Neutral & Ground Inverter Wiring

david3
david3 Solar Expert Posts: 37
While reading an inverter manual, specifically the new Outback Radian manual (though I think this may apply to some others as well), it looks like the inverter requires a neutral connection to function.

I've got 220V 60Hz (two 110V legs) at my house, and have a safety ground to my own grounding rod, but no neutral from the utility.

If I were to wire the neutral connections (and ground) on the inverter to my grounding rod, would that allow the inverter to work properly, or cause any problems? The neutral wouldn't be extended into my house.
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Comments

  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Neutral & Ground Inverter Wiring
    david3 wrote: »

    I've got 220V 60Hz (two 110V legs) at my house, and have a safety ground to my own grounding rod, but no neutral from the utility.

    You've got 220 volts, consisting of two 110 volt legs from your utility, but no neutral from the utility? :confused:
  • david3
    david3 Solar Expert Posts: 37
    Re: Neutral & Ground Inverter Wiring
    You've got 220 volts, consisting of two 110 volt legs from your utility, but no neutral from the utility? :confused:

    Yes, that is correct. This is in the Philippines.
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Neutral & Ground Inverter Wiring

    Get the utility to drop you a neutral. If there are two 110v legs, then there is a neutral at the transformer.
  • david3
    david3 Solar Expert Posts: 37
    Re: Neutral & Ground Inverter Wiring

    I could check to see if they'd be willing to give me a neutral, but I'd highly doubt they would, unless I wanted to buy my own transformer from them, in which case I imagine they'd let me do as I wish.

    I checked into getting my own transformer when we built the house 6 years ago, and I don't remember exactly how much it was, but it was expensive, perhaps around $5,000 USD or more.
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Neutral & Ground Inverter Wiring

    Is there a separate ground wire brought from transformer?

    I don't understand your statement of "two 110 v lines".

    There is no way 110 vac can be supplied with one forward wire and earth return. There would be too much resistance on the earth return.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Neutral & Ground Inverter Wiring
    david3 wrote: »
    This is in the Philippines.
    Wow! Not kidding, I'd sure like to understand the electrical distribution system there. Sounds totally unlike anything I could ever dream up.
  • nsaspook
    nsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Neutral & Ground Inverter Wiring

    When I lived there about 20 years ago the power to my house was 220AC ungrounded from the pole transformer. We had several 220AC to 110AC variable tapped transformers to run US 110 electrical products. Local hardware stores sold variable tapped transformers to adjust the voltage to normal because the 220AC varied by a huge amount daily when there wasn't a total blackout for hours due to overloads on the local utility.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Neutral & Ground Inverter Wiring

    hmmm. almost sounds like he has a large isolation transformer, but with a split secondary to break it down to 2 110v legs.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Neutral & Ground Inverter Wiring
    niel wrote: »
    hmmm. almost sounds like he has a large isolation transformer, but with a split secondary to break it down to 2 110v legs.

    You mean a transformer with two separate "half Voltage" secondary windings as opposed to one center-tapped winding? That would be difficult to deal with if the windings were out of phase (and likely would be). Worse than just 220 VAC with no neutral and relying on Earth ground to supply 110.

    Makes you glad to be living someplace where the biggest problem is a +/- 10% line Voltage. :roll:
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Neutral & Ground Inverter Wiring
    You mean a transformer with two separate "half Voltage" secondary windings as opposed to one center-tapped winding? That would be difficult to deal with if the windings were out of phase (and likely would be). Worse than just 220 VAC with no neutral and relying on Earth ground to supply 110.

    Makes you glad to be living someplace where the biggest problem is a +/- 10% line Voltage. :roll:

    by split isolation transformer i meant a center tapped secondary 1:1 transformer.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Neutral & Ground Inverter Wiring
    niel wrote: »
    by split isolation transformer i meant a center tapped secondary 1:1 transformer.

    With the CT connected to ground that should work fine for providing proper 110/110. Shouldn't it?
    (It's been one of those days: I may be thinking of something else.) :blush:
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Neutral & Ground Inverter Wiring

    While North America makes a lot of safety decisions/designs based on grounded neutrals.

