Tidy your wiring - Embedded.com

Tidy your wiring

I was told that back in the 1950s when a British Post Office technician had completed a telephone installation (unlike North America, the Post Office was responsible for telecommunications in most of the British influenced world), the foreman would check the wiring layout with a spirit level. Much later, in the 1990s I saw a technician wire a panel with a layout so orthogonal it was truly a work of art. With the cost of labour today (even before the 90s) wiring has become much more unruly, but whilst a bird’s nest may be OK in a prototype, production and maintenance must have a systematic and manageable wiring configuration. In order to produce low cost houses rapidly in South Africa, they have a standard house layout and then drop a pre-made wiring loom into a house shell from above and in a few hours the house is completely wired. Some of us actually do have to take our assembled boards and drop them into panels and interconnect them in the field. This discussion is for you.

One of the earliest techniques of bundling wires together was to wrap the wires using a catgut-like twine. When trussed up tightly it looked good, but it wasn’t very flexible and more importantly, any change involved cutting the twine and then rewrapping. Cable ties are an extension of this idea although the sheer number of different types and colours of cable ties can boggle the mind. Take a look at Essentra’s e-catalog. It does help to use a cable tie tool to tension the cable ties. In one of my earlier blogs “Top 17 helpful hints for constructing electronic systems” I gave a hint that bears repeating. If you are going to cut a cable tie, cut the block with the locking mechanism. If you try and cut the band itself, there is an incredibly good chance you will cut one of the wires as well. One commenter pointed out an occasion where there was a thin fluid pipe in the bundle, and someone cut through it necessitating a complete rewire.

I am not sure about recent vehicles (who looks under the hood these days), but spiral wrap was very common in automobiles at one time. Using a special tool, it is easy and quick to work, and can be combined with twine or cable ties. An alternative to the spiral wrap is “split corrugated loom tubing” and is easy to stuff the wire into the tube since it is split along its length.

If you need liquid-tight sheathing there are alternatives, but you are going to need techniques to pull the wires through and the patience of a saint, or a wiring department or subcontractor. And if you really have the time, to make the project pretty you could fish your wires though a woven sleeve. You can even get it in silicone or fiberglass for high temperature applications.

With the wire in looms you may want to attach them to a panel or some other surface. There are many ways to do this using cable mounts and latching clips as well as clamps. Feast your eyes on the selection that Richco provides and see how easy (sarcasm) it is to make a selection. And they are only one of many manufacturers.

Figure 1: Cable loom with cable ties and self-adhesive mounts on the front panel (Source: Author)

Figure 2: Flat cables held by flat cable mounts. (Source: Author)

For projects where you want to hide your cables completely you can use surface raceways or so I am told. This is not dissimilar to the tubing used to carry household and industrial electrical wiring. It comes with T sections and corners. Sizing and cutting will require some accuracy and I expect some kind of automation for repeat orders.

I am more familiar with ducting where the duct consists of a channel and a cover and the sides of the channel are fingered so that wire can be brought out of the ducting close to the point of contact. It is possible to use cable ties inside the duct, but not really necessary as the wires are hidden by the cover.

Figure 3. Ducts with the wires feeding out to connect to nearby devices. Note the cable glands on the lower right. (Source: Author)

Now if your loom is attached to a moving assembly there is the chain cable carrier system which is a flexible duct system. It would be nice to design something with this one day.

You have to remember to cater for the fact that the cable must pass through the side of a panel and must be protected from chafing against the sharp metal edges. There is the simple grommet edging or from my perspective, the better option of strain relief (aka cable gland) so the any external tugging at the cable is not transmitted to the connections inside the box.

And finally – labelling the wires. There are several systems for wiring labels. The more dated approach involved preprinted markers that cater for a particular wire diameter that you slip over the wire one marker at a time to build the identity. There are also self-adhesive pre-printed characters on cards that work in a similar and you have to stick each one in turn onto the wire. I really dislike this approach. More modern systems use printed adhesive tape á la the Brother P-Touch that allows any text and almost any length. Brady is probably the best known in this field.

I have provided links above to individual suppliers for all the parts. There are many alternatives and substitutes, some of them direct replacements. Any electrical supplier will carry a full range. Did I leave anything out? Do you use any other techniques, or do you use any techniques at all. Let me know in the comments below.

Editor's Note: Do you have examples of particularly good or exceptionally bad wiring? If so, send Max Maxfield or Steve Evanczuk a photo (jpeg, please) with a one- or two-sentence description along with the source of the photo (as Source: xxx) – see examples above – and if it's your own photo, just use your name as the source.

2 thoughts on “Tidy your wiring

  1. “As a comment to his blog “Do They Know that “Analog” Makes Digital TV Possible?”nhttp://www.planetanalog.com/author.asp?section_id=396&doc_id=564478&nBill Schweber points out a link to good and bad examples of cabling:nnhttp://www.cablinginst

    Log in to Reply

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.