Inverter/Generator Neutral Bonding

MontanaJCMontanaJC Posts: 1Registered Users
Hello, I have a small off grid cabin that I am wanting to power with a Freedom XI, a 2000 watt pure sine inverter with built in transfer switch. One issue that I have is that the inverter has an internal relay which bonds neutral to ground when inverting. When shore power (a Honda eu2000i) is detected, it lifts the bond. In summary, the cabin's main panel is bonded, the Honda is not bonded, and the inverter is bonded while on battery. The solution I think the manual is getting at is that as long as the inverter is downstream of the generator, all should be well.

The solution that I think may work is to add a small panel, a 30 amp, one breaker panel (disconnect) that has a NG bond and is grounded to the standard 2 rod system. Then from this panel, power goes to the inverter input, and out to the former "main" panel which is NOT bonded, but grounded separately (manual says that input AC neutral must be separate from output AC neutral). I think I can also ground the inverter chassis to this ground.

Could someone look over this image to see if this is a stupid idea?

Thanks in advance for your time!



  • mcgivormcgivor Posts: 2,331Solar Expert ✭✭✭✭✭
    Generally there should only be one neutral bonding point, which usually is in the AC distribution or output of the inverter, a relay which "lifts a bond ?" would imply that it is not in fact a bond, as a bond is a permanent connection between neutral and ground.. Sounds strange but anything is possible, what make and model is the inverter ? The wiring instructions that came with my inverter specifically says connect neutral to ground on the output of the inverter and as there can be only one bonding point, that would be it.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • Raj174Raj174 Posts: 648Solar Expert ✭✭✭✭

    I believe this is the correct manual for OP's inverter

    3600W PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 54.4V 207AH LiFePO4 no BMS, 4500W genset.
  • EstragonEstragon Posts: 2,959Registered Users ✭✭✭✭✭
    The inverter is designed for mobile applications which would typically have the NG bond on the shorepower side. As such, it lifts the internal bond for shorepower.

    The generator is designed to power portable loads via AC outlets, not to feed multibranch distributions. That said, I do sometimes use an eu2000i to backfeed my cabin circuits and charge batteries. I think your plan should work (but probably wouldn't meet code, if that's an issue).
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mcgivormcgivor Posts: 2,331Solar Expert ✭✭✭✭✭
    Thanks @Raj174 didn't see the tree for the forest  :D 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • mcgivormcgivor Posts: 2,331Solar Expert ✭✭✭✭✭
    Below is an excerpt from the manual 

    AC Output Neutral Bonding
    The neutral conductor of the Freedom X’s AC output circuit (that is, 
    AC Output Neutral) is automatically connected to the safety ground 
    during inverter operation. When AC utility power is present this 
    connection is not present, so that the utility neutral (that is, AC 
    Input Neutral) is only connected to utility ground at your source. 
    This conforms to the National Electrical Code (NEC), which 
    requires that separately derived AC sources (such as inverters and 
    generators) have their neutral conductors tied to ground in the same 
    way that the neutral conductor from the utility is tied to ground in 
    only one place. Check the regulations for your specific application 
    to ensure that the installation will comply with the necessary 
    requirements. In other words, the AC Input Neutral and Output 
    Neutral must be isolated from each other.

    My interpretation is that if there is a transfer to utility power, the inverter will not establish a neutral bond because there is already one established at the utility. Being that this is not an inverter charger, the sole purpose of connecting an outside source would be to pass through power to the loads, which would require the inverter to be on and inverting. Using a generator as an AC source without neutral bonding would mean the inverter would establish a neutral bond thereby conforming to the rule of a single neutral bond point. So in essence bonding the neutral of the generator, before the input to the inverter, would prevent the inverter from establishing a neutral bond, thereby being redundant. This inverter, it seems, is designed primarily for marine or RV use which uses an engine driven alternator as a charging source, but could be connected via a charge controller to source. Any other interpretations on this?
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

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