I Can't Get A Break

[printbus]

I agree with Mjolinor. This looks like the heat bed wires just didn't have a good connection at the screw terminals. The bad connection(s) led to higher resistance than normal, and the higher resistance led to heat dissipation that softened the terminal block and made the connection worse. The bulging of the terminal block in the DSC_0001 picture tells me the heat was coming from the screw terminal. Other than the deformation of the terminal block, the rest of the board is likely fine.

In other personal and professional efforts, I've used terminal blocks like these but I don't really care for them. For a given terminal block, they work better with larger gauge wire than they do with smaller gauge wire. The ones here are better, but some also seem to be designed for use only with solid conductors, not stranded. Here's my approach to ensuring good connections to this sort of connector. These recommendations would apply to both types of connectors listed in gmay3's link to the RAMPS parts list.

• If you have the option, go with larger wire gauge to provide more copper volume for the terminal to grip.
• When I'm stuck with a wire gauge that is pretty loose in the terminal, I'll usually strip twice the normal length so I can fold the end of the wire back over itself. This doubles the gauge of the wire the screw is binding to. I've had some extreme cases where I've folded the wire end more than once.
• Strip the wire carefully. If you cut or appear to nick any strands in the stripping process, cut off the damaged end and try again.
• After stripping, I usually re-twist the wire but that may be arguable. This will help prevent strands from not going into the terminal or strands that aren't gripped tightly by the screw. If the end of the wire is being folded over, fold it after the twisting and use a pliers to squeeze the fold tight.
• Be sure that enough wire insulation was removed so that the insulation is not entering the terminal connection. The screw can't grab the copper properly if the insulation is in the way.
• Don't tin the twisted wire. It's fine for the strands to have been tinned by the wire manufacturer. If the twisted wire is tinned, the solder will creep over time and slowly weaken the screw connection. EDIT: Here's a reprap wiki post regarding this - http://reprap.org/wiki/Wire_terminat...crew_terminals
• Tighten the screw firmly, but don't over do it.
• Inspect your work. Make sure there are no loose strands that didn't go into the terminal and that the wire insulation is clear of the terminal. If you can see it, make sure the wire passes under the screw, not off to the side where it may not be gripped as well.
• For loose cabling like wires to the hot end and heat bed, add a cable tie-down somewhere to minimize any wire movement making it to the terminal. Wire movement can shift the copper strands and weaken the screw connection. The part of the wire without insulation is already a weak spot in the wire; any movement there can stress the wire and lead to strands starting to break.
• Maybe a day or a week later, go back and retighten the screw terminals. You'll likely be surprised to find the connections are looser than you left them. For those that have tinned the twisted wires, it is especially important to go back once in a while and retighten the connections.