Found this article on why ferrules should be used on stranded wire. Worth a read . https://www.weidmuller.com/bausteine.net/f/7862/Weidmuller_Ferrules_White_Paper.pdf?fd=3 Executive Summary Thanks to its superior flexibility, longer flex life, and resistance to vibration, insulated stranded wire is the ideal choice for most panels. From both a physical and electrical perspective, however, bare stranded wire is a poor choice for connections. Stripped of its insulation, stranded wire quickly loses the coherence that provides its strength and resiliency. Once it begins to unravel, it is subject to breakage and corrosion that can produce overheating, short circuits, and connection failure, as well as cause serious safety issues. Ferrules can rectify this situation by giving stranded wire the qualities of solid wire where it is needed most, at the point of connection. Ferrules significantly simplify installation, improve safety, and diminish the risk of costly panel failure.