The entire overload box is potentially overheating. All three input lines are hot the this situation could be due to three loose or corroded lug connections inside, but it exists a possibility where there could be overload condition downstream causing this overheating observation. You should immediately determine if this downstream overheating condition exists or not, and if yes, it should be corrected and tested again. If this is not the case, unmount, check, clean, and tighten the three lug's connector inside the box. Perform anyway a post thermal inspection soon repairs have been achieved.
Français: connecteur électrique
Nederlands: electrische connector