inverter to AC breaker box (off-grid)

bobdogbobdog Posts: 191Solar Expert ✭✭✭✭✭
I just read this:

13. How can DC-AC inverters be connected to multi-wire branch circuits?

Do not directly connect the hot side of the inverter to the two hot legs of the 120 / 240 VAC electrical breaker panel / load centre where multi-wire ( common neutral ) branch circuit wiring method is used for distribution of AC power. This may lead to overloading / overheating of the neutral conductor and is a risk of fire. A split phase transformer (isolated or auto-transformer ) of suitable wattage rating ( 25 % more than the wattage rating of the inverter ) with primary of 120 VAC and secondary of 120 / 240 VAC ( Two 120 VAC split phases 180 degrees apart) should be used. The hot and neutral of the 120 VAC output of the inverter should be fed to the primary of this transformer and the 2 hot outputs ( 120 VAC split phases ) and the neutral from the secondary of this transformer should be connected to the electrical breaker panel / load centre.


This is from a the Samlex website. I'm confused as I wanted to do just that, distribute power to various circuits in the cabin. So, is this just with this inverter (600 watt heavy) or Samlex or all inverters with plugs? If so, how do I run AC power throughout my house w/o runnnig a bunch of ext. cords? :confused:

Are Samlex made overseas?
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Comments

  • icarusicarus Posts: 5,070Solar Expert
    Re: inverter to AC breaker box (off-grid)

    The reason you shouldn't connect the inverter to both sides of a 240 split phase panel is that certain wiring methods allow 2 circuits to share a neutral as long as they are on different phases, thereby allowing the neutral to essentially carry double the current that any give size wire would be rated at. By being on different phases, the neutral load would never exceed it's rating because when one phase was peaking at the top of it's phase, the other was at the bottom of the wave.

    I am not explaining this very well, but I hope you get the idea.

    Now in the real world, in a small off grid cabin it seems to me that this wouldn't be an issue assuming that you have wired your building and your panel to account for this rule. A small number of branch circuits carrying small loads shouldn't be a problem, assuming that the neutrals are wired properly.

    I'm sure that some one will chime in with a better technical reason.

    Tony
  • BB.BB. Posts: 25,158Super Moderators admin
    Re: inverter to AC breaker box (off-grid)

    There are several issues.
    1. Inverter need to support a grounded neutral if you are following code--most MSW do not, many (most) TSW do.
    2. If you need 240 VAC--those appliances will see zero volts if the Black and Red hot leads are tied together (not a problem if all 120 VAC loads).
    3. You need to understand the wiring of your system... If you have a typical Black/Red/Neutral setup on a split phase 120/240 VAC branch circuit using 14 AWG wiring... Each wire can carry 15 amps (typical NEC). Black to White 15 amps (120 VAC). Red to White 15 amps (15 amps). And Black to Red 15 amps (240 VAC)
    When the Black and Red are split phase, the Black + Red current adds to Zero amps on the White wire (the split phase part--i.e., center tap of a transformer).

    If, your Black/Red are both the same 120 VAC phase with White... You could put 15 amps down Black and 15 amps down Red, and the White will carry back 30 amps and overheat.

    The breaker/fuse is only on the Black/Red branch wires. The White/Neutral does not have any fuses/breaker and can be overheated if connected to an inverter that can output, for example, 30 amps.

    However, if your inverter can only output 15 amps at 120 VAC total (or you use 1x 15 amp breaker to power both BL/RD wires instead of 2x 15 amp breakers, one for each BL and RD wire)--you will be perfectly safe.

    -Bill

    PS: You could also use two White Wires (Black+White #1 / Red+White #2) and be OK too... If you had a really big inverter with a really small breaker box--I guess you could overheat the neutral bus bar with the additive currents--normally the neutral bus bar would be designed to handle one leg's worth of current maximum).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭
    Re: inverter to AC breaker box (off-grid)

    The only reason the neutral will potentially carry more current is because the two independent inverters are not lock phased to be 180 degrees out of phase.

    In reality all neutrals to all outlets are brought back to the main breaker box neutral bus bar so the only place where more neutral current could occur is in the boxes neutral bus bar. Not much of an issue.

    In a normal grid fed box, the neutral line going back to the pole will not carry the sum of all the 120 v loads since some of them on either side of the neutral (L1,L2) will cancel their current contributions on the neutral cable back to the pole.

