Been tinkering with electronics at a hobbylist level for about eighteen months now. Revisiting some of my initial products and trying to bring some of my wiring up to standard. As I'm getting more involved, I want to do things the 'right way' - meeting some basic standards so at least I have a yardstick to compare my work to. Could anyone help with these questions?
1. What is the best way to terminate wire from an IEC lug connected to mains? I have a screw-in IEC socket into a project box. I read somewhere on this forum that it is acceptable to 'hook-in' the wire to provide mechanical support and then solder on. I assume something like an insulated spade connector wouldn't be appropriate because it may come loose with mechanical stress or say movement of the device?
”IEC lug” is a bit of an unclear description, since the mating side of the connector is what conforms to an IEC standard, not the termination on the inside.
IEC connectors most commonly have one of several terminations (and I’m sure others exist too):
- solder lugs
- spade terminals (Faston)
- screw terminals
- PCB pins
- insulation-displacement terminals
I’m assuming your question is whether you can solder to Faston spades: yes, you can. You solder the same as to a solder lug: Strip the wire, pretin it, form a hook using round-nose pliers, and then solder it in.
But I’m not sure why you assume Faston connectors are no good; they’re widely used for this, which is why IEC connectors with those spades are common. The only caveat I’d give, and it’s an important one, is that the terminals must be properly crimped. This means the correct tool of decent quality, used with a good quality terminal paired with the correct size of wire. So no tool or terminals from AliExpress or Amazon.
Note that crimped connections are generally more reliable with regards to mechanical stress and vibration than soldered connections.
2. Said IEC connector may be attached with metal screws to the plastic Jiffy box housing. These screws could become conductive if a fault condition arises, so I assume it is best practice to earth the screws?
That’s one solution. You could, for example, instead put heat-shrink tubing over the screws and nuts inside. Or use nylon screws. Or use a snap-in jack instead.
3. Does anyone have a clear explanation for the differences between identifying class 2, 5 and 6 cable?
The word “identifying” here is throwing me off a bit.
If you’re asking what the classes fundamentally mean, it’s simple:
Class 1 is solid wire
Class 2 is “rigid stranded” wire (containing two subgroups, “stranded” and “multi-stranded”, see the table linked below)
Both of those are typically used in fixed installations only.
Class 5 is “fine stranded” wire, the most common type of stranded wire, commonly used for both fixed and portable/moving applications. This is what typical flex cable is.
Class 6 is “extra-fine stranded” wire, which uses extra-fine stranding to give higher flexibility. Used only where this flexibility is needed and justifies the higher cost. Unlike classes 2 and 5, class 6 has a much wider range of possible conductor stranding. (For example, a 0.5mm2 class 2 wire is 7 strands, class 5 is 16-19 strands, but class 6 is anywhere from 28 to 256 strands.) For things like test leads, you really need to look at the stranding more than the class.
If you’re asking how to identify a wire’s stranding class (as in, forensic investigation), you cut it open, count the number of individual conductor strands and measure their size, then compare to a decent table (like
this one from Kabeltronik) to see what it matches.
If you’re asking how to identify a cable when choosing one to purchase, any decent vendor will state it on their datasheet. Either explicitly as a conductor class, or implicitly by listing the conductor stranding.
The big exceptions can be cables that comply with the harmonized cable codes, since a given cable code defines what kind of stranding it uses. See e.g.
https://www.tme.com/us/en-us/news/library-articles/page/41461/designation-of-cables-according-to-harmonised-standards/Common power cord flex is H05VV-F, which is:
H = harmonized
05 = 300/500V (i.e. 300V single-phase, 500V three-phase)
V = PVC conductor insulation
V = PVC jacket
F = fine wire for cables (class 5)
4. I have also read it is best practice to use crimped ferrules on stranded wire when placed under a screw terminal.
Absolutely. In many places this is required by code. But even where it isn’t, it’s highly recommended. Not only does it eliminate dangers (like stray strands shorting to adjacent terminals), it also makes using the screw terminals much easier.
In this case, is it:
a. ever used with mains power outlets (e.g. flush-fit ones on said project box)…
Absolutely.
…or is it acceptable to twist, trim and fold in half?
In many places, no, that would not be allowed. But as I said, regardless of whether it’s allowed or not, I strongly urge you to use ferrules.
FYI: Under no circumstances should you tin the stranded wire with solder before inserting it into a screw terminal. Solder cold-flows under pressure, so even if tightened firmly initially, it will loosen with time.
b. Would you ever use a ferrule on stranded wire before say using it for an Anderson powerpole 30A connector? I have always just placed twisted wire in an Anderson connector and crimped it with the appropriate tool, but wondered whether using a ferrule first is a better way to prevent loose strands or an imperfect crimp?
No, you would not normally do this. There’s no real advantage over just cleanly inserting the wire into the crimp contact. And adding another 3 layers of dissimilar metals (the ferrule base metal plus the plating on both inside and outside surfaces) certainly introduces more variability into the process.
The only exception, sorta, is if you need to “bulk up” an undersize wire to fit into a larger crimp contact. I have done this before, but only for signal lines which carry practically no current. (I did it recently for insulated crimp forks, to get 0.25mm2 (24AWG) wire into forks intended for 0.5mm2 wire, because I do not have a crimp tool for 0.25mm insulated terminals. But it is just for the 24V input signal to solid state relays, so only around 20mA.)
I would also only ever consider doing this on a closed-barrel crimp. DO NOT use a ferrule on an open-barrel crimp, since the two conductor crimp “wings” are supposed to grab onto half of the strands each and grip them. (For the same reason, don’t twist the wire tightly before inserting.)
Note also that you aren’t really supposed to twist the wire before crimping. That reduces the reliability, apparently. Moreover, a tighter twist increases the diameter. With ferrules, and especially with extra-fine stranded wire, it’s possible to twist enough that it won’t fit into the correct size ferrule, which might lead one to go up a ferrule size. High-reliability wiring standards (like NASA and military) expressly prohibit twisting the strands, other than to carefully restore the wire’s original strand lay, if it gets disturbed during stripping.
If you have trouble with wire being difficult to insert, practice and improve your wire handling techniques: learn to be gentler, and use tools that are gentler. For example, using cable shears to cut wire preserves the stranding lay much better than diagonal cutters. Diagonal cutters crush the wire rather than slice through it as shears do.
If you’re getting “imperfect crimps”, and you’re sure your technique is sound (= correct contact size for the wire in use, with the correct tool, using the correct jaw opening for the combination of wire and contact size), then you need a better crimp tool. My experience with crimp tools is that cheap ones (from AliExpress/ebay/amazon) do not produce consistent crimps, due to poor manufacturing tolerances, poor design, and the lack of a contact locator (a positioner that holds the contact in the correct place) and lack of a wire or insulation stop (a thing that ensures the wire is inserted correctly, by providing and end stop that either the strands or insulation run into, depending on the design). In contrast, a proper tool will produce one perfect crimp after another. (Last week, I crimped 100 contacts each of Molex Micro-Fit and Amphenol Ecomate, using the correct official tools, and did not have even one imperfect crimp.)
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