how much power do you REALLY need during the outages? if you plan on running HVAC syst3ems and such you will need a standby genset, not a portable one.

I only plan to run two refrigerators, one water pump as needed, two light/fan circuits, and a TV circuit. A standby genset would be great but I can use the portable unit with the RV as well. I'm looking at a diesel operated unit as I have diesel on hand year round.

A 5KW will do well for all you mentioned but the water pump remains an uncertainty as I'm not sure what size/voltage/HP it is

keep in mind that most RV gensets are 120v ONLY. may/may not work for the pump.

Trying to get two structures with separate services to have some of their loads fed by a common generator is going to be mind bogling in complexity to do legally.

If I'm reading the OP correctly, this is more of a design and configuration problem than a generator sizing question. And given what you've said about your electrical service, it's an interesting problem.

But first, let's test some assumptions to make sure we're all understanding what you have to work with, as well as your objectives.

1. You mentioned a 320A meter pan, so I'll assume that means you have 320A service from the POCO. If so, and your barn is wired for only 60A, the house panel is probably at least 200A, and perhaps more.

2. In effect, you have two "main panels"--one in the house and the other in the barn. (This is mildly suggested by the bonded grounded/grounding conductors at each of the panels.) Beyond the fact that they both draw from the same meter, they aren't otherwise connected at any point and the barn service is entirely independent of the house. Is this correct?

3. I'm uncertain whether the house is fed by a four-wire feeder (two hots, a neutral plus a ground) or a three-wire run. That's a bit ambiguous when you say "ground(ground rod) and neutral bonded". Are there are separate grounded and grounding conductors running to the dwelling. Also of note: Are the two disconnects fused? (By fused, I mean a circuit breaker or fuse.) If so, what size?

4. Any more details about the locations of the loads you want to power? From the description so far, it sounds like the primary objective is the house. Given the size of the barn panel, I'm guessing there isn't a lot of heavy-duty farm/agricultural equipment there. Where's the pump and is it 240V?

OK, let's mull over some of the factors.

At 75 yards distance, the ability to use the existing feed to the house would be a big plus, costwise. That is, if you were to choose a design that ran a second line from house to barn, you'd probably be looking at something like 225-230' of #6AWG CU or #4AWG AL, neither of which are cheap. (At this point, I'm just shooting from the hip on wire size.) Then there's all that the trenching, etc.

The solution you're aiming at sounds like a strictly manual cut-over. That is, since you say you plan to use a smallish portable generator that will double for an RV, you won't be installing a large generator capable of starting up and handling "enterprise loads" automagically. (OK, that's a term I just made up to account for the "dual main panel" scenario.) ;-)

So, let's throw out a couple of strawmen.

Option 1:

Put a heavy-duty manual transfer switch at the disconnect to the house. The 120/240V generator outlet would then feed the whole house and, at the same time, an 120V extension cord or two might service a light or two in the barn. (This may or may not meet your requirements, especially if you've got a 220V pump out there.)

This would mean that to use the service in an emergency, you'd have to turn off everything in the house main panel, start up the generator, cut-over the transfer switch and then selectively power-up a few selected house circuits at the house panel. Without this kind of manual intervention, a small generator would immediately get bogged down to its knees.

This is probably your cheapest option.

Option 2:

Hook the generator to the feeds for both the house panel and the barn panel using two transfer switches: one at the barn panel and the other at the disconnect for the house. This might give you the flexibility for choosing to run either the house, the barn or both on generator power. (That might end up being a plus because you could do periodic generator start-up and testing of your backup system entirely within the barn without disrupting household operations.)

Once again, you'd need to power-up individual circuits judiciously.

[I'll leave the question of whether there is suitably priced "two-service" transfer switch on the market to others. It's beyond my experience. Ditto with the option of using one large transfer switch between a dual-lugged pan and the two disconnects.]

There are other options, at least one of which would involve running a separate emergency service feeder from barn to a subpanel in the house with a transfer switch there.

I hope others more knowledgeable than I weigh in on this post because, like I said, I find it an interesting problem. Hope you get some more astute answers!

Most of your assumptions were correct. The two feeds from the 320A meter panel are a 60A and 200A disconnects feeding similar sized distribution panels. The wires used to feed the house are (2-Hot)4/0Al and (1-Neutral)1/0Al. The loads I'm trying to feed are rather modest:
BARN:
Water Pump
One Light

HOUSE:
(2) Refrigerators
A few lights and fans
Fireplace blower

I definitely will use the loads as needed in the barn and house. ie I would only energize the water pump when needed. I'm guessing something along the lines of option 2 would be the best bet for.