    Not much relevance to two inverters tied to L1 and L2 in a breaker box.

    Just make sure you don't have any 240 v loads unless the inverters are phase locked and inverted, like two stacked Trace SW series stacked inverters, and the inverters are neutral groundable.
  • BB.BB. Posts: 25,158Super Moderators admin
    Re: inverter to AC breaker box (off-grid)

    This was asked about 1x 600 watt inverter--I believe...

    So, L1/L2 tied to an inverter, with a common neutral, that is less than 1,800 watt output with 14 AWG wire (15-20 amp rated) is fine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bobdogbobdog Posts: 191Solar Expert ✭✭✭✭✭
    Re: inverter to AC breaker box (off-grid)
    BB. wrote: »
    This was asked about 1x 600 watt inverter--I believe...

    So, L1/L2 tied to an inverter, with a common neutral, that is less than 1,800 watt output with 14 AWG wire (15-20 amp rated) is fine.

    -Bill

    All very good info. I've paid so much attention to DC over the last year that I haven't really done my home work on AC. I just assumed I would take the 3 wires from a plugged in "cord" on the MSW cheap inverter and split the black to the buss bar on one side, the neutral to the ground and the ground to the ground. And then run my AC circuits (power accounted for) throughout the cabin. Then when I get a 2nd TSW inverter I would do the same except to the other buss.

    Now I'm not sure I can do that. I'm not sure about the phase issue and don't want to "blow up" my inverters let alone burn down the house.

    Is there a basic AC book that pertains to inverter power?

    And now I have to think about "wiring" in the generator too to charge batteries, run pump, etc.

    I got a lot of HW to do.:blush:
  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭
    Re: inverter to AC breaker box (off-grid)

    You won't have a problem with current carrying capability on the neutral.

    Your biggest potential issue is whether the Samlex MSW inverter you have is neutral plug side (the wider prong blade) groundable.

    Most MSW inverters have an H-bridge output with no isolation on the HV DC boost ground to battery ground. This allows some of the electronics on the AC H-bridge driver side to be run from the battery. A cheaper approach then having an separate, isolated secondary side generated low voltage DC source to run the H-bridge MOSFET's gates.

    The result is when you ground the neutral there will be an AC voltage to ground on the battery terminals. You will get a shock if you touch negative terminal of battery when standing on the ground. If you also ground the negative terminal of battery the inverter fuse will blow or inverter will blow out.
  • BB.BB. Posts: 25,158Super Moderators admin
    Re: inverter to AC breaker box (off-grid)

    I agree with RCinFL,
    bobdog wrote: »
    13. How can DC-AC inverters be connected to multi-wire branch circuits?

    Do not directly connect the hot side of the inverter to the two hot legs of the 120 / 240 VAC electrical breaker panel / load centre where multi-wire ( common neutral ) branch circuit wiring method is used for distribution of AC power. This may lead to overloading / overheating of the neutral conductor and is a risk of fire. A split phase transformer (isolated or auto-transformer ) of suitable wattage rating ( 25 % more than the wattage rating of the inverter ) with primary of 120 VAC and secondary of 120 / 240 VAC ( Two 120 VAC split phases 180 degrees apart) should be used. The hot and neutral of the 120 VAC output of the inverter should be fed to the primary of this transformer and the 2 hot outputs ( 120 VAC split phases ) and the neutral from the secondary of this transformer should be connected to the electrical breaker panel / load centre.

    Really need to know the exact model number of the inverter (and, if handy, a link to the manual).

    From the above, it appears that the inverter output is isolated and/or safe to ground reference (the AC neutral) because the warning talks about "Neutral" connections and overheating--and no warnings at all about grounding issues.

    However, because this just an excerpt of the manual--we don't know what other warnings there may be...

    Floating the "neutral" (not ground referencing the AC neutral) output of an inverter in a small cabin electrical system should not be a problem (even if the inverter supports a grounded neutral).

    The bigger issue is if you use a "standard" breaker panel--the neutral connection is not a floating bus bar--which means that the box, as supplied, is not safe to use with a "floating neutral" as the metal of the box can become energized as one leg of the inverter.

    So--a person ether needs to make up their own isolated neutral connection, or determine if the inverter supports a ground neutral or not.

    Unfortunately, equipment manufacturers are not always clear if grounded neutrals are allowed or not (even good companies like Honda and their very nice eu family gensets do not clearly sate if they support grounded neutrals).

