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19 Nov 2019, 11:42

Wiring for Dummies

Years ago I used to run the motorcycle workshop “Wannabe Choppers” together with my son Enrico. We did a lot of customising and repairs. My responsibility was vehicle electrics and electronics. Many times I was confronted with disastrous results of hobbyist’s wiring, not seldom done by trained motorcycle engineers. During my time in the automation industry, I was often stunned by the perfect wiring in control cabinets. But again, when software engineers wired their prototypes, I often witnessed them making fundamental faults. So I thought it would be helpful for you to write down some rules for proper wiring.

Do not solder the ends of copper stranded wires!

Sometimes it is hard to get all strands of a stranded wire into the mouth of a clamp. But soldering the strands together (“tinning”)  is not the right solution for this problem. In fact, in the automotive industry, soldering wire ends is strictly forbidden. There are several problems with solder on wires:

  • Solder makes the end stiff. Vibration stresses the strands at the edge of the soldered region, which becomes a predetermined breaking point. When half of the strands have been broken, the electrical resistance raises and the power dissipation at this point may raise the temperature resulting in a cable fire.
  • Solder is a weak material compared to the clamp’s screw. Therefore a soldered wirehead cannot be fastened securely in a screw clamp. The connection will loosen, resistance raises and a hot clamp results in softening the solder even more.

Do use properly sized wire end sleeves together with a professional crimping tool!

Modern clamps do have a funnel-shaped mouth and can be used with stranded wire because the screw or spring does not directly crush down the strands. But pure copper strands underlay oxidation. A well-crimped sleeve or connector pin is like bonded material: No air reaches the strands because strands and sleeve are forming a massive unique “cold welded” object. If the sleeve itself is tinned, there is a minimum risk of oxidation.

But be careful: Some spring-type terminals are designed for unsleeved stranded wire and should not be used with sleeves. Do consult the datasheets!

To all “pre-generation-y” crimpers: Do use your glasses and proper working light!

The older you are, the less you will be able to see a single strand without visual aid. Twisting the strands before inserting them into the sleeve ferrule is not the best idea (you will never get a cold-welded connection when doing so). Without twisting the strands, you can easily miss a single strand while pushing them into the ferrule. This single wire strand could be the reason for a severe system failure when it touches a neighbouring contact. So be sure you will detect such a strand before you press the crimping tool!

Nothing is worse than a poor crimped connection!

Missing a single strand is just one type of fault and using the wrong crimping tool another. While a square shape crimp is the right choice for cage-type clamp terminals, the cheap gripper tools are pressing a U-shaped form which is critical for clamp terminals: They may bend the U flat again and thus loosen the wire. They also do not apply enough force to form an air-sealed connection.

You also need to carefully follow the instructions of the manufacturer about stripping length of wire insulation and insert depth of the wire to get perfect crimping results. When doing this job by hand, you better use a 1:1 drawing of these measures and compare it to your length. Do not rely on the print marks on automatic wire strippers for the correct length. Especially since crimp terminals and crimp contacts of connectors require a perfect wire strip length to also clamp the wire isolation for pull relief.

Do mark your cables and terminals!

Marking cables and terminals is not a luxury; it is crucial error prevention. I know buying the markers is a massive expense in the beginning. But it is worth it! If you are not able to spend the money, you may use hand made cardboard markers or just use a non-erasable pen. If you own a 3D printer, you should go for DS Mechanical and draw and produce your personal cable marker clips to clip them onto cables and enable you to fix a tag or to write directly on them.

Also, try using a standard colour scheme for your wiring. Besides certain norms for specific domains (e.g. automotive, control cabinets in industry, home electricity) many companies have their own extended colour schemes for wiring. Be aware that there is a considerable amount of people with colour blindness. So again: Do use markers!

Plan for maintenance!

If signal quality allows cable connectors, it is wise to use them instead of clamp terminals. Imagine the time you need to un- and re-clamp 50 wires instead of just disconnecting the cable’s connector. But think ahead: Will the connector also pass any clearance hole when you need to exchange the cable or anything fixed to it? Sometimes it helps to design different and put the connector on the opposite side of the cable to enable an exchange of a component.

These are just a few things I have learned while experiencing faults. Please feel free to add further ideas in the comment area. There is nothing more powerful than crowd experience!

Volker de Haas started electronics and computing with a KIM1 and machine language in the 70s. Then FORTRAN, PASCAL, BASIC, C, MUMPS. Developed complex digital circuits and precise analogue electronics for neuroscience labs (and his MD grade). Later database engineering, C++, C#, hard- and software developer for industry (transport, automotive, automation). Ended up designing and constructing the open source PLC / IPC "Revolution Pi". Today engaged in advanced development as a service.

19 Nov 2019, 11:42