When installing wire nuts to electrical wires, please make sure you tighten the wire nut good and tight to the wires. If not you will have a headache of a circuit not working later and or a potential of fire in the electrical box.
Here you can see a wire nut that the wires were not connected tightly and caused the wire nut to melt. Luckily the home owner smelled the burnt smell and turned off the breakers. We cleaned up the wires and installed a new wire nut.