I have a manual transfer switch that was installed approximately 10+ years ago that is rated 5000 Watt and 20 amp max input. The old generator died and was replaced with a Generac GP5500 / 6875 model. Twistlock outlet from generator states 120/240 vac - 30 amp. Wiring to transfer switch is 10 - 3 w/ground - approximately 60 foot run. Transfer switch has 6 - single pole 15 amp circuits with two connected together for well pump. Others are for fridge, furnace and lights. Should this transfer switch be upgraded or is it safe to operate?
From the information you have given out on your last comment "maximum 5000W" the answer would be that you need to replace the transfer switch to match the new generator.
Your old transfer switch (xfrs) has a max rating of 5000W and you new generator actually has a surge wattage of 6875W which is considerably more than the existing xfrs rating. We are not taking into consideration what is connected to your current system. It's a matter of how much the generator can provide. In short you size generators to provider a certain amount of power. You use what's connected to calculate the required size not the other way around.