I'm trying to replace an older subpanel in a barn 200' from the main 200 amp panel. I have many questions; How can I get a 200 amp rated panel out in the barn, what kind of tap/connection would I have to use coming off 200 amp main, what size conductor would I need, is this even allowed by NEC?

Your questions pose several other questions I need answered to help you:

Why do you need 200 amp in the barn? What will the load be?

What is the load of the home fed by the exisying 200 amp panel?

How will you get the wires from the home to the barn? Aerial or underground?

What type of connection is at the main panel now?

I am back-feeding the barn panel with a generator who's manufacturer recommends connecting through a 2 pole 60 amp to a 200 amp panel for buss bar integrity. (I was thinking I could decrease the main breaker capacity so it can't draw too much from the house?) The load in the house is close to 100 amp max. The transmission line will be buried and the current extension is through a 2 pole 60 amp breaker. Thanks.

Back feeding a panel from a generator in the manner you describe is illegal and unsafe.

Either an automatic or manual transfer switch that will isolate the incoming utility feeder must be used in the circuit.

If you are using a transfer switch, get back with the details and we can go from there.

I am using type tested and UL listed equipment that does have isolation switches and will have utility approval for interconnection.

OK then back to your original question, what is your question?

Started replacing a 200 amp subpanel, tapping into the main, somehow.

Then to backfeeding a 200 amp panel with a 60 amp generator feed.

Now using utility approved "isolation switch". This is a manual or automatic transfer switch, correct?

Lay this out completely for me so I can determine what your actual question is.

I am now very confused.

Thanks

Sorry for the confusion, I'll start at the barn. Outdoor generator, automatic transfer switch inside barn, utility disconnect outside barn, back in barn with 60 amp 2 pole breaker, 200 amp panel, and then my questions arrise. Lets say I'm running #2 copper out to the barn, how to I come out of the main panel? I suppose my direct questions are; how do I determine conductor size from house to barn (buried in conduit) and how to I get that size of conductor connected into the house's main 200 amp panel? Lets say I'm running #2 copper out to the barn, how to I come out of the main panel? Thanks for your patience.

With the xfer sw out at the barn, what is going to be fed by the generator? Only the barn panel? Or are you trying to backfeed the main panel in the house.

Or is the ATS and barn panel being fed by the 60 amp #2 feeder from the main panel?

I need just a bit more detail on the path of current, what is going to feed what.

Thanks, bear with me we'll get there.

Thanks for your patience. The generator will at times be supplying the barn's needs and part of the house's as well, when at other times the generator will not be supplying anything to the barn, and again at other times the generator will not be supplying enough to the barn. The automatic transfer switch takes the output of the generator, sync's it up to the utility power and then connects the output of the generator to the barn's panel through a 2-pole 60 amp breaker. At that time the electricity would first be supplied to the barn for various requirements and if ouput exceeds the demand, will flow back to the house through undetermined size wire into the main 200 amp panel in the house via an undetermined method.:) Again in other scenario's the generator will not be operating and all electric supply will be from main panel in house.

An Automatic Transfer Switch switches between either the utility or the genset, nothing "sync's it up to the utility power".

The two power sources are completely isolated from each other, the true purpose of an ATS.

For this to work properly, the ATS must connect to the main incoming service feeders at the house, connecting to Line #1 on the ATS. The genset feeder also feeds the ATS connecting to Line #2. The load of the ATS then feeds the panel or panels.

I cannot see how you plan to have the ATS at the barn and feed the whole barn and only part of the house.

I attached a quick sketch of how the ATS needs to be arranged to interrupt and isolate the incoming utility.

Perhaps you can explain further on your statement:
"At that time the electricity would first be supplied to the barn for various requirements and if ouput exceeds the demand, will flow back to the house through undetermined size wire into the main 200 amp panel in the house via an undetermined method.

I hope my sketch helps you understand how this needs to be wired.