OK, before anyone smacks me, Let me say that I'll use an interlock (two in my case). But here's my question and why a transfer switch doesn't seem to work for me.

All the houses in our area have 400A services. They split it at the meter base and run feeds to two 200A panels mounted right beside each other. We have mostly gas appliances, so we don't need the juice, but all the panel space is nice. Anyway, I only have a 6KW generator, but I'd like to be able to feed anything in the house if needed. Important things are the fridge, freezer, sump pump, well pump (the generator is big enough as long as I don't run much else at the same time), pumps for the septic system and the furnace blower. Unfortunately they aren't all in the same panel. So unless I get a hugely expensive (and complicated) transfer switch that can handle 400A split between 2 panels (not even sure how that would work), I'm left with backfeeding the panels.

Here's my plan and I'd like any input or ideas- keeping in mind that this will probably only be used once every couple years.

Mount a 30 or 50 amp 240 breaker in each panel (set up with an interlock to the master breaker) and feed it through conduit to a box with a matching (30 or 50 A- Just planning ahead in case I get a bigger generator some day) receptacle- one for each panel. Then I can just use a heavy 10Ga cord to connect the generator to one of the input receptacles. It means I can only run one panel or the other at a time, but for how little it happens, I'm OK with that.

Anyone have thoughts, suggestions or better ideas? Anyone know if a regular 30 or 50A breaker can be backfed? Or do they make a special breaker that's rated for backfeeding? It's a GE panel. Thanks.

I can't see any fundamental reason why you can't backfeed both panels from a single generator input cord as long as the mains on the panels are interlocked with the backfed breakers.

This is no different than a single 400 A source splitting into two 200 A panels.

Since the panels are net to each other, once the mains are off, you have the option of turning on one panel, the other one or both.

Remember that the generator should have the neutral/ground bond removed when connected to the house.

Why make things more complicated than it need be?

Thanks for the input. I was thinking that I would have two separate sets of interlocks/breakers/input receptacles- one for each panel- that were totally independent of each other. But am I understanding you correctly that your thinking that I could feed both panels from the one input connection? I hadn't thought about doing that, but I like it. Less parts to buy and I don't have to plug and unplug. So what means of input connection would you think best? Something like a small 50A subpanel wired with a two 30A 240V breakers- one feeding to the breaker in each panel? Or just bi wiring the input plug to go to both panels. Not sure exactly how I would bi wire the input receptacle with two 8 or 10Ga wires for each leg. Thoughts?

You don't need the sub-panel.

Whatever you pick as the generator input connector. This would be a male on the house, that rating should determine the wire size. The interlocked breaker should be rated the same.

Your generator breaker will ultimately determine the max current of the "system" and each feed to the main panels should be rated for that value.

e.g. 50A generator connector, 50A or less generator breaker

Wire rated for 50A to panel #1
Wire rated for 50 A to panel #2

Depending on ease of wiring, this might be the easiest. Junction box inside where all three are connected using wirenuts, split bolts or specific splice blocks.

Once your on backup power, the mains are off and your free to engage or turn off either backfed breaker.

Wiring is such that the current can be split as fit to each panel or the maximum current can be sent to either.

These are example generator input connectors. 50-Amp Power Inlet Boxes @ Electric Generators Direct - Your Online 50 Amp Power Inlet Box Superstore (http://www.electricgeneratorsdirect.com/accessories/50-amp-power-inlet-boxes.php)

My only suggestion is to include a mechanism that can be added later to be able to measure the generator output from inside.

This usually consists of a couple of current transformers that go around the conductor and a connection to the voltage. They usually mount in a DIN package (92mm x 92mm) hole and some depth.

It could be pricey though, but it might be worth considering.

It might also be useful to be able to determine when power is restored. Not sure exactly how to do that. I'd have to do some research.

I would wire for 50 amps for what you describe, an inlet box as provided in KISS's link.
Don't know if code will allow the 50 Amp inlet box can go to a 50 Amp breaker in both panels, that have an interlock kit on both panels, both panels would need an Interlock kit, so only the 200 Amp Main OR the 50 Amp Generator Breaker to be on at a time.
GE Interlock kit:
Generator InterLock Kit - General Electric Kits (http://www.interlockkit.com/genelecmain01.htm)
This show an actual kit in Place:
Generator InterLock Kit (http://www.interlockkit.com/index.htm)
Even at $150.00 a piece, it is probaby one of the cheapest options.

Just curious... I was told ,although the main is off when backfeeding. The main ground should be disconnected also ,hence this is the line that would be sent back to the utility is this correct?

Main off is OK, the issue is the Main needs to have either a manual or automatic method of keeping the Main off when the panel is powered by a generator, using either an interlock kit, or manual or automatic transfer switch.