    For inverters/power systems--having a ground referenced power lead does not really affect day to day operations--Except in some cases.

    One of those cases is that some vendors of UPS's will not start if they do not see a ground/grounded neutral connection on the AC input. However, once the inverter is "started", they usually will stay operational even if the AC plug is removed from the wall.

    Some of the AC Transfer switches are two or three pole (for 120/240 VAC split phase power) which that allows you to switch the grounded neutral leg too... For example, if you are using a MSW inverter which tends to not like grounded neutrals + ground referenced battery power (negative or positive ground reference) or in the case of shore power vs off-grid power where you want to frame ground your neutral with a TSW inverter.

    You can run both the Hot and the Neutral through the transfer switch. When running from Grid Power (or shore power), the neutral (and assumed ground) is carried through to the downstream branch circuits.

    When the AC power fails, the switch transfers to the local inverter which then may have a floating neutral (in the case of a shore power connect where ground bond is made outside the RV/Boat), to the TSW Inverter with its neutral bonded to the local frame/safety ground.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nsaspook
    nsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Neutral & Ground Inverter Wiring
    With the CT connected to ground that should work fine for providing proper 110/110. Shouldn't it?
    (It's been one of those days: I may be thinking of something else.) :blush:

    I should explain that grounded power from the utility there means only a hot wire and neutral come from the pole. In theory the neutral wire was earth grounded somewhere so the secondary was not floating but often it was missing or the wire had been stolen long ago so having your own grounding rod at the house was a very good idea. I knew one guy who had paid the money for a US style power transformer but that was rare and expensive just like this persons was.
    http://www.livingincebuforums.com/ipb/topic/3883-i-just-got-my-own-transformer-from-veco/page__p__26487__fromsearch__1#entry26487

    http://www.livingincebuforums.com/ipb/topic/22999-philippine-electrical-wiring/
  • david3
    david3 Solar Expert Posts: 37
    Re: Neutral & Ground Inverter Wiring
    RCinFLA wrote: »
    Is there a separate ground wire brought from transformer?

    I don't understand your statement of "two 110 v lines".

    There is no way 110 vac can be supplied with one forward wire and earth return. There would be too much resistance on the earth return.

    There's not a separate ground wire brought from the transformer. The ground that I have is to a grounding rod at my house, for safety. It took some doing to convince the electrician to wire a ground to our outlets, since it's not normally done here.

    Perhaps "two 110v legs" is inaccurate, but they're at least two hot legs -- neither is a neutral or ground. Together they're 220v. When I measure from 1 leg to my house ground, the voltage on the two legs sometimes vary.

    I measured last night and it was approx. 190V on one leg and 30V on the other, and when I measured this morning it was approx. 200V on one leg and 20V on the other. When it was checked a few years ago I don't remember it being that different.
    nsaspook wrote: »
    When I lived there about 20 years ago the power to my house was 220AC ungrounded from the pole transformer. We had several 220AC to 110AC variable tapped transformers to run US 110 electrical products. Local hardware stores sold variable tapped transformers to adjust the voltage to normal because the 220AC varied by a huge amount daily when there wasn't a total blackout for hours due to overloads on the local utility.

    That's right. Most of our appliances are 220V, and for the 110V electronics we use step-down transformers.

    While there doesn't seem to be one standard for electricity here, I think it's most common to have 1 hot, insulated 220V line wrapped around an uninsulated neutral line going to the house.

    But in some cities, like the one I'm in, it's 2 hot, insulated lines to supply 220V, with no neutral, and no ground. I'm guessing the transformers used are similar to those in the U.S., but the neutral hasn't been connected.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Neutral & Ground Inverter Wiring
    david3 wrote: »
    I'm guessing the transformers used are similar to those in the U.S., but the neutral hasn't been connected.

    Ah, now I understand. Straight, ungrounded 220 delivered right to the home.
    Thanks for that.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Neutral & Ground Inverter Wiring

    david3;

    This makes a lot of sense, thanks!
    You have a 220 VAC 60 Hz system. No 110 legs, because there is no center-tapped "neutral" reference point. If you measure between one of the leads and Earth ground you will get a lot of different Voltages, depending on conditions. The same thing happens here if the neutral line is broken. The step-down transformers make sense too. This set-up is not dissimilar from the 230 VAC 50 Hz used in Europe, although they usually include an Earth ground at the outlets.

