Breaker size and general electrical layout

[Beachfinn]

Good Afternoon,
after consulting the search function and the friendly google, I still find myself not so clear about few details, so might as well ask the gurus 

I have attached a pretty picture that may make the question understandable, or complicate things tremendously.

I think I have most of the system figured out; the magnum pre fab enclosure takes the guesswork out of the inverter end and is pre wired for solar. I still need a mega breaker on the battery bank negative, that I am not quite sure of sizing (I believe it's 200A DC). it's 8x 6v golf cart cheapy batteries, wired series/parallel to produce 12v, so around 800A of storage. all that DC wiring is 4/0 all the way to inverter, as specified by Magnum. Rest of the wiring should follow the gauge recommendations for 120v / breaker, not rocket science.

Here's the main question the boggles me: 10kw generator puts out 83A @ 120v when its a beautiful day. That runs to a sub panel with an 80A main breaker. From there it goes to 100A automatic transfer switch. Other side of the switch is 30A/50A shore power. Output of that switch goes to the main 120v panel. now, how is the main breaker of that panel sized? or is there a better way of doing this?

Also any corrections or suggestions to the attached diagram would be most welcome 

Link to the magnum enclosure, for those that are interested :http://www.wholesalesolar.com/2917530/magnum-energy/disconnects/magnum-energy-mmp175-30d

[Iceni John]

I have a broadly-similar system to yours:  each row of four PV panels feeds its own charge controller that charges a bank of four golfcart batteries in series/parallel, and each bank of batteries has a 250A Schottky diode for its positive output and a 300A Class T catastrophe fuse on the negative (as per Sean Walsh, who knows way more about such matters than me!).   I will also fuse each series pair of batteries with a Blue Sea terminal fuse, and the inverter has its own 250A ANL fuse.   All cabling is 4/0 and all lugs are tin-plated and crimped on with a good circumferential FTZ crimper to make a solid gas-tight connection.   Sean's idea for having a Class T catastrophe fuse is that it will blow quicker than a breaker may trip, important if hundreds of amps are flowing where they shouldn't.   Essentially I want every source of power to have a fuse or breaker, however low-current it may be  -  even the little indicator lights for reminding me I have the house batteries connected to the start batteries or the Schottky diodes are bypassed each have their own 2A inline fuses!   When dealing with potentially-lethal DC currents you can never be too careful.

John     

[Beachfinn]

Yes, i don't think there can be too many fuses and breakers
How many panels you have on the roof? I just have 4x100W that I will likely increase as I see how much space i have left.

I guess I could put a 50A breaker on the shore line, and run wire from main to that, so it can handle 80A. Then use an 80A on the main panel...

[bevans6]

People sometimes confuse the purpose of breakers.  Breakers are there to protect the wiring that is connected to them, that is all.  The capacity of the source of the electricity - in this case your generator - is irrelevant.  The only thing that matters is what size cable you use to carry the electricity after it leaves the breaker.  For 80 amps you need to use 2AWG cable.  In your distribution box, if you have run 2AWG cable between the generator box and the distribution panel you can use a second 80 amp breaker on the main input.  It's redundant to use two breakers in this manner but it makes things easy to build and it doesn't hurt anything.  Inside your distribution panel you use breakers of appropriate size to protect your branch wiring, 15 amps for 14 gauge, 20 amps for 12 gauge, 30 amps for 10 gauge, etc.

It seems odd to have a breaker at the end of a run of wire instead of at the beginning, but it will protect against simple over-current just fine.  What it won't protect against is a short on the cable run leading up to it, which is why practice says to have the breaker at the beginning of the run, not the end of the run.  In this case you will have a breaker at both ends, no harm, no foul.  It's the same as having a main breaker in a remote panel in a building, if nothing else it acts as a switch to turn off power in the panel locally if you need to work on it.

Brian