Multiple Inverter Hookup

andy300zandy300z Posts: 39Solar Expert
Hello Guys,
I am in the process of hooking up (2 ) 12v inverters. I using one for a sump pump (shed) and i using the other pure sinewave for my (office).
I want to wire the ac output to a 2 circuit ac panel so i can have a breaker to each location.
I know that the hot wire (black) will be on each breaker is it ok to combined the neutral wires (white) on the one neutral bar in the panel ? Please keep in mind that one inverter is modified sine wave and the other is a pure sine wave. Thanks.

Comments

  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭✭
    Re: Multiple Inverter Hookup

    First, make sure both inverters have groundable neutrals.

    You can put one as L1 side of breaker box and other as L2 side of breaker box.
  • andy300zandy300z Posts: 39Solar Expert
    Re: Multiple Inverter Hookup

    I am using the morningstar 300 pure sine and a powerbright modified they both say on the intructions that they must be earth grounded.
  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Multiple Inverter Hookup

    Please note that a lot of MSW inverters do not play well with grounded neutrals, in fact they go up in smoke. The Suresine does fine with a grounded neutral.

    T
  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭✭
    Re: Multiple Inverter Hookup
    andy300z wrote: »
    I am using the morningstar 300 pure sine and a powerbright modified they both say on the intructions that they must be earth grounded.

    Not the same thing.

    Case of inverter grounded is not neutral grounded.

    The wider blade of the two flat plug prongs is neutral (white wire). Looking at 3 wire grounding plug with round ground prong below, neutral is wider prong on left side.

    Many inexpensive MSW inverter are H-bridge output with neutral side floating. They need to have an optical isolated feedback loop to DC-DC boost circuit to allow grounding neutral of H-bridge output.

    Morningstar Sure Sine is okay to neutral ground. See fig. 6 in operator manual.

    Powerbright manual for low power units says nothing about groundable neutral. I usually assume inverter that have only regular output AC sockets as NOT groundable neutral. You can always try a short wire from neutral side of plug to battery neg line to see if it blows its fuse (or inverter).
  • andy300zandy300z Posts: 39Solar Expert
    Re: Multiple Inverter Hookup
    RCinFLA wrote: »
    Not the same thing.

    Case of inverter grounded is not neutral grounded.

    The wider blade of the two flat plug prongs is neutral (white wire). Looking at 3 wire grounding plug with round ground prong below, neutral is wider prong on left side.

    Many inexpensive MSW inverter are H-bridge output with neutral side floating. They need to have an optical isolated feedback loop to DC-DC boost circuit to allow grounding neutral of H-bridge output.

    Morningstar Sure Sine is okay to neutral ground. See fig. 6 in operator manual.

    Powerbright manual for low power units says nothing about groundable neutral. I usually assume inverter that have only regular output AC sockets as NOT groundable neutral. You can always try a short wire from neutral side of plug to battery neg line to see if it blows its fuse (or inverter).

    Thanks for the detail info. This is what i want to achieve. I have a submersable sump pump which consumes about 960watts. I have a power bright 2300/4500 modified sinewave inverter,when i plug my ground detector into the inverter receptacle it shows an open ground on the reading.I also have the inverter grounded to earth.

    I will like to know if i can use this for my sump pump and is this safe to do since the ground shows open on my ground detector can this lead to a shock hazzard since the pump is completely submerged in water.

    Thanks
  • mike95490mike95490 Posts: 7,970Solar Expert ✭✭✭✭
    Re: Multiple Inverter Hookup
    andy300z wrote: »
    ...
    I will like to know if i can use this for my sump pump and is this safe to do since the ground shows open on my ground detector can this lead to a shock hazzard since the pump is completely submerged in water.

    Thanks


    Never stand in the water to touch the pump.

    And I don't know, but maybe you should not ground the case of the inverter, unless it has a label and screw for that. Or when the pump hits the water, the sparks exit the inverter.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • andy300zandy300z Posts: 39Solar Expert
    Re: Multiple Inverter Hookup

    The instruction clearly states to ground the unit to earth with the provided terminal, which i did. I am just puzzled that the plug in ground detector shows and open ground.
  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Multiple Inverter Hookup

    Just for the record, most motor loads don't like running on modified sine wave inverters

    Tony
  • mike95490mike95490 Posts: 7,970Solar Expert ✭✭✭✭
    Re: Multiple Inverter Hookup
    andy300z wrote: »
    The instruction clearly states to ground the unit to earth with the provided terminal, which i did. I am just puzzled that the plug in ground detector shows and open ground.

    that's because both leads are "hot" at about 60Vac You can't ground the leads.

    Just for the record, most motor loads don't like running on modified sine wave inverters

    And have you tested the pump on the mod-sine inverter ? it will run 20% hotter.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • andy300zandy300z Posts: 39Solar Expert
    Re: Multiple Inverter Hookup

    Luckly this puppy runs i am just concerned about the shock hazard/safety that goes with this type of set up. My basement was flooded due to lost of power.
  • andy300zandy300z Posts: 39Solar Expert
    Re: Multiple Inverter Hookup
    mike90045 wrote: »
    that's because both leads are "hot" at about 60Vac You can't ground the leads.




    And have you tested the pump on the mod-sine inverter ? it will run 20% hotter.

    What happens if there is a short in the pump while its running ?
  • mike95490mike95490 Posts: 7,970Solar Expert ✭✭✭✭
    Re: Multiple Inverter Hookup
    andy300z wrote: »
    What happens if there is a short in the pump while its running ?

