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Ferrules or fork-crimps in screw-clamp terminals

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.

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0 mapj1 over 4 years ago

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.
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0 mapj1 over 4 years ago

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.
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Ferrules or fork-crimps in screw-clamp terminals

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