What are some of the causes of this? Not enough amps for the 220?
Lots of possible causes in my experience:
People who think a kiln and a home clothes dryer are the same and just plug in to an existing X amp circuit.
Electricians that think they know better than the kiln manufacturer or the kiln installation folks and say they can save the homeowner some money by doing it THIER way.
Poeple who wire it themselves and know just enough to be dangerous.
Corrosion in connections becasue of improper installation or improper routine maintenence. Corrosion increases resistance to eletrical flow.... resistance to flow equals heat being generated... heat being generated where is it is not expected equals disaster.
Installing a new kiln supply in a REALLY old panel , and not having the whole panel checked out at the same time. (The new circuit is fine.... the old main supply connection is the issue. See corrosion.....and cobwebs.)
That's the basic list. Neil....... your input?