Starter solenoid problem

I have changed 3 solenoid starters out in the last 3 yrs and put in new starter. Put in new starter and new solenoid yesterday and it worked4 times like brand new. Started the 4th time and the solenoid stuck and tried tapping like usual but didn't work this time and started making such a racket that I thought it was going to blow up. By the time I turned off the key it stopped. Then started smoking and I lifted the hood and by the time I removed the neg battery cable, it took about two min, and during that time it had melted the starter cable right off the solenoid and also melted part of the starter cable and the plastic had melted off the positive cable. Any feedback would be appreciated. RHO