hoping someone could check my schematic (growatt 5k es, auto transformer, load centers)


New Member
Dec 19, 2021
Nevada, western mountains
Hello all, first time poster long time lurker. I have some experience with small solar systems but this is my first time building something larger and bigger. It's going to run a ranch style property (all offgrid). I'm trying to wrap my head around the legs/phases wiring that I've seen you YouTube. I'd like to have a 240 panel and a separate 120 panel. My plan was to do them like this and again, hoping someone can point out how it doesn't work and what to fix.

I haven't included ground in any of this because I haven't read far enough into that yet (particularly if the inverter is tying neutral and ground together. I'm also not including the batteries, solar input, or aux ac input as I feel I have a good handle on those.

Some of my questions are, if the whole thing isn't crap to start with:

  • Can I treat the 240 sub panel the way that I am, just using single pole breakers, no master breaker? I would have L1 enter on phase 1 bus bar and L2 on the panel's neutral. That would let me (I think) use other single pole breakers on phase 1 bus bar for 240 loads.
  • Am I doing the 120 sub panel the right way? I think this would let me just treat it like a regular 120 panel since the autotransformer will keep neutral at 120. I should be able to put single pole breakers on bus bar 1 and 2, put the load's neutral on the neutral bar, and bob's my uncle, right?
  • Not in the diagram, and maybe this is too busy already, but I'd like to make sure that *only* 110-130 is hanging around on that 120 panel, so I was planning on researching a way to make sure that if the voltage gets off I can trip something early.
Thanks in advance for any help.



Photon Sorcerer
Oct 15, 2020
In my opinion, perhaps also based on some electric code(?, which I am not an expert at staying on top of), L1 and L2 of the Growatt should only be feeding the L1 and L2 busses in the 240v panel (you don't want a single pole breaker on any of your 240v loads. But also, you don't know if L2 is grounded or floating (inside inverter), I wouldn't even want it close to the neutral bus bar in the box.

What I would rather do (check your local code requirements and the NEC code), is wire the L1 and L2 from Growatt, into the 240v panel to the normal L1 and L2 busses, for your dedicated 240v loads, and also install an appropriate sized double-pole breaker in that panel which would feed the auto-transformer primary coil, then have L1, L2, Neutral, from the auto-transformer secondary side (the outputs), go to feed your 240v / 120v breaker panel, and if you only desire to use that for 120v loads, then just populate it with only the single-pole breakers (keeping all your double-pole breakers in the 240v-only box)...

Then you would be dedicating the auto-transformer for 120v loads only, helping to free up its capacity by keeping the dedicated 240v loads off of it, pulling those directly off the Growatt (assuming that was what you are attempting to achieve by not running all the 240v loads also off the transformer)...

Of course you would have to check this all out with your codes and make sure I'm not full of it here either hehe...
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