    If you don't know for sure if an inverter supports a grounded neutral + grounded battery terminal--don't do it... Lots of sparks and smoke are possible.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭
    Re: inverter to AC breaker box (off-grid)

    I think most of the new breaker boxes have insulated neutral bus bar.

    This is required in a normal auxilary box setup to meet code of single ground bonding point back at the main breaker panel. The floating neutral in auxilary box is white wired over to neutral bus bar in main box which has the single point ground in main box case.
  • BB.BB. Posts: 25,158Super Moderators admin
    Re: inverter to AC breaker box (off-grid)

    Shows how long I have been inside one of those. :blush:

    Are the insulated neutral bus connections insulated to the normal 600 VAC as the rest of the box's hot leads will be?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭
    Re: inverter to AC breaker box (off-grid)

    I don't know the voltage isolation spec but the GE boxes I use have a half inch plastic base the whole length of bus bar which the neutral bar clips into. Some have two plastic standoff posts at either end of the neutral bus bar.

    There is a a provision for ground bonding at the end of the bus bar with a lug provided attached to the metal box.
  • BB.BB. Posts: 25,158Super Moderators admin
    Re: inverter to AC breaker box (off-grid)

    Sounds like the neutral block is properly isolated for MSW/Floating Neutral Inverter installation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭
    Re: inverter to AC breaker box (off-grid)

    Yes, but can you be sure that anything that is plugged in at any outlet is neutral isolated from ground ??
  • tallgirltallgirl Posts: 413Solar Expert ✭✭✭✭✭✭
    Re: inverter to AC breaker box (off-grid)
    RCinFLA wrote: »
    I don't know the voltage isolation spec but the GE boxes I use have a half inch plastic base the whole length of bus bar which the neutral bar clips into. Some have two plastic standoff posts are either end of the neutral bus bar.

    There is a a provision for ground bonding at the end of the bus bar with a lug provided attached to the metal box.

    There's typically one or two threaded holes in the neutral buss that can be used to bond the neutral buss bar to the box, with the expectation that the box itself is then grounded, making the neutral-to-ground connection at that point. Because systems must only have neutral and ground bonded at the service entrance, that connection is typically not made and you have to find the bonding screw and install it yourself.
  • dwhdwh Posts: 1,341Solar Expert ✭✭✭
    Re: inverter to AC breaker box (off-grid)

    The other way it's commonly done is with a copper strap - 1 end screwed to the box and the other end crimped/squished to make it wire-like. You just bend it up, stick into one of the wire holes in the bus bar and tighten down the screw if you need to bond neutral.
  • BB.BB. Posts: 25,158Super Moderators admin
    Re: inverter to AC breaker box (off-grid)
    RCinFLA wrote: »
    Yes, but can you be sure that anything that is plugged in at any outlet is neutral isolated from ground ??

    I cannot remember any application where Neutral and Ground are bonded at the outlet or in a plug-in device...

    The only exception being the RF Bypass caps that some devices have across Lines and Ground... (less than 2.5 mAmps or so of current--IIRC for a standard 120 VAC 15 amp max device).

    If you have a power strip--you might find the MOV's (across all three too for surge protection).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bobdogbobdog Posts: 191Solar Expert ✭✭✭✭✭
    Re: inverter to AC breaker box (off-grid)

    "The internal wiring of the Samlex prevents such an installation IF the neutral and ground are bonded in your AC breaker box. It will ruin the inverter if your neutral and ground are bonded."

    This was in response to my questions as to why you cannot connect the Samlex to an AC box. So, now I wonder if you can do that with any but the most expensive inverters?

    As far as the recent posts, I'm lost. My ignorance of the methods spoken of and the language inhibits me from following the thread. But, keep it coming. I'll figure it out eventually.:confused:
  • bobdogbobdog Posts: 191Solar Expert ✭✭✭✭✭
    Re: inverter to AC breaker box (off-grid)
    tallgirl wrote: »
    There's typically one or two threaded holes in the neutral buss that can be used to bond the neutral buss bar to the box, with the expectation that the box itself is then grounded, making the neutral-to-ground connection at that point. Because systems must only have neutral and ground bonded at the service entrance, that connection is typically not made and you have to find the bonding screw and install it yourself.

