What does exert too much mean? There is a 5.6Ohm resistor in there - At 42V there will be a current of 7.5A going through that little resistor which will heat up quickly. They are not made to hold that constantly but just for the initial connection. If you exert it too much and the current flows through the resistor constantly it will obviously melt.
Edit: Sorry I thought exert meant to pull the plug - just looked up the word and it means something different.