    Now back to the original question: will the Radian work from this? I would check with outback directly, but there is the possibility it would not. Since that inverter is designed to work with the standard power available in NA, it is expecting the split phase for its input and grid-tie function. I'm still reading up on it, but it appears to need a 240 VAC generator input and the grid-tie data is given as Voltage reference to either L1 or L2 (from neutral). If you don't use the GT function it may be possible to use your 220 Volt utility power as a "generator" for it, as most generators have a "floating neutral".

    Could work, but I'd want Outback's official word on it before I spent the money. Otherwise you'd have to do as has been suggested and get a 1:1 CT transformer capable of handling the total power.

    It's a very promising product, from the looks of things.
  • david3
    david3 Solar Expert Posts: 37
    Re: Neutral & Ground Inverter Wiring

    Thanks Cariboocoot.

    This is what the Radian manual says about the Generator mode:
    Generator:

    This mode allows the use of any generator, even one with a rough or imperfect AC waveform. In other modes, a “noisy” or irregular waveform may not be accepted by the inverter. This mode allows these waveforms to be accepted. The charging algorithm of this mode is designed to work well with any AC generator regardless of power quality or regulation mechanism. The generator must still comply with the inverter’s nominal input specifications in the Input section of this manual.

    Reading the troubleshooting section, I have my doubts it would work, though:
    Symptom: Will not connect to the AC source.

    Possible Cause: AC source is not 120/240 Vac split-phase, or the AC source neutral is not connected to the inverter.

    Possible Remedy: Confirm the nature of the AC source. Check the AC voltage between L1, L2, and neutral on the inverter’s input test points. (See page 33.) L1-neutral and L2-neutral voltages should be 120 Vac. L1-L2 voltage should be 240 Vac. Other voltages or combinations, such as two phases of a three-phase source (208 Vac), or 240 Vac without a neutral, will not be accepted.
    Symptom: Unusual and different voltages on AC hot input lines.

    Possible Cause: Input neutral is not connected correctly. The inverter also may not connect to the AC source.

    Possible Remedy: Test L1 input and NEU connections with AC voltmeter. Test L2 input and NEU connections with AC voltmeter. (This can be on Grid or Gen input, depending where the symptoms appear.) Test L1 to L2 input. From hot to neutral should be approximately 120 Vac. L1 to L2 should be approximately 240 Vac. If the two legs are different voltages but still add up to 240 Vac, the neutral is not connected to the inverter.

    I'd be hesitant to use a European-style inverter, since our power is 60hz, and my house is wired for two hot lines, not a hot+neutral.

    It sounds like I'd probably need to get my own transformer from the utility with a neutral connection, or isolate the utility and PV systems with an automatic transfer switch that could switch back to the utility when my batteries are low, though that wouldn't let me use the charger built into the inverter.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Neutral & Ground Inverter Wiring

    I'm reading through the Radian info this evening. There is part of the install manual that implies it would accept 120 Volts from a generator. If so, running your 220 through a step-down transformer to 110 would "look" like 120 VAC generator output.

    Tricky thing, the difference between single phase waveform and split phase (two parallel) waveform.

    I'm liking many of the features on this Radian unit, but also disliking some of them.

    And no you shouldn't use a 50Hz unit - it's too far off from 60Hz for most things.

    You could run the 220 VAC to a standard battery charger to the battery bank, but that would be wasting the built-in charger you paid for. :cry:
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Neutral & Ground Inverter Wiring

    david,
    i am still not 100% clear on how it is done there. for the power coming from the pole, does it have a ground wire going to a ground rod at all? remember i'm talking of at the utility pole. if you grounded yours then how did you ground it? also, did i get it right that you are using a 1:1 transformer with a secondary center tap that will give 110vac across the center to either end, but a full 220vac across the outer leads?
  • david3
    david3 Solar Expert Posts: 37
    Re: Neutral & Ground Inverter Wiring

    Niel,

    There is no ground wire from the utility pole at all, just two hot lines.