    So, as I understand this, the neutral IS bonded to the ground (just at the box), even with a new isolated neutral buss bar. So in that case what's the point of having an"isolated" (ergo insulated) neutral buss bar? As a friend says, "What does it buy you?"

    So we're back to the neutral being grounded and the Samlex and other MSW/Cheap inverters not being able to be used?
  • BB.BB. Posts: 25,158Super Moderators admin
    Re: inverter to AC breaker box (off-grid)

    First, exactly what model of Samlex inverter are you asking about. We need to get the right manual and see what it says.

    Having an insulated/isolated neutral bus bar--The idea is that the ground+AC Neutral is electrically connected (bonded) in one location.

    The idea of having a grounded neutral (as I understand it) -- is to help keep you safe if something goes wrong. If your home did not have one leg of the AC wiring grounded (remember, the most voltage you will see is 120 VAC to ground in North American Home wiring)--The outside wiring could have a 12,000 volt wire on the power pole fall and hit the 120/240 VAC wires into your home. The ground connection will help keep that 12,000 volts from entering your home.

    For an AC inverter in your cabin/off grid home--you will not have those types of issues. About the only high voltage danger is from lightning strikes. And--if a strike hits your DC/AC wiring--a grounded neutral, or not, is going to be the least of your problems.

    Neutral bonding theory; If you have, for example, the neutral+ground tied at the main panel, and at the panel in the garage--there are two major issues.
    1. You end up with a parallel connection of the white/neutral wire + the green/safety ground wire and each carries a part of the load. The green/safety wire is not supposed to part of the normal current carrying circuit, but is to only carry current in an "emergency". Having unintentional current paths becomes a problem too when you don't know if the current flows in the wrong wire and may exceed its current carrying capacity (and overheats). For example, if you have a white wire and metal conduit--the conduit will carry current too (not made to carry load current and can cause joints to fail, etc.).
    2. If there is a lightning strike nearby--the ground rod(s) can pickup the electrical energy in the soil and inject it into your wiring/appliances and cause problems.
    Different inverters have different requirements. We (other posters) don't know if you are using a TSW (True Sine Wave) or MSW (Modified Square/Sine Wave) inverter (Samlex does make both types).

    MSW inverters typically electrically connect the DC Battery Side to the AC output through its internal electronic switches. If the battery is grounded, and the AC "Neutral" is grounded--it creates a dead short across the battery which will destroy the inverter.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • n3qikn3qik Posts: 741Solar Expert ✭✭
    Re: inverter to AC breaker box (off-grid)

    Look on the Samlex web site. The only 600 watt inverter was this:

    PST-60S-12A 600 Watt Pure Sine Wave Inverter, 12VDC-120VAC

    And the manual stated this:
    CAUTION! : For the 120 VAC, 60 Hz NEMA 5-15R receptacles used in this inverter, the current
    carrying conductor connected to the longer rectangular slot is isolated from the metal chassis of the
    inverter. Hence, when the metal chassis of the inverter is connected to the earth ground, the longer
    rectangular slot is not grounded to the earth ground. The longer rectangular slot is, therefore, not a
    “neutral”. Do not touch this slot as it will be at an elevated voltage with respect to the metal chassis
    / earth ground and may produce an electrical shock when touched.

    If this is the correct inverter. Then looks like the ground will NOT be tied to the neutral at the box.
  • BB.BB. Posts: 25,158Super Moderators admin
    Re: inverter to AC breaker box (off-grid)
    n3qik wrote: »
    If this is the correct inverter. Then looks like the ground will NOT be tied to the neutral at the box.

    [opps--read the post wrong]

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • tallgirltallgirl Posts: 413Solar Expert ✭✭✭✭✭✭
    Re: inverter to AC breaker box (off-grid)
    bobdog wrote: »
    So, as I understand this, the neutral IS bonded to the ground (just at the box), even with a new isolated neutral buss bar. So in that case what's the point of having an"isolated" (ergo insulated) neutral buss bar? As a friend says, "What does it buy you?"

    So we're back to the neutral being grounded and the Samlex and other MSW/Cheap inverters not being able to be used?

    Some of "Why?" has been explained elsewhere. I'm going to explain more "Why?"

    In a typical dwelling there are multiple panels. I have 3 or 4 or maybe even 5. Sometimes I lose count.

    The only place "Neutral" and "Ground" MAY be connected are at the service entrance. There are some other complicated rules, but I'm going to ignore all of them because they aren't relevant to this discussion.

