In replacing a 15A circuit breaker found that one of the buss bars is getting very hot.
Before connecting, installing breaker only, buss bar is hot enough to heat up the breaker?
Probable causes? There are more breakers on one buss side, unbalanced load.

Loose breakers, possibly an overloaded buss. If your comfortable with a clamp on ammeter, check the draw on the panel. Balancing out the panel may be something you can try, but do the troubleshooting. How old is the panel?

What was the reason for changing the breaker? If the breaker got hot instead that could cause the buss bar to get hot and would take a little time to cool down before installing a new breaker. Check to see if any other breakers are hot.

I will investigate further... including clamp-on for amp readings. Note: The buss bar was hot before installing breaker. Thanks,

I measured amps on high side of 100A breaker: Two load readings Red: 35/28 and 55/40 amps. Don't think this is enough unbalance to cause heating up buss bar? Can someone conrirm? Also, is probable that any one of the breakers was defective, it would act as bad connection and cause the bar to heat up? Thanks

No, that's not excessive. And you may be correct about the breaker. Did the buss cool after you switched out the breaker?

We are back to normal temp and load conditions. Plan is to check panel and all the breakers and connections to see if we can identity the cause. Thanks for assist.