Using two ProSine 1800 inverters - can a neutral be shared?

I have two ProSine 1800 GFCI inverters and am trying to wire them into my breaker panel. One half of my panel is fed from one leg of my utility and the other half is fed from the other leg of my utility company; both share a common neutral wire. I have no 240V loads, only 120V loads.

I am trying to use one ProSine on one leg and a second on the other leg but I believe the common neutral is causing problems. I can power up each separately and they work fine but I cannot activate both at the same time without the internal GFCI tripping. Can I replace both ProSine GFCI's with standard outlets and if so will this solve the problem? My in-house outlets are already protected with their own GFCI's.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Using two ProSine 1800 inverters - can a neutral be shared?

    Welcome to the forum.

    Your suspicions are correct: the combination of two GFCI units sharing neutral plus a N-G bond before the outlets is causing problems.

    These inverters aren't designed for hard-wiring, obviously. They don't meet code for a fixed installation either. That aside, you need to remove both GFCI outlets and the N-G bonds within each inverter (as there is probably such a bond in the service panel already).

    I don't know why you are doing this as you have grid power already and I have to caution that there are many potential problems with trying to replace the utility power with two small inverters.

    If you are looking for back-up power, isolate only those circuits you need it on using a sub-panel and make the grid to inverter change there. Don't try to energize the whole house.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Using two ProSine 1800 inverters - can a neutral be shared?
    Welcome to the forum.

    Your suspicions are correct: the combination of two GFCI units sharing neutral plus a N-G bond before the outlets is causing problems.
    ...
    If you are looking for back-up power, isolate only those circuits you need it on using a sub-panel and make the grid to inverter change there. Don't try to energize the whole house.
    In addition, the current through the shared neutral wire will be up to twice the current in each of the hot wires, unlike the zero to hot amperage the original split phase feed produces. As long as the shared neutral is only in the house wiring and each inverter's capacity is small (less than 1200 watts) this is not likely to be a problem.

    Also, any 240 volt loads powered from the panel will not work, seeing a voltage varying from zero to 240 volts as the synchronization between the two inverters changes. Any motor loads will risk damage if turned on under these conditions.
    SMA SB 3000, old BP panels.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Using two ProSine 1800 inverters - can a neutral be shared?

    Fortunately he says he hasn't got any 240 loads.

    The current on the neutral shouldn't be a problem either, as there would only be 15 Amp circuits coming from the main box and each would have its own neutral line so the only part that would really be shared is the neutral bus which is well able to handle the 30+ Amps of both inverters.

    The biggest problem is likely to be overloading the inverters as each would have multiple 15 Amp circuits on it and they're only capable of handling one apiece.
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Using two ProSine 1800 inverters - can a neutral be shared?

    A very simple solution is to simply remove one of the hot legs, and put a jumper in, so that all the loads are powered from a single leg. This way you could switch freely between inverter and grid. There could be some special cases, such as kithchen split receptacles, where neutral is shared between two circuits. Re-wiring will double current through such neutrals, so there might be a problem.

    The other idea is to sell ProSines and buy two stackable inverters, or one 240V inverter.
  • jwitzeljwitzel Registered Users Posts: 2
    Re: Using two ProSine 1800 inverters - can a neutral be shared?
    Welcome to the forum.

    Your suspicions are correct: the combination of two GFCI units sharing neutral plus a N-G bond before the outlets is causing problems.

    These inverters aren't designed for hard-wiring, obviously. They don't meet code for a fixed installation either. That aside, you need to remove both GFCI outlets and the N-G bonds within each inverter (as there is probably such a bond in the service panel already).

    I don't know why you are doing this as you have grid power already and I have to caution that there are many potential problems with trying to replace the utility power with two small inverters.

    If you are looking for back-up power, isolate only those circuits you need it on using a sub-panel and make the grid to inverter change there. Don't try to energize the whole house.

    Thanks for the advice. Actually my "home" is a trawler I am living and traveling on; the only time I am on the grid is when I am docked which isn't too often. I have an 18 battery deep-cycle bank and most all of my energy comes from four large solar panels I have over the fly bridge; a diesel generator provides emergency power. Unfortunately the way the boat is wired it would be difficult to separate the neutrals so removing the GFCI's from the ProSine's is the best solution. One last question though, why do I need to remove the N-G connection in the ProSine's? Wouldn't it just become a redundant connection if my panel also has a N-G termination?
  • Joe_BJoe_B Solar Expert Posts: 318 ✭✭✭✭✭✭
    Re: Using two ProSine 1800 inverters - can a neutral be shared?

    I believe that some of the higher end prosine inverters had a sync jack that allowed them to be synchronized with each other. This will make the slave inverter always be 180 degrees out of phase with the master.
  • PhotowhitPhotowhit Solar Expert Posts: 5,806 ✭✭✭✭✭
    Re: Using two ProSine 1800 inverters - can a neutral be shared?
    NorthGuy wrote: »
    A very simple solution is to simply remove one of the hot legs, and put a jumper in, so that all the loads are powered from a single leg...

    This would limit him to using only one inverter.

    I hope to do much the same thing, with the same inverters, though mine are made to be hardwired and at least the one carrying the UL1741 isn't bonded. I hope you understand you'll need a substantial battery bank to run more than 1000 watts for very long, I won't need more than 1 other than running 2 A/C's during the day, when most or all of the energy will be used from energy input from the sun. I wouldn't want to run more than 1000 watts from my 24 volt 800 Amp hour battery for very long.

    I purchased an Iris 1800 watt inverter, which is a modified Prosine 1800 that is bonded and has GFCI outlets. I intend to remove the bond on this so it can replace the Prosine I took from my cabin. If I'll take some photos if I get there first. Of course my job, which cut me back to 16 hours for 4 months, now has me working 7 days a week and 12 hour day currently.