    My grounding is separate, and wouldn't ordinarily even be done here. I've got a grounding rod at my house that is wired to the the ground on my outlets (that are similar to the U.S. outlets, except 220V).

    I'm not completely clear on what the utility transformer looks like or how it's wired.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Neutral & Ground Inverter Wiring

    my comments in bold.
    david3 wrote: »
    Niel,

    There is no ground wire from the utility pole at all, just two hot lines.

    i understand there isn't any ground wires coming from the pole to your place, but i wanted you to verify there isn't a wire going down the pole itself to a rod right at the pole.

    My grounding is separate, and wouldn't ordinarily even be done here. I've got a grounding rod at my house that is wired to the the ground on my outlets (that are similar to the U.S. outlets, except 220V).

    if i get this correctly the ground wire you have isn't really doing anything at all as just running that 3rd wire from the outlet to a ground rod does next to nothing for you.

    I'm not completely clear on what the utility transformer looks like or how it's wired.

    he's a pic below of 3 transformers one might see around here.

    in the pic you will note there are 3 wires atop the pole. (hard to see but 2 on top cross arm and 1 off the top of the pole itself) are there 3 wires atop the poles where you are?
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Neutral & Ground Inverter Wiring
    niel wrote: »
    in the pic you will note there are 3 wires atop the pole. (hard to see but 2 on top cross arm and 1 off the top of the pole itself) are there 3 wires atop the poles where you are?

    Niels,

    You are really going to confuse things. The picture shows a three phase feed, likely in a commercial area. There is no primary side transformer return for this config as the three phase lines are likely be connected as delta individual phases to the three transformers' primaries below in the picture. The secondary of the transformers would have the 240v split phase via a center tap on secondary to provide neutral to customer.

    In normal residential areas the three phase feed is usually split up at entrance to neighborhood and a neutral wire must then be supplied to the 25kV hot single phase breakoff. This fans out as three separate lines from the original three phase coming into residential area. So it is a single phase feed down a given street.

    It sounds like he has a normal split phase secondary transformer but the center tap neutral is just connected to earth ground at the pole for lightning protection. This is somewhat common for 220vac only service.

    If he sees the grounding wire going down the side of the pole (typically just wrapped around the butt of pole in earth), and he could bury a wire from his ground rod to the pole's ground rod, then he has the wired split phase connection. This pole ground wires are usually small gauge, like #8 so his 120vac loads should be limited to 20 to 30 amps total depending on run length between his ground and pole's ground rod.

    This is not exactly legal but there is little danger in doing it.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Neutral & Ground Inverter Wiring
    RCinFLA wrote: »
    Niels,

    You are really going to confuse things. The picture shows a three phase feed, likely in a commercial area. There is no primary side transformer return for this config as the three phase lines are likely be connected as delta individual phases to the three transformers' primaries below in the picture. The secondary of the transformers would have the 240v split phase via a center tap on secondary to provide neutral to customer.

    In normal residential areas the three phase feed is usually split up at entrance to neighborhood and a neutral wire must then be supplied to the 25kV hot single phase breakoff. This fans out as three separate lines from the original three phase coming into residential area. So it is a single phase feed down a given street.

    It sounds like he has a normal split phase secondary transformer but the center tap neutral is just connected to earth ground at the pole for lightning protection. This is somewhat common for 220vac only service.

    If he sees the grounding wire going down the side of the pole (typically just wrapped around the butt of pole in earth), and he could bury a wire from his ground rod to the pole's ground rod, then he has the wired split phase connection. This pole ground wires are usually small gauge, like #8 so his 120vac loads should be limited to 20 to 30 amps total depending on run length between his ground and pole's ground rod.

    This is not exactly legal but there is little danger in doing it.

    yes, you're right, i may be confusing him, but transformers generally looks like those. i was also trying to stress that there most likely is a ground lead on the pole and was trying to get him to see if it is there. 3 wires usually is indicative of a ground lead and if it is there he can do as you suggest or see if an electrician would make an exception and run a full sized ground wire from the pole to his home so he can have the full benefit of our type appliances and protections. does that make sense?
  • david3
    david3 Solar Expert Posts: 37
    Re: Neutral & Ground Inverter Wiring

    Niel,

    I'm not even sure where the transformer is that serves our house, but I haven't noticed any utility poles with grounding wires running down the pole here. I'll try to take a closer look the next time I go out, though.

