EN60204 and twin ferrules

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.

I think that it's rather a shame that the standards organisations don't publish (as far as I know) official clarification documentation after the publication of a standard which is (perhaps inevitably) found to be ambiguous, unclear or otherwise in need of clarification. After all, with the best will in the world it's a pretty tall order to make a standards document absolutely bombproof and perfect. Some would argue that the notion of producing a standards document (particularly those of a relatively complex nature like 60204) which does not need any further clarification is a overly ambitious endeavour.

A somewhat different stance seems to be taken by the European Commission in respect of the various EU Directives. Some while ago I obtained a couple of publications published by them: "Useful facts in relation to the Machinery Directive 98/37/EC" (266 pages) and "Comments on Directives 98/37/EC" (269 pages). I know these now relate to a supersede Directive but I assume that updated versions of the documents still exist. Both documents are immensely useful and packed full of explanations, clarifications and lots stuff which assists a mere mortal to become confident that he's done his (or her) compliance job adequately well. Similar documents (which could perhaps grow as clarifications were made) for 60204 would be a immensely useful (especially if they mentioned twin ferrules).

Knowing that the EU documents existed was part of my reason for my original post here. I was hoping that an official standards clarification resource might be offered up by someone.

Yes Jam of course it is, the size is for two wires, although these may be of differing sizes, but is generally the overall cross section. As the only terminal connection is to a single piece of copper (the ferrule) I cannot see how anyone could claim this is somehow TWO, conductors! I could of course join the two conductors to a single one away from the terminal with perhaps a solder sleeve, but this is clearly daft. Many "standards" have this kind of ambiguity, that is why BS7671 has quite a lot of definitions at the front, attempting to make it as clear as possible, and to reduce (nearly works) interpretation.

Weidmueller, amongst others, specify the min max conductor sizes specifically for twin conductor bootlace ferrules for use with their terminal blocks. Notably the sizing is sometimes different to that for singles, presumably because the ferrule is larger to accommodate the second conductor.

Thanks GTB - nicely summarised.

Dave in the shed,

I dont think you will get a definitive clarification etc. It is like thousands of other regs and standard items where it is down to one's interpretation. I think everyone on this thread is interpretating EN60204 and connections into terminals the exact same. Like you meeting an over zealous QA inspector that indicates otherwise is in my opinion reading the satement wrong. Two conductors are terminated correctly in the twin ferrule, and to comply only one "Conductor" the pin of the cable lug or twin ferrule is clamped in the terminal, the satement is about the terminal.

GTB 

Thanks again.

All useful examples of good reasons why the twin ferrule should be allowed to exist and not be banished to to the world of forbidden things that once were useful to sensible people. I think that I now have a pretty good armoury of reasoning to confront any ferrule jobsworth.

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....

I am not aware of anything published, but here are three ways of looking at this.

(1) Let's say that the double ferrule is at the supply end of a cable. The portion that is within the metal part of the ferrule is one conductor, albeit of, say 14 strands. The fact that it promptly splits into two each with its own sheath immediately afterwards does not change the matter.

(2) If you remove the ferrule from the terminal, how many conductors do you have? Answer = 1.

(3) If you carefully remove 20 mm of insulation from a cable, bend it through 180°, and insert it in the ferrule, have you suddenly made two conductors out of one. Of course not!

HTH and good luck!

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