MSW inverter Voltage between Neutral and ground

deltarat
deltarat Registered Users Posts: 9
We have a Magnum MM1524AE Modified Sign Wave inverter tied into a sub-panel of a off-grid cabin. There is ~30vac
between neutral and ground. Is this normal?

Comments

  • thenderson4
    thenderson4 Registered Users Posts: 16 ✭✭
    Re: MSW inverter Voltage between Neutral and ground

    If you observe the way way most power companies do it, they will "Bond" the Neutral to Ground. If your system is isolated, (floating) then how can it know that you want the Neutral to be at "Earth" potemtial?

    As is said by others on this forum, it is always best to check with the company which made your inverter to see what they say. (about Bonding the Neutral to Earth Ground) (which means connecting)
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: MSW inverter Voltage between Neutral and ground

    CAUTION! CAUTION! CAUTION!!!!!!!!!!
    In almost ALL cases, if you bond the "neutral" of an MSW inverter to ground, INSTANTLY, magic smoke will come out of the inverter, it may make several interesting popping, snapping sounds, and it will become quite dead! :cry: After all the damage has been done, it's fuse will then blow.
    There is no traditional neutral on MSW inverters, the output lines are "floating" above and below negative ground, so grounding either output line will place a short circuit on one side of the inverter output and destroy it. If the panel your inverter is to feed has it's neutral grounded, that bond must be opened up/removed. Then be aware that you can get a jolt from either line if you're standing in water without your boots on. But at least your inverter will live to see another day :D
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: MSW inverter Voltage between Neutral and ground

    The Magnum MM1524AE allows grounding of neutral. Neutral should be connected to ground at the main breaker box. This ground should go out to a grounding rod. The 30 vac you are now reading will go away as soon as neutral is connected to ground. It is just RF interference capacitors from each AC output pin to ground prong that is giving the reading with a floating neutral.

    See figure 6 on page 7 of op's manual. At main breaker box neutral will be bonded to ground (which is also connected to main breaker box case). Green wire going to inverter should be connected to main breaker box case. The aux box should have green wire coming from inverter also connected to its case. Neutral bus bar in aux breaker box should NOT be bonded to is case. Neutral will gets its ground bonding back at the main breaker box.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: MSW inverter Voltage between Neutral and ground
    RCinFLA wrote: »
    The Magnum MM1524AE allows grounding of neutral.
    Thanks for that RC, good to know that at least one MSW exists that will allow this.
  • SolaRevolution
    SolaRevolution Solar Expert Posts: 410 ✭✭
    Re: MSW inverter Voltage between Neutral and ground

    A possible "Why" your system was installed without an AC Neutral bond.

    The National Electrical Code (NEC) requires the AC source to have a Neutral to ground bond and that there be only one such bond in the entire AC system.

    The Magnum "AE" inverters are designed for use in a structure.(hardwired installation) It has a solid connection between the AC input Neutral and the AC output Neutral.

    In many small "cabin" systems with fairly small inverter/chargers there is often a small portable generator used to charge the batteries when other charging sources are not available or inadequate for meeting the load demands. It is common for small portable generators to have only GFCI (Ground Fault Circuit Interrupter) protected AC outlets. The problem is that if your cabin's AC system has a neutral to ground bond it will cause the GFCI protection in the generator to trip and you will not get any power from the generator.

    To do it "the right way" you would need to get a generator with a non-GFCI outlet. Unfortunately for small system owners this is usually only available on the higher amperage (30+ amp) outlets. The "get-er-done" meathod is to remove the cabin AC panel Neutral to ground bond. There is a good chance that this is what has happened in your case.

    The non-AE Magnum inverters are designed for mobile applications and have built in neutral to bond relays which can disconnect the internal neutral to ground bond so only the (removable) AC source has a Neutral bond connection when you plug into shore power or a portable generator so there is no problem with the GFCI protected circuits.