    Incorrect connecting "Neutral" and "Ground" is a bad idea -- see the discussions below.

    Therefore, MOST panels will not have "Neutral" and "Ground" connected in that panel, and the insulated neutral bar is working as expected -- it's isolated from the system ground.

    That covers why neutral buss bars are insulated from ground by default.

    With inverters, whether or not there even is a "Neutral" is a subject of some discussion. Most MSW inverters don't have a real neutral. They produce 60VAC RMS (though RMS is probably not even right -- these are just stepped square waves) split phase power -- two 60VAC wave forms 180 degrees out of phase, for a total peak-to-peak of 120VAC. Thus, instead of "Neutral" having 0VAC +/- voltage drop, relative to ground, "Neutral" has 60VAC +/- relative to ground. Tying that to ground will probably result in sparks and the smoke escaping from the inverter.
  • n3qikn3qik Posts: 741Solar Expert ✭✭
    Re: inverter to AC breaker box (off-grid)
    BB. wrote: »
    Because the "Neutral" is already connected to "ground" inside the inverter... So you do not want/need to connect your neutral elsewhere.

    The manual should give you a diagram of how to ground the metal chassis of the inverter and the battery bank.

    -Bill

    One the model I posted, the neutral is floating. This is why there is a waning about the longer prong (neutral) being a electrocution hazard.

    tallgirl has stated why, as in respect to the inverter not to bond the neutral and ground toghther.
  • BB.BB. Posts: 25,158Super Moderators admin
    Re: inverter to AC breaker box (off-grid)

    n3qik,

    Opps... You are correct--I missed the "not" in there.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwhdwh Posts: 1,341Solar Expert ✭✭✭
    Re: inverter to AC breaker box (off-grid)
    bobdog wrote: »
    So, as I understand this, the neutral IS bonded to the ground (just at the box), even with a new isolated neutral buss bar. So in that case what's the point of having an"isolated" (ergo insulated) neutral buss bar? As a friend says, "What does it buy you?"

    Neutral must be bonded to ground, but ONLY at one point - the main "service entrance" panel.

    Sub-panels tapped off the main panel must NOT have their neutral bonded to ground.

    Due to this, almost all panels nowadays come from the factory with the neutral bus isolated - BUT, provision is made to allow the installer to bond that neutral bus to ground if required (if the panel is used as the "main" panel).

    The two main ways this is done, is to either;

    A) At the factory they drill clean through the neutral bus bar, and the box, and then include a couple of long screws. Then, if need be, the installer can run the screws through the bus bar and screw them into pre-drilled holes in the metal box.

    or

    B) At the factory they take a piece of flat copper strap and crimp one end so it's "wire-like". Then they screw the flat end of the strap to the box next to the neutral bus bar. If the installer then needs to bond neutral to ground, he (or she, TG) can simply bend it up and stick it into the neutral bus bar and tighten down a screw.


    For your off-grid application, you would install the 120v AC system just as though it were to be fed from the grid - i.e., you WOULD bond neutral to ground at the main panel.

    Which is apparently a problem for the inverter you have, since it is not designed to be attached to such a system - it has neutral and ground bonded inside of it.

    Some generators have this same problem, though some are designed so that you can "lift" (disconnect) the neutral to ground connection and thus make them correct for connection to a properly grounded 120v system.


    Okay...now...for your situation - little off-grid cabin. I tend to approach such things are roughly equivalent to an RV.

    You first asked about tying the inverter to both "legs" or "phases" of your panel. Well...if there are NO 220v circuits in your panel and NO 220v feed from a generator or grid - then there really isn't any problem with feeding both hot bus bars from one single-phase 120v source. Just tie the two bus bars into one and call the whole thing a "120v panel".

    No problem - other than, of course, the potential (pun intended) problem of overloading your inverter. But that's not a safety issue.

    The other issue is grounding/bonding.

    Now, an RV is not grounded - unless connected to shore power. And your inverter would be perfectly OK to use in an RV.

    So, (insert rapidly spoken legal disclaimers about don't do this at home and do as I say, not as I do and so on and so forth, ad infinitum) why not just treat your cabin as an RV for wiring purposes and NOT bond neutral to ground in the main panel? I.e., allow the inverter to serve as the neutral to ground bond - since it IS already built for that.

