Is it a 50 amp service?
If its not, it's loose connections = high resistance where the burn is. Resistant at location A does not cause a burn at location B. The problem is precisely where you see it.
A 50 amp service, if miswired at the source, can potentially overload the neutral. So long as it's correctly wired to 220v, the neutral carries only the DIFFERENCE between the two hot wire currents.
If the source outlet has both 50 amp sources at just 110v, the neutral will carry the SUM of the two hot wire currents. No outlet should be wired at 50 amp /110-120v but you hear occasional accounts of people who've encountered a "cheater" 50 amp plug.
