Putting modified sine inverters through breaker panel

powerinthewoodspowerinthewoods Registered Users Posts: 5 ✭✭
I have 2 2000 watt modified sine inverters that I want to put on my breaker panel. I have a transfer switch to select generator or battery bank. I’m planning on 1 inverter on each phase of the main panel. (No 220v) The problem is the bonded neutral. My inverters can’t Handel that. How do I proceed?


  • wellbuiltwellbuilt Solar Expert Posts: 636 ✭✭✭✭
    Hmmmm , there is a little green screw in the panel that grounds it . Remove the screw . 
     Then check for ground . 
     It’s kinda risky working with no ground and it won’t pass inspection ☹️
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    edited April 18 #3
    What Wellbuilt is referring too (in detail)--MSW inverters usually do not have "transformer isolation" between the DC input and the AC output...

    Normally we tie the DC battery bank negative to earth/safety/green wire--That is for safety (i.e., if a + VDC lead shorts to metal sink/plumbing/electrical box, the current finds it way to safety ground then to negative battery bank terminal--This pops the DC + Fuse or Breaker).

    And in North America, we do the same thing for AC utility power... The "Neutral Wire" (white wire/neutral bus) is tied to the same ground rod earth ground/cold water pipe/electrical box grounds.

    With MSW inverters, if you tie the DC negative (or positive) ground terminal to the AC white/neutral terminal, you will short circuit the MSW inverter and less the magic smoke out of the inverter.

    If you do not "ground reference" the battery bank (let it float)--You will not have a short with the grounded neutral. And now the "battery bus" is "Hot" with respect to ground.

    OR, you ground reference the battery bank (i.e., negative ground), and float the L1 and L2 output of the MSW inverter--That will work...

    HOWEVER, again in North America, for safety we ground reference the 120/240 VAC neutral bus to safety ground--And as Wellbuilt says, no ground bonded neutral makes your house wiring non-compliant with code, and "unsafe" for NEC compliant wiring.

    You can do "anything"--But the NEC (national electric code) is designed around the whole requirement that the white wire/neutral is ground referenced. This allows you to only install 1 pole circuit breakers for 120 VAC circuits (just on the black or red wires--White, no breaker)...

    For "floating" outputs, you need to have 2 pole breakers--One on the Black/Red and a second on the White wire--Which no North American home has (you need a third "neutral bus" with breakers).

    Your only safe (and possibly code compliant) installation option is to install a mixed utility power/backup inverter power system is to use a TSW/PSW (true/pure sine wave) inverter (which almost always have transformer isolated outputs). And a properly designed/installed DC/AC/Transfer Switch system (true transfer switch or AC interlocks on main/sub panel).

    MSW inverters are really only for stand alone power, or if you use a sub panel with a 2 pole (at least) transfer switch that disconnects both Hot and Neutral from AC mains, and connects to L1 & L2 MSW AC output... If your MSW inverter is >1,800 Watt output @ 120 VAC--Then you should use a (120/)240 VAC panel with 2 pole ganged breakers (one bus to L1 and the second to L2)--You will only get 120 VAC (not 240 VAC), but it will be much safer (both L1 & L2 wires from MSW inverter have breakers).

    The problem with doing things "different"--Is the next person to work on the system (electrician, other than you)--They will be pretty confused about what you did and how to repair/upgrade.

    I don't see any safe way you can wire this MSW inverter to your main panel safely/to code.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wellbuiltwellbuilt Solar Expert Posts: 636 ✭✭✭✭
    ^^^^^^^^^^^^^^^ this 
     thanks bill great explanation 
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • powerinthewoodspowerinthewoods Registered Users Posts: 5 ✭✭
    Hi everyone. The easiest way would be for me to purchase different inverters. If I had 2 true sine inverters the bonded neutral issue would be solved?
  • mike95490mike95490 Solar Expert Posts: 9,274 ✭✭✭✭✭
    The 2 inverters  need to be of a style that will sync with each other unless there is ZERO chance of any 240V appliances.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • powerinthewoodspowerinthewoods Registered Users Posts: 5 ✭✭
    There is no 220 volt in the cabin. 1 inverter for phase A and 1 for phase B. Gives me 4000 watts running over the 8 circuits of the panel. 
  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    edited April 20 #8
    Backing up a moment...

    You have 8x circuits and only need 120 VAC.

    How much Wattage do your need? Both running Watts and starting surge (i.e., a typical compressor 120 VAC fridge/freezer takes about 5-6 amps to Start, 4-5 amps to defrost (if "frost free"), and around 1.0 amps running compressor).

