A colleague sent over some photos yesterday of a small fire that had occured at one of the electrical connections on a ELCI breaker device he had sold to a customer. The photo below shows the aftermath of the small fire and the melted plastic around the terminal.
The terminal above got really hot!
This whole thing all centers around something I've said here many times before: "The primary by-product of excessive electrical resistance is HEAT". In this case enough heat to start a fortunately small fire. So what caused the excessive heat here? Simple. Check out the next photo, it tells the whole story:
The "stacked" crimp connectors were loose, creating excessive elecrical resistance.
The idea here is that whenever you need to affix more than one terminal on a single screw or stud (limit 4 max according to ABYC) you need to fan the terminals out so that they are NOT stacked as shown. The stacking will always trick the installer because the screw or nut will feel tight but in reality isn't and it will leave a gap as you can clearly see between the two terminals. This in effect reduces the electrical surface contact area for the connection and depending upon how much amperage you are trying to push through, will generate heat. The moral here? Fan don't stack multiple terminals on a single screw or stud.