Inverter Neutral tie

JBonfireJBonfire Posts: 5Registered Users ✭✭
I have a sub panel for my inverter (AIMS 6KW)

Can I tie the out neutral from my inverter to the main panel neutral?

Comments

  • BB.BB. Posts: 27,777Super Moderators admin
    You have to be very careful on this... In General, PSW/TSW inverters are (sort of) OK to tie to the main panel neutral.

    And in general, MSW inverters are likely to cause shocks and possibly go up in smoke (depending on AC and DC wiring) if you connect any of their AC outputs to a common/shared neutral and/or ground bonded neutral.

    Check the manual for your inverter to see what type you have and what grounding is required/supported/suggested. On many "simple" inverters, their grounding and interconnect discussions are very thin to non-existent.

    Generally, you should be using transfer switch(es) which switch out the Hot(s)+Neutrals from AC mains to AC genset/AC inverter.

    Are you "in love" with the AIMS AC inverter?

    Getting an AC inverter that both AC mains in (some have Aux genset input too), and AC protected out--These devices have the internal transfer switches needed are designed for a safe installation for complex emergency/shared power systems (and are UL/NRTL Listed for the application). Of course, these do cost more than the less expensive "simple" import AC inverters.

    If you are trying to have an integrated (few/some/all) of your homes AC Branch circuits to have the option of AC Mains vs AC inverter+battery backup power... Be very careful. Most building departments will look very closely at backup power systems that are tied to your main panel. And many utilities are quite picky too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Posts: 2,164Solar Expert ✭✭✭✭✭
    edited July 10 #3
    For reasons of incompatibility it is difficult to give a definitive answer, some inverters state very clearly there  should be no neutral bonding, whilst on the other hand quality units insist on doing so, this is probably why there is a reluctantly to answer your query directly.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • JBonfireJBonfire Posts: 5Registered Users ✭✭
    edited July 10 #4
    That's why im confused. A friend electrician said it was always ok.
    User manual talks about never tying the IN ground with the OUT neutral but it doesn't say anything about the out neutral with the main power company neutral.
  • BB.BB. Posts: 27,777Super Moderators admin
    The typical PSW/TSW (pure/true sinewave) inverter has an isolated AC output... Basically a transformer between the DC battery bus and the AC output (hot/neutral/etc.)

    Typical MSW (modified sine/square wave) inverters typically do not have an isolated AC output. Basically, there is an electrical connection between the AC output connections and the DC battery bus input connections.

    If there is any connection between DC battery and AC output. Typically, DC battery bus is "grounded", and standard North American AC split phase 120/240 VAC power has the "neutral" white wire bonded/connected to local ground too. This DC to AC ground/neutral bonding will short out the MSW inverter.

    And typically, larger gensets and AC TSW inverters (typically over ~3,000 watts or so--I guess) have the the neutral wire bonded to the genset frame ground or inverter case ground.

    This default ground connection is "in potential conflict" with the neutral to earth bonding typically in the main breaker panel of the home. Ideally, you only want one ground to neutral bond in your system.

    If you bond the neural+earth bond in two locations, you now have a parallel current path between the genset/inverter and the main AC panel. This allows "neutral" current to flow both in the Neutral wire and the Green wire (parallel current paths). This can cause overheated wiring/connections. And if you have (for example) a GFI outlet on the genset/inverter and plug/wire to your main panel, this will generally cause GFI (ground fault interrupters) to trip (parallel ground/neutral current path).

    That is a really quick explanation of the basic issues.... Questions or clarifications?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Posts: 2,760Registered Users ✭✭✭✭
    "Always"? I don't think so. Does the electrician friend do a lot of work on solar inverter systems? Most don't, and may never run across situations where not everything gets tied into the house wiring the same way.

    The neutral is likely bonded at the service panel. Assuming the "in" ground is the same as the service panel ground, isn't that effectively connecting the "in" ground to the "out" neutral (which the manual says never to do)?
    Off-grid.  
    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
  • JBonfireJBonfire Posts: 5Registered Users ✭✭
    " Does the electrician friend do a lot of work on solar inverter systems? "
    -No, and that's what worries me.

    "The neutral is likely bonded at the service panel."
    - Yes the neutral is bonded to the ground at the panel. my original idea was to run a dedicated ground rod for the inverter that will be >10feet away from the main panel ground rod. Would that be ok?

