I doubt that harmonics are a problem on relatively small and single phase loads.

I also doubt that a distribution system fault is to blame, no common or likely fault would increase the supply current, but not trip the overload protection.

Probably poor connections leading to simple ohmic heating. Either poor workmanship by the installers, or poor manufacture of devices resulting in poor internal connections. Possibly not helped by frequent overloading and repeated re-setting. Damp may have corroded connections and resulted in heating.

I doubt that harmonics are a problem on relatively small and single phase loads.

I also doubt that a distribution system fault is to blame, no common or likely fault would increase the supply current, but not trip the overload protection.

Probably poor connections leading to simple ohmic heating. Either poor workmanship by the installers, or poor manufacture of devices resulting in poor internal connections. Possibly not helped by frequent overloading and repeated re-setting. Damp may have corroded connections and resulted in heating.

We have mused this sort of thing before, and wondered last time for water heaters I think.. Unless the supply loops through the incoming terminals onto the next it is hard to see how more heat would be created in live than neutral - presumably they are within 30mA of each other...
So we have to conclude the heating curretn is similar but cooling is not as good, either because the layout of the cables in the box is assymetric, or because inside the device that terminal has less metal attached to it to act as heatsink.  I do expect the two sides to be different, as in the RCBO, the live connects to the current sensing part with its heater and coil, the neutral has a contact and passes the sensing coil.
It may be an age thing, but I preferred traditional terminals with round cable tunnels and double grub screws - a rectangular cage only sort of hits where it touches, and that is not really an all-round contact.

M

Why is the RCD dirty?  Could there be enviromental factors

mapj1 said:

It may be an age thing, but I preferred traditional terminals with round cable tunnels and double grub screws - a rectangular cage only sort of hits where it touches, and that is not really an all-round contact.

You could say that about many terminals, but the non-moving side of the terminal is often concave. At least modern terminals do not deform the cables. I suspect that the CSA of contact, especially with smaller cables, is often greater than the CSA of the cable.