I fix some machines for a living that use fuses or breakers rated 20
amp. Its pretty common for fuses to physically overheat and blow from
poor connections heating excessively. breakers trip the same way.

see switch wires melt from the same situation.

plus breakers are designed to become MORE sensitive as they age.
learned that westinghouse used to make breakers and I fixed machines at
their plant in beaver pa.

fascinating place