    "Assuming the "in" ground is the same as the service panel ground, isn't that effectively connecting the "in" ground to the "out" neutral (which the manual says never to do)?"
    I was more nervous about being the neutral from the power company since my transfer switch only transfers the loads not the neutral
  • JBonfireJBonfire Posts: 5Registered Users ✭✭
    > @BB. said:
    > You have to be very careful on this... In General, PSW/TSW inverters are (sort of) OK to tie to the main panel neutral.
    >

    Mine is PSW

    >
    > On many "simple" inverters, their grounding and interconnect discussions are very thin to non-existent.
    This is my case.



    >
    > Generally, you should be using transfer switch(es) which switch out the Hot(s)+Neutrals from AC mains to AC genset/AC inverter.
    I bought a trans2 couple of months ago now im stuck

    > Are you "in love" with the AIMS AC inverter?
    U are making me a little nervous here... Not in love "in love" with it its still in the box but can't return it. What do you have in mind?

    > If you are trying to have an integrated (few/some/all) of your homes AC Branch circuits to have the option of AC Mains vs AC inverter+battery backup power...
    That's exactly what im trying to do.

    > Be very careful. Most building departments will look very closely at backup power systems that are tied to your main panel. And many utilities are quite picky too.

    Your help is greatly appreciated. I will be extra cautious.
  • EstragonEstragon Posts: 2,760Registered Users ✭✭✭✭
    > @JBonfire said:
    >
    > "The neutral is likely bonded at the service panel."
    > - Yes the neutral is bonded to the ground at the panel. my original idea was to run a dedicated ground rod for the inverter that will be >10feet away from the main panel ground rod. Would that be ok?

    I'm not generally a fan of having multiple ground points because "ground" potential is quite local. In a thunderstorm, for example, you could end up with separate grounds assumed to be at nearly the same potential voltage, but briefly at high voltage with respect to each other.
    Off-grid.  
    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: 2,164Solar Expert ✭✭✭✭✭
    Being  TSW/PSW is not always an indication of wether a neutral can be established, case in point, I have a cheap "Pure Sine wave" inverter, for backup, which states in the literature, do not ground one leg to establish a neutral, without rationale. My assumption would be that such inverters are not intended to be integrated into a grid supplied system but rather as a stand alone floating neutral, which is in fact not a neutral at all. My particular example, according to the manual, uses ground fault to provide safety, but nowhere is there a provision to establish a ground, as in a ground lug,  the manual has no mention of how or where to do so, which is puzzling, without an established ground how could it determine a fault? Higher quality units have provision for neutral bonding, as well a comprehensive 100 page manual as opposed to a 10 page installation guide, if in the manual it states do not ground one leg, would probably mean it will fail if done. Just some thoughts.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • BB.BB. Posts: 27,777Super Moderators admin
    Ground rods--They really only are useful for lightning and static discharge control. It does not really do much for day to day 120/240 VAC 60 Hz system operation (~25 Ohms maximum from ground rod to earth).

    Ideally, you want all "grounds" (rods, cold water pipes, ground plates, etc.) to be tied together with minimum 6 AWG wire (smaller diameter gauge is more likely be vaporized with a direct lightning strike).

    Tieing the grounds together with 6 AWG cable is useful to "short circuit" any short circuits from Hot wires to "grounded" metal objects (plumbing, metal sinks, water heaters, gas heaters, metal electrical conduit/boxes/panels, etc.).

    If you did not have a "solid" ground connection between the various system grounds (cold water pipes, multiple ground rods), you can accidentally energize a local ground rod... This has been known to electrocute larger animals (cow, one leg close to ground rod, other father away, current through heart). Or you could end up with an "energized metal structure" (for example, 120 VAC tool/outlet energizing your solar panel framework--Creating a shock hazard to people.

    If you want/need to discuss grounding more, I will lookup some more links for you. Grounding is not a simple subject. Here is one post...

    -Bill
    BB. said:
    Re: Working Thread for Solar Beginner Post/FAQ

    A couple threads about Lightning:

    Off Grid Grounding Technique?
    Another Question, this time about Lightning

    Note, the above are discussions, not a do A, B, and C--and you will be "safe". There probably is no such thing with lightning. Several different techniques are discussed--and a few of those posters even have experience with lightning. :cool:

    And our host's FAQ:

    Lightning Protection for PV Systems

    From other past posts here, Windsun (admin/owner of NAWS), he said that most of lighting induced failures he saw were in the Inverters' AC output section.

    Towards the end of this thread is a very nice discussion of proper generator grounding.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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