"An example would be a furnace. The burner is screwed to the case which is bonded to the blower motor EGC and threaded to the gas pipe."
I have worked on a number of residential furnaces where there was no solid connection between the burner assembly and the furnace itself. The burner assembly just sits in brackets, without screws or other mechanical bonding. In this type of equipment the furnace EGC, does not provide a good bond to the gas piping.
Don