    Sparks come out of the inverter, and the proper size fuse in it's power line stops that in a second.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Posts: 28,087Super Moderators, Administrators admin
    Re: Multiple Inverter Hookup

    Grounding electrical boxes/equipment is to prevent the exposed metal from becoming "hot" with respect to ground. If a "hot lead" (with respect to ground) contacts the exposed metal, there is supposed to be sufficient current flow to trip the circuit breaker.

    Similar to grounding the negative post of a battery system... If there is a + to sheet metal short, the sheet metal should be grounded and the over current will pop the DC fuse and prevent the wiring from over heating and causing a fire.

    There is (almost never) a need to ground the DC or the AC circuits for "proper" operation. Grounding is purely to reduce the chances of electrical shock.

    OK--Safety grounding around pumps and inverters--My take/understanding--Do not violate code based on what I say--just my 2 cents worth of opinion.

    Starting with (most) True Sine Wave Inverters... They have a full isolation transformer from the DC to AC side--So the AC power leads are both floating unless specifically tied to earth ground (earth ground bonded neutral or sometimes grounded inside in the inverter).

    A purely floating AC output (transformer isolated output) is actually pretty safe. A person can touch EITHER hot lead and ground/return and not get a shock. In some uses, this is actually an anti-shock safety factor.

    If you ground one lead of the AC output, then it becomes just like normal AC house wiring.

    With Sine Wave Inverters, you can use a GFI (Ground Fault Interrupter) which measures the current flow on the Hot and Return line for AC power (small transformer). If the current flow becomes "unbalanced" by more than ~0.005 amps--it is assumed that some of the energy is leaking to earth ground--possibly through a human and shuts down.

    Also, with your inverter--The ground plug should be tied to frame ground on the inverter (check with an ohm meter)... But the two 120 VAC leads may show no ground connection at all when using a little 3 light circuit tester. Nothing wrong--Just what you would see with a floating AC output.

    With (most) MSW (Modified Square Wave) Inverters, they do not have an isolation transformer, but instead have a direct connection from the Battery DC to AC output through the power transistors.

    This means, that if the DC battery bank is grounded, the two 120 VAC MSW outputs are also ground referenced back to the battery. And, if you make a connection between either 120 VAC connections to DC/Earth Ground, you will measure ~60 VAC and would have heavy current flow (i.e., basically a short circuit) from Battery positive lead, through the inverter to earth ground / DC return... You may pop a fuse or breaker, and/or damage the MSW inverter.

    So, an MSW inverter should not have a 120 VAC output lead "turned into a neutral" by connecting to Earth Ground--Especially if the Battery Bank is also ground referenced.

    As I understand, an MSW inverter with a GFI outlet is more likely to false trip because of the MSW wave form (I think I remember reading that).

    What would I do for a sump pump... Two perfectly valid setups for TSW inverters with floating AC outputs (you may choose to DC ground the Battery Bank not--does not affect the safety of the inverter output. Typically you would ground the inverter's metal case back to the Battery Bank ground to protect against and inverter internal short from energizing the case--exposed sheet metal):
    1. Simply connect the AC output of the inverter to the Pump... Isolated/floating AC, would be very difficult to shock yourself.
    2. Make a Grounded Neutral for the AC TSW output, place a GFI protected outlet on the TSW inverter and connect the pump. If there is an insulation failure in the hot side of the circuit, the GFI will trip and turn of the power to the pump. If you get a shock, it should be mild and power will be turned off quickly.
    For my two cents, if I was protecting my basement from flooding--I would choose #1--It is safe and if there is a minor insulation failure, the AC power will not shutdown the pump and flood the basement.

    If there is an AC short (hot leads shorted)--The inverter/breaker/fuses should pop and prevent a fire (from overheated wiring).

    For the MSW inverter--You don't have much choice... You cannot ground reference the outputs. And they will be ground referenced by the battery bank if it is grounded to earth/water pipe.

    You can try placing a GFI on the MSW output and see if the pump still works reliably.

    In either case, if you are very concern about reliability, I would not install a GFI on the AC output of the MSW inverter.

    And if you are concerned about electric shock, I would probably not ground reference the battery bank--that would let the AC leads "float" with respect to ground.

    If there are any Hot to Ground shorts--with a floating DC battery bank, there will be no short circuit current flow.

    Notice that there is no indication of an AC output to Ground short--Sort one of the drawbacks to a "floating output system"... In cases where it matters, there may be some test lights or equivalent to see if there are any power to ground faults (turn on test light to check AC hot to ground connection--if lights, there is a short in your "floating" circuit--if bulb stays dark, output is still floating).

    This is an issue with either TSW or MSW floating outputs (lack of a positive safety test feature).

    If the battery bank is grounded--Then there will be current flow and you will pop a fuse/breaker and possibly damage the MSW inverter. But the "failures" should be "safe" (no fire).

    I am not sure if I would ground reference the battery bank with an MSW inverter--I would probably leave it floating in my home assuming wood frame construction (no metal to energize vs an RV with a steel frame and aluminum siding).

    If this was in a metal framed structure (steel building, RV, etc.), I would ground reference the battery bank.

    -Bill "way too much typing" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • andy300zandy300z Posts: 39Solar Expert
    Re: Multiple Inverter Hookup

    Thanks bill for that well taught lecture . I taught i was in college again
    Appreciated!!!
Sign In or Register to comment.