Electronic – Should I tin these wires?


I have to insert some wires into several electrical connections and have been getting conflicting information on whether or not they should be tinned before inserting. I'm sure this is a quite simple question to answer with a picture so I have included one below.

To be clear, the screw itself does not make the connection here, but pulls the flat conducting plate on the bottom of the connection toward the flat conducting plate on the top.

Regardless, the connection is still supposed to be a friction fit held together by the force that you apply from tightening the screw.

I suppose the root of what I'm unsure about is whether making an electrical connection under mechanical pressure would suggest you should not tin the wires or if it is specifically the rotation and grinding on a tinned wire that would be caused by the screw that makes tinning these wires a bad idea.

I'm obviously no expert on this topic so any additional explanation on the thought process behind the answer is very welcomed.

enter image description here

Best Answer

Tinning wires for these terminals has a couple of disadvantages:

  • The contact will be more tangential to the cylindrical profile resulting in a smaller contact area than if the wires were untinned and allowed to squash into a more rectangular shape.
  • If, for any reason, the joint gets hot the solder can start to soften, flow slightly and terminal pressure will decrease leading to further exacerbation of the problem.

On many industrial installations the wires will be pin-crimped before insertion. This reduces the risk of stray strands left out of the terminals. Some crimpers result in a square cross-section on the crimp and these work well with the flats grips on the terminals.