Whole house grounding using inverter

msgieser
msgieser Registered Users Posts: 24 ✭✭
in Off Grid Solar & Battery Systems #1
When I have my home electrical outlets properly wired, and they are being fed by my inverter, do I truly have a grounded system. Yes, the inverter is grounded with a bare ground wire to earth ground. I seem to be having a problem with a new high efficiency LP gas water heater. It is a power direct vent and requires a ground, but it seems that it's processor controls can not detect one.
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  • Aguarancher
    Aguarancher Solar Expert Posts: 315 ✭✭✭
    #2
    Re: Whole house grounding using inverter

    "electrical outlets properly wired"
    If you are feeding the power from your inverter through your electrical panel and it (the panel) is properly tied to a ground rod, your water heater should see the ground.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: Whole house grounding using inverter

    More questions than answers at the moment:

    What Xantrex 1,800 Watt inverter? MSW/TSW? Model Number?
    Assume we are talking about "off grid"?

    Grounding the case of the AC inverter is just for short circuit/safety concerns (if a battery or power cable shorts against the case, a fuse/breaker will be popped).

    Most TSW inverters have floating AC outputs (basically a transformer isolated output). Some smaller AC inverters may have the AC Neutral (white wire) tide to the AC inverter case (Cotek/Samlex seem to do this often).

    Most MSW Inverters do not have isolated outputs. Their AC output is "connected" to the DC battery bank, so technically they can be ground referenced through a grounded battery battery bank, but both AC leads are hot and not "neutral" as commonly defined by AC power systems.

    Also, for MSW inverters, their "Peak" AC voltage (modified square waves) is lower than the typical peak TSW (true sine wave) peak voltage--So some devices may not function as well on MSW power.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • msgieser
    msgieser Registered Users Posts: 24 ✭✭
    #4
    Re: Whole house grounding using inverter

    I just purchased a new inverter, a Sunforce Pro Series 2500 watt pure sine wave that replaced my 12 year old Xantrex that blew a power board. It is "hard wired" directly to the power feed cables going to my main house. It does have a ground connection on the back that says "case ground" What should be done to get the ground terminal on the direct wire connected to a good earth ground?....if the "case ground" isn't doing it? I do have a ground rod installed that this case ground is connected to now. Also connected to this ground rod is the grounding point for my Midnight combiner box from my solar panels. Thanks...I really appreciate the help I receive on this site!!!!
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  • msgieser
    msgieser Registered Users Posts: 24 ✭✭
    #5
    Re: Whole house grounding using inverter

    And yes...completely off grid!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: Whole house grounding using inverter

    The single main Ground Rod (usually near your main panel in tradition utility powered system) is your central "safety ground" for all... In general:

    The battery bank "-" should be tied to your ground rod.

    All electrical conduit/boxes/etc. should be tied to the ground rod (usually through the AC ground bus in the main panel).

    All plumbing (cold and hot water pipes) should be tied to ground rod.

    For the AC inverter, you will need to review their lititure. Many TSW inverters have a floating output, and you would just tie the "white wire" to the common neutral/ground bus bar(s) in the main AC panel.

    However, some TSW inverters do tie the green wire to white wire inside the inverter itself. It will be up to you if you "bond" the Neutral to Earth ground inside the inverter or inside the AC main panel.

    Generally, what you are trying to avoid is connecting the White+Green wire grounds together in two places. In some cases, you can have high current flow through one of the wires with multiple connected ground wires (parallel current paths--It is possible for high current DC power to "get into" the AC ground/neutral wires--which are much smaller, and smoke them).

    Nothing magical--It just depends on the system design. An example of a grounding "problem" would be grounding the Battery bank negative terminal, green+white inside the inverter, and again green+white in the main panel. That could get the "heavy" DC current into your AC wiring.

    If you are in a natural lighting area--you may also wish to install Midnite Surge Supressors on the Solar array combiner box, PV Entrance to the home, and on the AC main panel.

    http://www.solar-electric.com/installation-parts-and-equipment/midnite/cipr1/suprde.html

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #7
    Re: Whole house grounding using inverter

    Sounds like you need an electrician to me. Even people who are knowledgeble enough to do their own wiring, if they are smart, get a final sign off from an electrician. Its what gives you a good nights sleep.

    First of all you need an inverter that is UL listed for hard wiring into your home. Then you need to check the existing ground stake, the GEC, EGCs etc, and the earth neutral bond in the load center. The inverter and other system component cases should also be tied to the ground bus, avoiding daisy chains or joins.

    Kinda big subject, suggested reading:

    http://en.wikipedia.org/wiki/Earthing_system
    http://www.homepower.com/articles/solar-electricity/design-installation/get-grounded
    http://www.homepower.com/articles/solar-electricity/design-installation/more-system-grounding
    http://www.homepower.com/articles/solar-electricity/design-installation/grounding-and-bonding-pv-systems
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • msgieser
    msgieser Registered Users Posts: 24 ✭✭
    #8
    Re: Whole house grounding using inverter

    BB...So I should tie my DC negs. from the battery bank to my ground rod? Pick a point on the neg side and run a #8 copper wire to the ground rod? Once that is done, might the inverter see this tie in on the dc side and might the ac side complete this path internally within the inverter?
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  • msgieser
    msgieser Registered Users Posts: 24 ✭✭
    #9
    Re: Whole house grounding using inverter

    Also, green and whites are not tied in the main panel. each of the green, white, and black run back to the inverter.
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