In the world of electrical power it's important that all connections be made securely. It's gotta be tight (not so tight that you strip threads off bolts/screws) to prevent high resistance contacts which will create heat.
Soldering of power connections (where practical) helps to alleviate any future problems however simply having proper torque with all strands in a connection point will be satisfactory.
Here is an example of a 220volt air conditioning unit power plug. The unit worked flawlessly for 7 years until one day it stopped cooling. When the power plug was pulled away from the 220volt wall outlet, one blade remained in the receptacle.
Why did this happen? The wire connection to that plug blade was not properly done and resulted in a high resistance point. Over time with the AC compressor cycling, the heating and cooling of that improperly made connection point got the issue worse. The wire itself began to burn. This is an example of a potential fire hazard due to bad wiring connection!
How could have this been detected earlier? A simple tug test on each wire when the plug was made up would have revealed an insecure connection. Also a thermal camera would have picked up a hot spot issue had one been made available for predictive maintenance. Even voltage measurements (where practical) on the load side of a connection will reveal any problem.
Step 1: Fixing the Plug.
Even though the wire is burnt not all of it needs to be condemned. An easy way to find a good usable portion of the wire is to cut back a bit (in this case I cut back 6 inches) and make a knife cut around the insulation. If it slides out easily (not being fused to the strands) and it's flexible and not discolored, the wire can be used now.
Again proper torque on the blade screws and ensuring all strands are inside is a great way to have it done. Doing a tug test per wire is highly recommended.
Step 2: Replacing the Outlet and Faceplate.
Since the original outlet and faceplate received thermal stress from the fault, it was necessary to replace those. The wiring in the outlet box was not damaged and installation was straightforward.
Now the air conditioning unit is working fine and future predictive maintenance will be applied.