    FWIW - I will only 'need' my 2 inverters during the day when I will draw most of my power via the sun, Drawing more than 1000 watts from my 24 volt 800 watt battery bank would be undesirable for any length of time. What does your system look like?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Using two ProSine 1800 inverters - can a neutral be shared?
    jwitzel wrote: »
    Thanks for the advice. Actually my "home" is a trawler I am living and traveling on; the only time I am on the grid is when I am docked which isn't too often. I have an 18 battery deep-cycle bank and most all of my energy comes from four large solar panels I have over the fly bridge; a diesel generator provides emergency power. Unfortunately the way the boat is wired it would be difficult to separate the neutrals so removing the GFCI's from the ProSine's is the best solution. One last question though, why do I need to remove the N-G connection in the ProSine's? Wouldn't it just become a redundant connection if my panel also has a N-G termination?

    Well you just came up roses!
    Not in a house = Prosine okay. So it's a matter of what size service panel your working with, and where/how the existing N-G bond is. Often for a boat or RV the N-G bond is lifted when shore power is connected because that power source has one. Your boat may have no such bond, as there isn't really an Earth ground available on the water.

    The thing is when you have multiple bonds you create loops that can be alternate current paths. This is the #1 way GFCI trip falsely, btw: there's an N-G bond on either side of the GFCI which allows some of the current to travel on the ground rather than the neutral, so the GFCI will see an imbalance between hot and neutral current.

    Do you have a transfer switch for going between inverter and shore power? And how is the generator connected to all this?
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Using two ProSine 1800 inverters - can a neutral be shared?
    jwitzel wrote: »
    Thanks for the advice. Actually my "home" is a trawler I am living and traveling on; the only time I am on the grid is when I am docked which isn't too often. I have an 18 battery deep-cycle bank and most all of my energy comes from four large solar panels I have over the fly bridge; a diesel generator provides emergency power. Unfortunately the way the boat is wired it would be difficult to separate the neutrals so removing the GFCI's from the ProSine's is the best solution. One last question though, why do I need to remove the N-G connection in the ProSine's? Wouldn't it just become a redundant connection if my panel also has a N-G termination?
    Why would your panel have a Neutral - Ground bond ?? You get that bond from your shore power cord for your panel. Your Inverter gives you the bond when inverting and you should have a ground plate on the hull to ground the chassis. What does your Generator ground to ??
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Using two ProSine 1800 inverters - can a neutral be shared?

    What are your loads? I understand you don't have any 240 volt loads, are your 120 volt loads so large that you need two inverters? If not, and if you have a transfer switch, you can wire the transfer switch so that when you switch over to inverter power, one single inverter will feed in on both hot legs of your distribution panel. Food for thought and very simple.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Using two ProSine 1800 inverters - can a neutral be shared?

    actually my take on this is that he just wants to power things using a handy everyday utility box rather than have 2 separate 120vac boxes. the real problem is not the sharing of an ac leg so much, but the real problem could rear its ugly head through the sharing of the same battery bank. it's a possible backdoor short waiting to happen. this is something i can't say is feasible to do as i'm not sure if it can be done without fireworks so my advice is to ask those that made the inverters. hope they do answer your question and i'd be real curious of what they'd say so should they answer then please let us know what was said.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Using two ProSine 1800 inverters - can a neutral be shared?

    What Niel said is about 100% certain with an MSW type inverter. The Prosines are pure sine wave, though, and should not suffer the potential shorting problem (shared DC and one shared AC connection). Never hurts to check with the maker, just in case.
  • waywardpawwaywardpaw Registered Users Posts: 1
    Re: Using two ProSine 1800 inverters - can a neutral be shared?

    I am somewhat new at this, but with 800AH at 24V, that is 19.2kWh of battery capacity, which would seem to allow about 1.92kW draw for up to 10 hours. So why would only 1kW draw be undesirable, even considering inverter inefficiency?
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Using two ProSine 1800 inverters - can a neutral be shared?
    waywardpaw wrote: »
    I am somewhat new at this, but with 800AH at 24V, that is 19.2kWh of battery capacity, which would seem to allow about 1.92kW draw for up to 10 hours. So why would only 1kW draw be undesirable, even considering inverter inefficiency?

    You do not want to draw down your battery bank below 50% except in an emergency, as it has a disproportionate effect on the cycle life of the batteries.
    To allow for recharging after a cloudy day or two without running a generator, you do not want to routinely go below 80%. That gives you about 4kWH, or 1kW for four hours.
    The other issue is that for an FLA battery you do not want to discharge at more than the 10 hour rate to control heating and Peukert losses. That would limit you to 1.92kW, but with a duration of 2 hours or less.
    SMA SB 3000, old BP panels.
  • PhotowhitPhotowhit Solar Expert Posts: 5,806 ✭✭✭✭✭
    Re: Using two ProSine 1800 inverters - can a neutral be shared?
    waywardpaw wrote: »
    I am somewhat new at this, but with 800AH at 24V, that is 19.2kWh of battery capacity, which would seem to allow about 1.92kW draw for up to 10 hours. So why would only 1kW draw be undesirable, even considering inverter inefficiency?

    To expand on what the Fizzycist said, basically at a 10 hour rate, you have less run time, my battery which is rated at 804 AH at a 20 hour rate is only a 510Ah battery at a 6 hour rate.

    I like to live in the top 20% of the battery capacity, during the summer months I might well push that to top 50 - 60% when I have enough sun to fully recharge the battery during the day.

    The 1000 watt draw represents roughly a 20hr discharge rate.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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