Control Logix Power Supply Keeps going bust - Need Help

I am facing a very strange issue with the AB hardware, specifically with power supplies.

The problem started when a power supply in a 4 slot chassis suddenly shut down after being in operation for around 4 hours, we took of the power supply relayed a new wire from breaker to the power supply, checked grounding and volts after checking all possible causes we thought it as power supply problem and replaced the power supply. Everything was back to normal again for around 4 hours and then that power supply was shot down as well. The breaker was showing a short circuit inside the power supply. The model of power supply is 1756-PA72/c.

I have check the grounding and the supply voltage. My assumption is that it could be faulty chassis.

Would appreciate if you guys can help me out.

Thanks in advance.

Is it too hot inside the enclosure?
Could be a module drawing too much current. I doubt it's the chassis.
Please give model numbers.

Hello Keith, I have changed the chassis and it is fine so far...the model numbers are L71 , EN2T, CN2R and RM2...I had a hunch when I was installing the new chassis....thimbles on the supply wiring were slightly exposed..could arching on wires cause short circuit...