just a little bit more support to get everything nice and tightly arranged there while we're undertaking that SCL recovery operation.
11:23 To help that SCL really adhere nicely to our DR25, I'm gonna take some 120 grit sandpaper and abrade the outer surface of our DR25 right where the SCL is going to sit.
11:35 So I'll go ahead and I'll do that now.
11:50 The very last step before we slide our SCL into place and recover it onto our branch section is we're just going to take a paper towel and a wee bit of our isopropyl alcohol and we're just going to clean that off.
12:01 It's going to get rid of any of the leftover particulates from abrading that DR25, and just make sure that surface is really ready for our SCL to bond with.
12:16 So with that nicely cleaned and prepared, we can slide our SCL into place, and head over to our heat gun and recover that down.
12:30 So our raychem SCL is now recovered onto that branch point.
12:33 It's gone nice and rigid as it's cooled and that's gonna give us excellent strain relief for that interior branch point.
12:39 We can see at either end here we've got a good sealing bead of that potting compound showing.
12:45 It's bonded nicely with our DR25, gonna give us that little bit of extra sealing, just that wee bit of extra strain relief which is something that we are always looking for.
12:54 Last step of mechanical strain relief there was popping a cable tie on the outlet of this branch point.
13:00 Just gonna stop any pressure being placed on any of these branch exit points, being able to pull that SCL apart.
13:07 The rest of the procedure is exactly the same as this.
13:09 We've got our boots in place, so I'm gonna go ahead and abrade our DR25, get those boots in position, and recover them onto the harness now.
13:34 So now we've got all of our SCL recovered onto our harness and that is going to complete the sheathing process.
13:40 Just having a look at the detail here.
13:43 WE can see on our branch section we've got a really nice even bead of that black potting compound sealing that SCL to the DR25 all the way around.
13:52 And giving us a bit of strain relief on the outlet of the branch where our smaller sections come out as well.
13:59 And of course that last piece of strain relief, just gonna be a cable tie here on all the branch sections, just giving us that little bit of extra mechanical strain protection.
14:08 So now we've got the bare wires of our harness nice and protected from that engine bay and that harsh automotive environment, we can continue on with the rest of the harness construction process.

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