Unfortuantely, this sort of thing is a regular problem, and really a design flaw rather than anything users are doing.
I think the basic problem is that historically RepRap boards don't use connectors that are rated high enough. Of course, higher rating means bigger connectors and more expense, and people rely on anecdotal test like "I ran it for a bit and it didn't get hot". But the point is the rating is for a worst case, if you have a low ambient temperature and free air, then it will be fine. If it's stuck in a box with poor airflow, then eventually it overheats. Also people subsitute cheaper parts without checking the rating.
Additonal problems is that the screws can shake loose, but also the wire creeps in the clamp especially if soldered. This leads to higher contact resistance.
So really you want to make sure you have connectors with a good margin, plus use crimp ferrules and ensure the connectors are not affected by shaking. Improved airflow also helps.
The spec for the Phoenix MSTBA connectors says 12A, so that operates on the limit for a typical heatbed. The TE equivalent rating is 15A, for cheap Chinese sources probably more like 8A. The plug and socket connectors are convenient, but tend to have a lower rating than a straight screw clamp terminal.
If you replace the connector, get a quality part from a reliable source like Digikey etc, with a rating that exceeds the required current.
I think the basic problem is that historically RepRap boards don't use connectors that are rated high enough. Of course, higher rating means bigger connectors and more expense, and people rely on anecdotal test like "I ran it for a bit and it didn't get hot". But the point is the rating is for a worst case, if you have a low ambient temperature and free air, then it will be fine. If it's stuck in a box with poor airflow, then eventually it overheats. Also people subsitute cheaper parts without checking the rating.
Additonal problems is that the screws can shake loose, but also the wire creeps in the clamp especially if soldered. This leads to higher contact resistance.
So really you want to make sure you have connectors with a good margin, plus use crimp ferrules and ensure the connectors are not affected by shaking. Improved airflow also helps.
The spec for the Phoenix MSTBA connectors says 12A, so that operates on the limit for a typical heatbed. The TE equivalent rating is 15A, for cheap Chinese sources probably more like 8A. The plug and socket connectors are convenient, but tend to have a lower rating than a straight screw clamp terminal.
If you replace the connector, get a quality part from a reliable source like Digikey etc, with a rating that exceeds the required current.