Have fed pacific 100 amp main [rh13100 na ni ] that gets hot when ac,washer&dryer are all on,just started to trip main ?

Rich, This may sound obvious, but either the main breaker is acting normally because the load is near 100 amps, or it's defective. If it seems that the loading conditions have not changed from prior years, then you have probably been close to the 100 amp level before and a small amount of corrosion has occurred over time (accelerated by the heavy loading). The cleanliness and tightness of connections is critical to carrying loads at rated capacity. If you are close to the rated load, then replacing the main will buy you some time (but probably not as much as the original because the bus bar connection to the main is probably slightly corroded too) but it won't solve the problem - you will need to upgrade to a higher amp service. On the other hand, if you can calculate or measure the total load and you aren't near 100 Amps, then you just need to replace the main. One other thought. If you have a significant part of the load that is not 220V, then it you might have a higher load on one phase than the other, and could possibly be remedied by switching phases on some of the branch circuits. You only have to exceed 50 amps on one phase to trip a 100 amp main. Good luck, Al K