    Typically, for a cabin with AC inverter fridge, LED lights, cell phone charger, 12 volt (or 24 volt) RV Water pump, etc. needs a minimum of ~1,200 to 1,500 Watt 120 VAC inverter. And a battery bank (say 24 volts and 3,300 WH per day--a very efficient home/cabin with energy star rated fridge/freezer, LED lights, small laptop computer, RV style DC water pump):
    • 3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max planned discharge * 1/24 VDC battery = 647 AH nominal battery bank
    For charging a typical battery bank, 5% rate of charge minimum (weekend/sunny weather cabin), to 10%-13% solar charging for full time off grid (for happy battery bank). Upwards of 20-25% rate of charge if needed and/or for an AC Genset battery charger:
    • 647 AH * 2 9.0 volt battery bank * 1/0.77 solar panel+controller deratings * 0.05 rate of charge = 1,639 Watt array minimum
    • 647 AH * 2 9.0 volt battery bank * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 3,277 Watt array nominal
    • 647 AH * 2 9.0 volt battery bank * 1/0.77 solar panel+controller deratings * 0.13 rate of charge = 4,620 Watt array "typical" maximum
    Also need to calculate the size of the array based on your daily loads and location... Dartmouth Nova Scocia, fixed array facing south:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 45° angle from vertical:
    (For best year-round performance)


    Say you will be using the system (using solar) for 9 months of the year, and shut down and/or using genset in winter:
    • 3,300 WH per day * 1/0.52 off grid AC system eff * 1/3.71 hours of sun per day (February break even) = 1,710 Watt array (Feb break even)
    So, we are looking at a range for a 9 month full time cabin of ~1,710-3,277-4,620 Watt array... (more panels, less genset runtime, more "free" daytime energy for other loads--Cooking, coffee, water pumping, washing machine, etc.).

    And about your panel--Not connected to any utility power--You could simply connect the A and B buses in the present breaker panel to L1 (Hot) from your inverter/genset, and connect the Neutral bus (grounded if TSW/PSW) to White on your inverter/generator (assuming sine wave inverter).

    MSW inverters are "cheaper" than typical PSW/TSW inverters... And for some loads even more efficient... However, refrigerator compressors, some battery chargers (and tool chargers), and some electronic power supplies "do not like" MSW wave from (modified square/sine wave). They can overheat and/or make a 120 HZ bus.

    You don't want to exceed the current rating of your circuit breaker panel (say it is rated at 120/240 VAC 80 amps)--You would not want to exceed 80 Amps @ 120 VAC (p=v*i= 120 VAC * 80 amps = ) 9,600 Watts @ 120 VAC -- Which is way more than you are planning (4,000 Watts for you plan, vs 1,500 Watts for "my" plan).

    Not saying the above is written in stone or that my guesses are "right" and yours are "wrong"... Just putting some sticks in the sand for basic system / back of the envelope design--Which is much cheaper to do on paper than to start buying hardware.

    In general, it is almost always cheaper to conserve energy (most efficient, use as little electricity as practical for your lifestyle) than to have a larger system to generate "more power".

    Your thoughts?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wellbuiltwellbuilt Solar Expert Posts: 636 ✭✭✭✭
    I have a full panel here the main breaker it just a on off switch  
     With 30 breaker ? 
      The cabin is wire like a on grid home 
     I use no 240 volt 
     both legs of my panel are just power with a jumper from pole A to pole B 
     I Use one inverter out back3600 watt 48volt system . The system just works . 
      The inverter charges the battery’s allso 
     I see no advantage in running 2 inverters . 
      My system has one ground point @ the inverter . 
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • powerinthewoodspowerinthewoods Registered Users Posts: 5 ✭✭
    Wow, you guys take this stuff very seriously . I’m more of building and learning as I go. If the solar array I put together isn’t enough(1500watt with 500ah storage) I’ll fix it as I learn. I have to start somewhere without breaking the bank. Thanks guys for all the comments and please keep them coming! The cabin is mostly weekends 12 months a year. Also thinking of wind in the near future. What are your thoughts on that?
  • mcgivormcgivor Solar Expert Posts: 3,815 ✭✭✭✭✭✭
    Many here have learned through experience, much like what you are doing now, learning as you go,  in many ways that is the best, but heeding advice will save money in the long term.

    Overestimating the availability of energy stored in batteries is the most common mistake followed closely by undestimating the requirements needed to return the withdrawals plus interest as solar modules do not produce their rated output and batteries along with the electronics needed are not 100% efficient.

    Wind in most cases is not worth the effort or expense, invest in solar as panels are currently extremely inexpensive, unless your trees look like this, in which case wind may be a viable option.

    Remember these two things, shortcuts will slow you down and don't go broke saving money. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • powerinthewoodspowerinthewoods Registered Users Posts: 5 ✭✭
    edited April 20 #12
    Well said. My lot is 15 acres with a grade to the River. The high point of the property has a fair amount of gentle breeze to 20kph wind. There is a 6 acre lawn on the south side of the cabin that the sun wraps around as the day goes by. That side of the roof is 350 sqft. Plenty of space for a larger array if needed. Maybe I’ll stay out of the wind until I learn more!
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