EN60204 and twin ferrules

The EN 60204 compliance is assured because a dual "bootlace ferrule" is exactly designed to make 2 single wires into a single item for the clamping screw. I think that the 2 wires part comes from bolt lockdown where conductors form a loop under a washer and nut. 2 loops are obviously not a stable arrangement. Bootlace ferrules are designed to hold the core of a fine wire cable together and to prevent damage to the fine wires, in something like a chocolate block type of connection. A double bootlace simply holds the fine wires of 2 or more (given suitable size) fine wires together so that they are all correctly aligned and clamped by a single screw. I have never seen this arrangement (given a properly crimped ferrule) fail.

As you can see above they come in big sizes, that one is 25mm2, and much better for tails than even the more flexible type as shown

Thank you David - the body of agreement continues to grow.

When you say that 60204 compliance is assured, is that based upon what your experience as a mighty fine engineer tells you in your own interpretation of 60204 or is it based upon some published official guidance that I've yet to locate? Not that I'm doubting your opinion of course!

I'm still slightly cautious because there does seem to be a minority who forbid the use of twin ferrules in the land of 60204 and I don't want to rely upon the occasional twin ferrule only to have a splendid bespoke machine rejected by an over-zealous compliance officer at a client's premises. If only there was some sort of official clarification which I could wheel out in such an eventuality. It strikes me that there is justifiable reason for the definition of "conductor" (as used in the 60204 clause relating to the 1 wire/2 wire issue) in the preamble of 60204 to be extended to refer to twin ferrules.

So much discussion about the humble ferrule - who'd have guessed....

David Stone said:

bootlace simply holds the fine wires of 2 or more (given suitable size)

Sorry David, I fully disagree with the extremely poor practice of trying to cram more conductors into a ferrule than it's designed for.

Definitely only 2 of the correct size in a twin, without deforming the plastic insulating entry sleeve (and hence putting pressure on the conductors). Note you MUST have the correct metal tube size for the combined csa of the conductors (not too big, not too small) - and that's what causes the issue with insulated ferrules.

Example - it might seem logical that 4 no. 1.25 sq mm conductors might be brought together into a 2 x 2.5 sq mm ferrule (and I've indeed no problem with the basic concept, as the ferrule metal tube size is perfect for the job). However, the overall diameter (including insulation) of a 2.5 sq mm H05V-K tri-rated conductor is 3.3 mm, whereas the 1.25 is around 3.15 mm.

So, you can immediately see the problem, that if the inside of the plastic sleeve is a rounded rectangle with internal dimensions around 3.5 x 6.8 mm, there's no way you can ever squeeze 4 no. insulated 1.25 sq mm conductors in there.

The 1 x 4.0 sq mm has almost the same metal tube diameter as a 2 x 2.5 sq mm ferrule, but again you will struggle to get 4 no. 1.25 sq mm H05V2-K tri-rated singles into the 4.8 mm internal diameter plastic entry sleeve. 


I could see how this might work with bare (uninsulated) ferrules, if you matched the tube size properly to the overall csa of copper, but some copper would need to be left showing between the insulation and the entry to the ferrule, otherwise again stress on the copper from the insulation is likely.

gkenyon said:

So, you can immediately see the problem,

After posting, I had the thought whether you'd ask if I'd ever seen any real-world issues with this?

Well, the answer is yes ... which is why I've looked into the ferrule sizes and copper+insulation diameter and have the data to hand readily.

A similar problem arises with wire constructions of larger than standard insulation thickness, such  as some hot condition rubber types.  Then we end up core stuffing  with extra strands to fill out to the size of a crimp terminal that suits the insulation diameter,

In reverse there are XPLE railway cables and PTFE aerospace cables with considerable thinner insulation for a given voltage than the PVC equivalent, and then the wire tends to fatigue break where the strands enter the tube, and the use of RTV as an anti-vibration snotted into the cup like an ice cream  is called up in the worst vibration cases. (helicopters or tanks ).  Basically the old needs to be  'suitable for the application' comes back to bite us.

Mike,

A similar problem arises with wire constructions of larger than standard insulation thickness, such  as some hot condition rubber types.  Then we end up core stuffing  with extra strands to fill out to the size of a crimp terminal that suits the insulation diameter,

In reverse there are XPLE railway cables and PTFE aerospace cables with considerable thinner insulation for a given voltage than the PVC equivalent, and then the wire tends to fatigue break where the strands enter the tube, and the use of RTV as an anti-vibration snotted into the cup like an ice cream  is called up in the worst vibration cases. (helicopters or tanks ).  Basically the old needs to be  'suitable for the application' comes back to bite us.

Mike,