Grounding Question

Mike56
Mike56 Registered Users Posts: 2

Hi.

Re: Magnum Battery Inverter MS4448 PAE. 4400W, 48 VDC, 120/240 VAC 60Hz

We luve off grid in an usland here in Belize, C.A. We have no grud VAC or generation hooked into our system. It will run off 48V battery bank powered by solar panels.

My question is...on our inverter connections I see ground IN, ground OUT and Equipment ground. Do I need to ryn the grounds IN & OUT to my house panel? (30 feet away )

In the house I have a main Circuit Breaker Load Center (Square D, QO by Schneider Electric )

Thanks for any help, Mike

Comments

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭

    IMHO, you should run from the inverter ground OUT to the AC panel ground. With no secondary AC (grid/generator/etc) the inverter ground IN would be unused (as would AC live and neutral INs).

    Check the inverter manual, but I think there should be a neutral-ground bond made in the AC panel.

    Off-grid.  
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  • Mike56
    Mike56 Registered Users Posts: 2

    Thanks why do I bond the neutral to the ground ? Won't this make the ground carry current all the time?

  • BB.
    BB. Super Moderators, Administrators Posts: 33,402 admin

    Generally, you want to "bond" the Neutral to Green Wire/Safety ground in one location... For North American homes, that is typically inside the main breaker/fuse panel (you will see both a green wire ground bus, and a white wire neutral bus--And somehow, they will be attached together inside the panel).

    Note, this is not really true outside the home.. For example, you have a pole mount 120/240 VAC Split Phase transformer on the pole. The neutral is grounded (typically) at the base of the pole. Also, this transformer serves ~5 homes on your block, and each home has a ground to neutral bond too). In the grand scheme of things, this is very good for lightning control (lightning takes the shortest path to ground--It does not like to follow electrical wiring more than a few 10's of feet). And the resistance from ground to earth only carries, perhaps, 5-10 amps or so worst case (120 VAC / 25 Ohm worst case grounding=4.8 amps)--So, the "AC ground current" does not really do much when you have 5 volts drop from pole to house (5 volts / 25 Ohms=0.2 amps).

    Inside your home, when you have "single point" ground to neutral bonding, there is no connection for parallel current flow on both Neutral and Ground wire.

    However, if you tied white to green both in the main panel, and (for example) at an outlet. Then the current flow will be divided between white and green because of this. And we do not want this (don't want current flow through green wire unless it is, for example, a short circuit from Hot to Ground--To trip the breaker). There are further details why multi-point grounding of a home's neutral system with the safety ground is not good/safe... We can discuss more if you are interested.

    Grounding is one of the most complex questions we talk about here... There is a good reason why the best idea is to follow code--This helps reduce "inadvertent" problems (things people and equipment don't "expect").

    Things do get complicated when you talk about gensets and RV installations with multiple power sources (utility, genset, AC Inverter).

    For example, in my (limited) experience, more or less, smaller (3,000 Watts or less?) gensets and AC inverters do not ground bond neutral and ground. And most will ground bond in the genset/inverter if over ~3,000 Watt output. So, this gets complicated when you are powering your home with utility power, a backup genset, AC inverter... The typical answer for your home, is to make sure that the white/green wire bond is "lifted" in the (larger) gensets and AC inverters.

    For RVs, because of the complexity (for example, at the RV park, their neutral/green wire ground is somewhere back on their AC panels). Using a transfer switch with an extra lead to ground bond when the genset or AC inverter are supplying power, and "not bond" when utilty power is supplied.

    And even more complexity, (generally) you should only ground bond a PSW/TSW (pure/true sine wave) AC inverter (Hot and Neutral are "floating"/isolated by a transformer). For MSW (modified square/sine wave) do not neutral/ground bond the output of AC inverters because the AC output is not isolated (connects back to the battery +/- bus, no transformer isolation).

    That is some of the details behind why the answer depends on your system's details. Short answer is neutral+ground bonding does not create a parallel current path with single point bonding.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MrM1
    MrM1 Registered Users Posts: 487 ✭✭✭✭

    But if Ur ground enters earth at 2 points... Even if those 2 points are also bonded to each other, AND even if all Ur neutrals are only bonded at the main panel and there (and there only) also bonded to ground, that is bad?

    REC TwinPeak 2 285W 3S-3P 2.6kW-STC / 1.9kW-NMOT Array / MN Solar Classic 150 / 2017 Conext SW 4024 Inverter latest firmware / OB PSX-240 Autotransfomer for load balancing / Trojan L16H-AC 435Ah bank 4S connected to Inverter with 7' of 4/0 cable / 24 volt system / Grid-Assist or Backup Solar Generator System Powering 3200Whs Daily / System went Online Oct 2017 / System, Pics and Discussion
  • BB.
    BB. Super Moderators, Administrators Posts: 33,402 admin

    If I follow you correctly, sounds find.

    You can have multiple ground rods... Either (or both) for better lightning grounding or if you have sandy/dry/rocky soil that has poor conductivity. I suggest that running a 6 AWG between ground rods improves "safety grounding" for AC voltages and better lightning control.

    "Earth Grounding" for your AC power does not really make things electrically safer (120/240 VAC). Tying Neutral to grounding and 'big metal" (water pipes, gas pipes, electrical panels, etc.) is what makes things safer. This provided a return path (from "grounded metal" back to the ground+neutral bond) so that a circuit breaker can be tripped.

    Earth Grounds are generally for lightning protection (get lightning energy away from house). A short circuit from 120 VAC "Hot" only will drive ~5-10 amps into the earth--Not enough to trip a breaker.

    Other grounding issues that "need earth grounding" such as making some fluorescent tube fixtures start easier, spark ignition on stoves for flame detect, and cathodic pipe/ironwork protection ("charge" the pipes so they do not rust, phone systems so they do not have their wires corrode when they get wet)...

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭

    just a note - Gas lines/pipes are not generally allowed to be tied into the ground system. They are often tied into a cathodic protection system to prevent corrosion

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,402 admin

    In the USA... In general (I am not a code expert) there is a galvanic isolation (fancy name for "insulated pipe joint" joint out at/near the gas meter (line in ground is part of utility's cathodic protection system. In the house, the gas lines were "floating").

    Today, our local code requires that the gas line and hot water line be tied (grounded) to the cold water pipe and ground rod (add ground rod if not present in old / original structure).

    -Bill

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