I am not sure if I have the facts right but based on a manual transfer (this is what we do), I would suggest just installing a 400 amp manual, non-fused, service entrance rated transfer switch with an inlet to plug your generator into.
This way, you will be able to power your entire interior panel and have the luxury of using any circuit that you need.
The only things that you will have to leave off are the automatic loads like ACs, water heaters, etc.
Other than that, leave everything else on so that when you go from room to room, you will have lights, TVs, etc.
You will have to keep an eye on what is on but even if you would happen to overload the gen, the worst that would happen is that you would trip the generator breaker.

I would suggest just installing a 400 amp manual, non-fused, service entrance rated transfer switch with an inlet to plug your generator into.
This way, you will be able to power your entire interior panel and have the luxury of using any circuit that you need.

If the only objective here were to service the house main panel (interior panel?), I'd have no qualms with this approach, but it doesn't address the two-service configuration.

[Also, assuming the remote house disconnect is fused at 200A, then a lower-rated transfer switch (e.g., 200A) could be used below the disconnect. Note that the OP still hasn't confirmed that the disconnect is fused, but I think he's implying that. It makes sense that it'd be fused in order to protect the 4-ought AL wire feeding the house.]

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If, as is likely, that water pump in the barn is 220V, the simple 120V extension cord option for the barn doesn't appear to be a viable option so, yes, I think you're looking at a two-transfer switch design of some sort.

My hunch is that any kind of single switch designed to handle two services would put you into some really pricey industrial hardware, so it's probably a case of "two is cheaper than one".

To further flesh out Option #2, you could consider installing a j-box with a 120/240V generator inlet spliced to two ouput feeds--one to each transfer switch, located immediately downstream of the discos.

What remains to be vetted, to my way of thinking, is the issue of how the grounding system works with that three-wire feeder. I hope that one of the double-E's here comes along to weigh in on that because I don't feel qualified to give you a confident recommendation about how to bond (or not bond) at the generator itself.

I have two generators. The first is a Yamaha 3000W inverter generator. I keep my fridge, freezer, all my 110 lights, computer, TV's, aquarium, and ceiling fans connected to it during an outage and have no problems, but of course everything isn't running simultaneoulsy.

It will also run my whole house fan (about 6A) if I shut down most everything else, and it will run my water pump (115V 17A) with all other loads shut off, but it sounds like it struggles on start up. It will not run my microwave under any circumstances, but I can run an electric wok or george foreman grill if I shut down most other loads.

I also have a Generac 7500XL. It runs the above loads, but will run the pump without struggling and will also run the hot water heater, but not both at the same time.

My routine is to run the Yamaha most of the time and change over to the Generac about 45 minutes before bath time to heat the water, then cut off the hot water and run the pump to shower.

The reason I do it this way is because the Yamaha is VERY quiet and fuel efficient (It will run 12 hours on 3 gallons) The Generac is very rough and loud and burns gas quickly, which is a problem when gas is hard to find after a storm.

I know alot of folks who bought propane or diesel generators and regret it. During/after a hurricane, gasoline is MUCH easier to find.

I know alot of folks who bought propane or diesel generators and regret it. During/after a hurricane, gasoline is MUCH easier to find.

that may be a regional/local issue. around here the first thing you see moving after any storm that kills power is the propane trucks.

almost every gas station sells diesel, and many have gensets of their own now after a major ice storm back in the 90's closed most for 2 weeks!

being 200 miles inland we don't get extended outages form hurricanes, but due to 95% of electric being overhead we do get extended outages due to ice during winter. the propane companies MUST stay running as all the rural folks need it for heat.

Diesel is a great choice for farms that have supply tanks for tractors, farm or logging equipment. Not only do they typically have a large supply on hand, but they'll end up paying off-road prices, which can be a lot lower than the gas station pump price.

Note the poster's comment above:

I'm looking at a diesel operated unit as I have diesel on hand year round.

In a pinch you could use home heating oil to run your deisel.

My preference is a diesel unit, but based on the prices I've seen, I don't think it'll be a viable option. Even having off road diesel already on hand, the fact that a 15HP diesel unit operating at 3600rpm still doesn't justify the cost. I can by two similarly equipped gasoline units. This will be intermittent use so unless I find a great deal on a diesel unit, I think gasoline is my best choice(maybe even with a propane kit).

I'll bet you have a farm tractor. How about a PTO generator? No extra engine to keep going, and you could get one big enough to run more than just a few circuits.

Yes, it is a regional thing. I'm in Florida near the coast and most homes in my area are all electric, so propane is really only used for BBQ grills and RV's, and very expensive. After a hurricane the propane places are usually closed for days. The gas stations open right away, but the only ones that sell diesel are near the major highways. After a storm, downed trees and flooding close enough roads to keep me from getting to the highways, so gas is a better choice for me.

Many of the generators( including my Yamaha) are available or can be converted to run bi-fuel or trifuel.