Crimping Problems

Hello

I have been struck by how variable the results of uninsulated lug crimping can be.  This was initiated after crimping a lug on some 35mm2 SWA with a Hex crimping tool.  After crimping it was clear that the lug really wasn't that tight on the cable.  I normally use an indent type tool for smaller sizes and so far haven't had a problem but my tool tops out at 25mm2 hence the hex crimp.  


Googling leads to a range of horror stories and practices including crimping one size down which tends to produce ears on the lug reducing copper section by considerable margins which cant be desirable.


I have tried a range of different lugs from different sources and the results are really quite variable.  I know that the correct procedure is to use the crimp tool manufacturer's lugs and the corresponding dies but it seems to be both difficult and expensive to do so and I doubt that most of the smaller crimps  are done in the correct way.  My local wholesaler only carries one type of lug and I don't think the maker makes a crimp tool.  


I have spent some time measuring the 35mm2  lugs and tool dies with a  Vernier.  This is harder than it sounds as the lugs are not quite circular and not quite cylindrical.  Interestingly I get an average excess area of copper of only around 2% within a range -3%!! to 7%.  I have always thought that somewhere around  10% excess was required for the best electrical and mechanical properties.  The -3% does explain why the joint was pretty poor though.

This reference http://www.cable-glands-cable-cleats-crimping-tools.co.uk/BS7609-BS7727-British-Standards.htm has some interesting information including a chart which seems to confirm the 10% reduction.


In an emergency the best way forward seems to be careful measurement of lugs and dies and topping up the copper content of the crimp with a few carefully selected very short strands when I cant source a lug with thick enough walls.  


I understand that it doesn't matter within limits if the lug is loose on the cable to start with.  What matters is that the cross section of the copper in the lug plus cable is around 10% more  than the die cross section (and that the dies close completely).


It does however seem daft that there isn't wider cost effective availability of matching lugs and tools or and easy compatibility system (like the Red, blue, yellow for insulated lugs) given the likelihood that poor joints may run hot at least.  


What do you think or am I missing something?



edited to clarify and correct