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Ferrules or fork-crimps in screw-clamp terminals
Udtwmc
12 Posts
Question
Currently in a dispute with a customer over bootlace ferrules I have used in screw-clamp type terminals - this is an industrial control panel designed to BS EN 60204-1, the wire used is class 5 tri-rated.

The customer says bootlace ferrules are the wrong type and wants them changing to fork-type crimps, arguing that the screw-clamp applies even pressure on fork crimps and a better contact but not so when ferrules are used - if you can picture the bootlace-ferrule on one side of the screw- with its clamp being at an angle as there is nothing on the other side of the screw. However, the termination is tight and makes a good solid contact with the ferrule so I think this is perfectly acceptable.

While I wouldn't generally disagree with a customer, there are hundreds of terminals to change, they didn't specify fork-crimps at design stages and I don't interpret anywhere in BS 60204-1 or BS 60947-1 that ferrules are wrong in screw-clamps.

Any opinions much appreciated.

 
9 Replies
davidwalker2
161 Posts
Hate to say so, but I think your customer is right.  I would not use bootlace ferrule on screw clamp terminals.

David
Udtwmc
12 Posts
Thanks for your reply. Do you base that on a standard that you know of or just personal judgment, experience?  i.e. do you have good evidence to back up why bootlace ferrules should not be used in screw-clamp terminals? I haven’t found anything as yet so am keen to know if there is. 

if it were a few terminations I wouldn't hesitate to change them just to ‘keep the customer happy’ but we’re talking 50% re-wire of a panel that they had many opportunities to change during various design reviews. 

thanks again. 
Zoomup
2724 Posts
Crabtree once had an M.C.B. design that could accept a single outgoing copper wire, say of 2.5mm2 on just one side of a small plate that had a central screw. I never liked the design as a small movement of the cable could loosen the grip on  the solid copper wire. With a stranded wire with say 7 single copper strands a 3 to 4 split could be made to try to even out the pressure on the wires.

We normally only use ferrules on fine stranded wires.

I like the idea of a flat forked crimp lug. What likely current will the crimp be required to carry?

Will vibration or door opening be likely to cause a terminal failure with a ferrule type connection?

Wire Ferrules Explained: Why are Ferrules Used and How are Ferrules Crimped - YouTube

Z.
mapj1
3413 Posts
I suspect it rather depends on the design of the terminals - some have a 'wobble washer' arrangement with a shaped washer under the head of the screw. These are intended to allow the terminal to accept widely different diameter on either side of the screw (or as in this case, none on one side ) and still grip firmly as the shape of the washer allows it to rock to form a clamp. What you do not want is the washer and the metal bed surface to form a wedge in the direction that the clamping pressure tends to drive the wire out of the wedge - it should either close parallel or slope to drive the wire towards the screw. Anti-rolling grooves in the bed surface can be used to similar effect.
This sort of thing will not be in the standards, (I;d be surprised if it was in anything to be honest) but the makers of the switches and so forth that have those terminals ought to be able to advise on the largest diameter they can be loaded to on one side only.
It may be  worth noting that with the very few remaining designs of telephone junction boxes that make use of  screw terminals, they are all designed to work with both single sided and double sided wire under the heads - BT at least accept wires under one side only..

Mike.
Whilst I would agree that the fork terminal would be a better option, as this would allow an even pressure on the terminal, there is also nothing wrong with using the ferrule option.

This sounds like a typical personal preference rather than a regulation issue, and if the specification states no preference, you should not  have to change them at your expense.

On a positive note, at least you used a crimp of some form, as i am surprised at the amount of installations, where no ferrules or crimps have been used
Paul Skyrme
156 Posts
I have done panels for many clients over the years and I have never seen a requirement for fork connections rather than bootlace ferrules in a screw clamp connection.
The panels have been supplied to global blue chip clients across many industries without issue.
I would never snag this on a panel whether working for the equipment manufacturer or the buyer, unless it was in a specification document.
Unless it is written into the signed contract I would be telling the client to jog on.
I have yet also to see a screw clamp terminal on a device that the device manufacturers state as unsuitable for a single ferruled class 5 or 6 conductor.
If it’s a machine panel then 60204-1 will take precedence over 61439 anyway.
Designing and building to 60204 meets the LVD (EESR) anyway.  Where as the 61439 series does not meet the requirements for the MD (SMSR).
When it comes to it effectively the two pieces of legislation are mutually exclusive.  It’s a declaration to one or the other for final piece of machinery.  Which obviously has to be the MD/SMSR, as the LVD/EESR do not cover machinery, but MD/SMSR, covers the requirements of the LVD/EESR anyway.
 The only reason why you would have to change, apart from placating the customer is if the connected device OEM states that a single ferrule is not acceptable in their product.
There is nothing in standards that requires a fork in a screw clamp connection.
Sounds like it's just a preference. In these situations I think it's better to turn it round and ask the customer to provide evidence that it's against the standards. You ought to check manufacturers data sheets first but I think it's unlikely that there is a problem.
Udtwmc
12 Posts
Thanks for everyone’s input here, much appreciated and good to know mostly we’re in agreement. 

I did check the data sheet albeit in a panic after I was challenged! Thankfully it does say to use ‘stranded or single core’. The person who challenged me happens to work for a highly respected blue chip company so had me reeling a bit. My mind is now rest assured though....He can jog on! 

 

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