[time-nuts] DC distribution

[ed breya]

Larry and Bill have hit the nails on the heads. For crimping, it's 
important to achieve a gas-tight connection, by essentially cold-welding 
enough Cu of the wire to the Cu or alloy of the crimp device. Too much 
of the wrong other materials present, or insufficient crimping force, 
may produce weaker, less reliable joints, or rectifying junctions. 
Environmental effects can take their toll over time too, so the 
application and level of reliability needed should be  considered.

For good crimps, the materials should be clean, of course, or typically 
protected by thin plating like Sn or Ag or Ni. Some of the plating is 
displaced during deformation, and the fresh, clean Cu underneath becomes 
intimately bonded to that of the crimp device. Too little deformation 
won't provide as much fresh Cu to bond, while too much will damage and 
weaken the wire strands. The best crimps can be made with both the wire 
and crimp made of bare copper, and thoroughly cleaned just before 
crimping. This isn't very practical for routine use, so plated crimps 
are much more common, while the wire can be had in all sorts of varieties.

Even tarnished bare Cu wire and crimps can work, as long as the crimping 
action exposes enough good copper to bond, rather than just squeezing 
them together, possibly forming a copper oxide rectifier (remember 
those?). This doesn't matter much in power connections, but may 
especially in small-signal applications. Consider the lowly wire-nut, an 
insulated helical cone of spring steel, threaded onto two or more wires 
that are simply in contact, say in AC power branch circuits. These work 
just fine, if properly applied, left mostly undisturbed, and protected 
from the elements.

Ed