I have just removed my electric shower due to the front getting warm.When i removed the front cover i discovered that the terminals to the actual water heater were discoloured and melted slightly,i am going to replace the shower with a new one but would first like to know if this fault lies within this shower unit or is the problem elsewhere.The shower is a 9.5kw and have been told by an electrician the the wiring from the fuse box to pull switch to shower unit is ample.
Yes the cross sectional area of the cable is important. If the electrician says it is ample then use it again but with one proviso:
Hopefully you will have some spare cable to pull through because you will have to trim back the cable until you find nice shiny conductors. because the terminals have been damaged by heat they may no longer carry as much current as they used to and this will cause them to overheat again.
It shouldn't cause you too many problems as you could always position your new unit slightly lower and gain some cable that way.