Electronic – Most ideal wire termination for round screw terminals


My '60 Volkswagen Beetle uses a number of electrical components that are equipped with round screw terminals, like you can see in the picture below:

Electrical components with screw terminals

What is the most ideal wire termination for these type of terminals?

So far, I've been considering the followings options:

Soldering the end of the wire

Although it will keep the wires from fraying, it takes a lot of practice to deliver a consistent job each and every time. Also, soldering inside a car is far from ideal, especially in awkward spaces. Wire terminations are also almost never soldered in aircraft and motorsport applications, same goes for automotive manufacturers. Must be a good reason for that.

Crimping ferrule onto the wire

This seems like a good option and I believe the VW factory did this. However, the tools they used made a rather small indentation which doesn't seem very reliable to me. I can find proper crimping tools that make a square or hexagonal compression, but I worry about the contact area and possible resistance with these ferrules in those round screw terminals. Is this something to be concerned about?

Soldering ferrule onto the wire

This leaves the round shape of the ferrule intact, but, as said, there are many reasons not to prefer soldering for automotive applications.

Are there better options out there?

Best Answer

Note that if soldering wire ends and then clamping with a screw in a terminal block or connector post as seen in your photo then the majority of the wire end MUST NOT be soldered - even though this is common amateur practice and may seem to make sense. If the copper wire is solder filled so it is "solid" then the screw will compress the soldered bundle and produce a tight connection INITIALLY. However, over time the solder will deform and creep and the screwed connection will loosen and fail. For this reason, soldering wire ends is forbidden in electrical wiring codes. It is usually permissible to solder wire extreme ends only to stop the multistrand wire fraying, but the majority of the exposed end and all the portion that the screw contacts must be unsoldered.

Good quality crimping tools can produce long life reliable automotive connections. HOWEVER after market crimps are often unreliable. I have seen situations where essentially all aftermarket crimps on a fleet of vehicles could be expected to give trouble in due course.
Crimping and then soldering is more time consuming and ideally should not be necessary - BUT it works well.

Ferrules are good when properly terminated. You could try pull apart tests and try measuring voltage drop between ferrule and wire using a significant controlled current flow. A 12V battery charger may provide enough current for this. I recently measured about 5 milli-Ohms contact resistance across an XLR/ Cannon plug-socket connection at about 15A - not too bad for what is usually used as a microphone connector :-). I'h hope that a crimped ferrule would perform at least as well. Careful probing will allow you to measure voltage drop across the actual crimp.


Willem said:

I've found proper tools for crimping the ferrules. My main concern is that the square shape of the crimped ferrules is not a good fit for the round terminals. Do you think that resistance will be a problem with these squarely crimped ferrules?

I see those for sale on Amazon for $US309.50 (free shipping). At that price I'd hope that they'd sing, dance, fly and produce crimped ferrules suitable for any application. They may do some of these things :-).

POSSIBLE alternatives

Start with the surprisingly real LOOKING $US16.99 4 jaw Signstek Adjusting Ratcheting Square Ferrule Wire Cable Crimper Plier Crimping Crimp Tool AWG23-10 Orange

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Followed (in price at least) by the $37.89 Samyo Portable Professtional AWG23-10 Self-Adjusting Hand Ratchet Crimping Tool Crimping Pliers for Cable Ferrules RBW06 (Red) which has 6 jaws and MAY give a better result, or not.

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Followed by a whole range of alternatives of increasing price - and of possibly increasingly capability.

The 6 face Samyo looks like it MAY be worth a punt. Note cable capacities when comparing.