[TowerTalk] Crimped Electrical Connections

[Howard Hoyt]

Hi all,

I went through this process working with broadcast and recording studio 
power systems and contacted Panduit to get recommendations.  They said 
there are at minimum three different and often more types of crimp lugs 
for any given wire gauge which vary for bore size, wall thickness and 
lug material.  For stranded wire there are lugs for THHN type stranding 
(7x, 19x, 37x strands) and a different lug for fine stranded wire which 
can have up to 20% more copper by cross-section than the THHN stranding 
of the same AWG.  The lugs for solid wire crimping are designed with a 
different alloy which has a higher crush force and the crimp barrel is 
longer.

Crimping can be separated into two types:
1) Light duty hookup wire #16 and smaller use bent-up sheet metal lugs, 
which form a light duty crimp which captivates the wire but does not 
form a cold-weld.  In general the current being passed in these small 
gauge wires is low enough so the fact that the connection is not 
cold-welded will not cause heating or excessive voltage drop.  The 
connection will not however be gas tight and will degrade over time as 
the connection corrodes if exposed to humidity or salt spray.

2) Wire gauges #14 and larger are best made using compression lugs.  
When properly executed the goal is to achieve what is called 
cold-welding where the lug and wire fuse in a gas-tight cold weld.  To 
get a quality cold weld the crimp barrel of the lug must be clean and 
free of oils and the wire must be clean and free from oxides.  Cutting 
through a properly crimped lug the wire strands can be seen to have 
fused to the lug and will not fall out.  Good quality lugs have a brazed 
seam, but the best lugs are deep-drawn from special alloy annealed to 
the desired temper.

My own experience with inexpensive imported lugs from eBay and 
Aliexpress is they have thin walls (made from standard copper pipe?) and 
do not retain the crimp pressure and loosen easily.  I have seen 
overheated connections using these lugs in starter-motor usage with a 
simple dimpled crimp.  The better lugs made by AMP or Panduit are much 
tougher and thicker walled and I have never had one heat up or fail and 
they are much more expensive, but you get what you pay for.

The other issue is having the proper crimp tool for the specific lug, 
and this is critical.  I purchased a hydraulic crimp tool from Zoro 
which had a wide range of changeable hex tooling dies and found none 
were quite right to give the specified crimp for Panduit lugs.  In the 
end I found doing a partial crimp, rotating the lug 60° or 120° and 
finishing to full pressure gave the specified results.

With a cable assy which is subject to any movement or vibration I would 
never post crimp solder, in a robot application I have seen those crack 
from where the solder wicked down the strands inside the PVC jacket 
leaving the jacket intact.  Indeed a properly made cold weld will form a 
single mass and there are no air gaps for solder to wick into, so it 
adds no extra value.

Cheers & 73,
Howie / WA4PSC