    The ground wire I have is just a safety ground, so that the electronics with the 3-prong plugs can be grounded.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Neutral & Ground Inverter Wiring

    i'm taking stabs in the dark trying to be sure of your setup there and for us to second guess things is too risky to you, but you may want to express this all to your utility or a good local electrician and mention the reason why is to make some of this foreign equipment more compatible and safe to operate there. outback may not even have answers for you if they aren't sure of how the grid is done over there.

    once you find out the answers you seek, please tell us out of curiosity.
  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Neutral & Ground Inverter Wiring

    An option to consider is a double-conversion UPS. You can get them very cheap (I've bought 2 in the last few years for under $200 USD), and at high wattages, like 8 kw. They can be set to output a different voltage than their input voltage - only downside is then they won't allow a bypass to the utility but that's no big deal for a specialized load like this. This would allow you to input say 220 volts single phase at 50 Hz, but output 120/240 split phase 60 Hz.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Neutral & Ground Inverter Wiring
    techntrek wrote: »
    An option to consider is a double-conversion UPS. You can get them very cheap (I've bought 2 in the last few years for under $200 USD), and at high wattages, like 8 kw. They can be set to output a different voltage than their input voltage - only downside is then they won't allow a bypass to the utility but that's no big deal for a specialized load like this. This would allow you to input say 220 volts single phase at 50 Hz, but output 120/240 split phase 60 Hz.
    I've never seen one of these. How do they convert frequency?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Neutral & Ground Inverter Wiring

    They do not have a "pass thru" mode. They are simply a battery charger=>battery=>inverter configuration.

    Much less chance of input power junk from getting through to your loads--But much less efficient.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Neutral & Ground Inverter Wiring

    They do have a bypass (pass-through) ability, but as I mentioned above if you don't have the input and output settings identical it won't allow it to happen. Overload, or internal fault, or a manual command will all trigger a bypass.

    The one I just bought last week has a 92% efficiency at full load - not nearly the penalty they used to have (my older one is 87%). Since that is with the double conversion if you are only feeding it with a battery/solar configuration (no AC input) the inverter alone must be equivalent to today's stand-alone inverters in the mid 90's.

    Here is a link to the one I got from eBay last week: http://www.apc.com/resource/include/techspec_index.cfm?base_sku=SURT10000XLT

    This describes the various types of UPSs: http://en.wikipedia.org/wiki/Uninterruptible_power_supply#Technologies
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • david3
    david3 Solar Expert Posts: 37
    Re: Neutral & Ground Inverter Wiring

    Thanks for the idea techntrek. That 10 KVA Smart-UPS looks like it's around $5,000+ USD new.

    I wonder if there are other inverters that can handle the 2-line 220V 60Hz without the neutral wire.

    I looked at a few grid-tie inverter manuals for SMA Sunny Boy and Frontius and if appears (if I understand correctly) that they would support 2-line 220V 60Hz without the neutral wire.

    With the SMA Sunny Boy, for example, they mention a "240V Delta No Neutral" configuration settable via DIP switches.

    From the SB4000US manual:
    The Sunny Boy comes from the factory pre-configured for utility interconnection with neutral. The Sunny Boy may be reconfigured for grids without neutral by setting the jumpers on the board of the Sunny Boy.

    Net metering with a grid-tie inverter and a good 1800 rpm diesel generator on an automatic transfer switch for backup could work.

    I found there is actually an Act passed in 2008 in the Philippines that requires utilities to allow Net Metering, so it might be a possibility. However, I'm not a lawyer.

    http://www.lawphil.net/statutes/repacts/ra2008/ra_9513_2008.html

    I met with an engineer from our electric utility to ask him about Net Metering and any requirements for it they might have. Apparently I'm the first person in the city to want to do grid-tie/net metering for a PV system, and he hadn't heard of the law, so they'll have to check into it some more. Haven't heard back, yet.