    Just bond the chassis of the inverter to ground and leave the neutral bus in the panel isolated. There is still a neutral to ground bonding, it's just in the inverter instead of in the panel - which should be fine, since the inverter is the source of the power anyway.


    If you were in an RV and the 120v source was a generator - the neutral to ground bonding would be done in the generator.
  • bobdogbobdog Posts: 191Solar Expert ✭✭✭✭✭
    Re: inverter to AC breaker box (off-grid)

    Here is link to the manufacturers website: (note all the inverters are called pure sine wave)

    http://www.samlexamerica.com/pure_sine_wave_inverters.htm

    The Cotek or 'S' series and the "PST" versions are what I was referring to. My system is 12 volt and I was looking at the 300 models.

    This brand is sold here at our hosts' website (pst version) and others such as backwoods solar (s-version), etc. The FAQ part of the manufacturers website

    ( http://www.samlexamerica.com/customer_support/faq.htm )

    has a good general information section (see #13) and a neutral/grounding section that has good information as well. What is great is that I can go back and reread the information provided by them after reading the responses here, and better understand what the heck they are talking about.

    I'm glad I asked the original and subsequent questions since all the responses I've received during the discussion have been very enlightening and helpful.

    The bottom line is that I read one thing and then was told not to do it (i.e. bond neutral to ground). After reading the discussion and re-reading , I think I understand my situation better, the idea and theory of neutral/grounding and how it all applies to a cabin (RV). In short I wish I could afford an expensive 1000 watt pure sign wave inverter and other top of the line things. However, I can't and so look at the down line items that fall within my needs and my budget. Samlex seemed to do that and I'm glad that NAWS chooses to carry such items.

    My confusion lies when I here/read one thing and then also the opposite. That's why I ask you good folks for advice. As always, I thank you for your incite and patience.

    BTW - I would like to here from a NAWS rep on this since they do sell them and just see what their thoughts on the matter are....
  • dwhdwh Posts: 1,341Solar Expert ✭✭✭
    Re: inverter to AC breaker box (off-grid)

    Okay, with those inverters you definitely do NOT bond neutral to ground - and it's not bonded to ground in the inverter either. You do however bond the chassis of the inverter to ground and you would also bond the chassis of the electrical panel to ground.

    I.e., connect the metal box of the panel to the ground rod, and also connect the chassis of the inverter to the ground rod.

    But DO NOT bond neutral to ground in the panel. Make sure your panel has an isolated neutral - i.e., the neutral bus bar sits on plastic mounts so it doesn't touch the metal box.

    Also, when you stick neutral wires through the holes in the bus bar - DO NOT make them overly long and let them touch the box.


    The REASON why you don't bond neutral to ground with that inverter is because the neutral IS NOT neutral - it's hot! If you bonded hot to ground it would just short the inverter out.

    From the manual:

    http://www.samlexamerica.com/customer_support/pdf/Manuals/PST-100S-12A_24A_Manual_Dec2005.pdf

    "CAUTION! : In these NEMA 5-15R receptacles, the current carrying conductor connected to the longer rectangular slot is isolated from the metal chassis of the inverter. Hence, when the metal chassis of the inverter is connected to the earth ground, the longer rectangular slot is not grounded to the earth ground. The longer rectangular slot is, therefore, not a “neutral”. Do not touch this slot as it will be at an elevated voltage with respect to the metal chassis / earth ground and may produce an electrical shock when touched."

    Due to that, I WOULD NOT use that inverter hooked to an electrical panel UNLESS there was a GFCI between the inverter and the panel. Some of their inverters do have a GFCI option. For your application I would ABSOLUTELY get that.

    Without GFCI I would say, "definately do NOT feed your panel with that inverter".


    Having said that - they do say in the manual:

    "If an electrical breaker panel / load center is fed from an inverter and this panel is also required to be powered from additional alternate AC sources, the AC power from all the AC sources like the utility / generator / inverter should first be fed to a manual selector switch and the output of the selector switch should be connected to the electrical breaker panel / load center."


    Okay...that's to prevent paralleling (blowing up your inverter by backfeeding it power from a grid or generator), but it IS a tacit approval of connecting the inverter to a panel.


    They also say:

    "Do not directly connect the hot side of the 120 VAC of the inverter to the two hot legs of the 120 / 240 VAC electrical breaker panel / load centre where multi-wire (common neutral) branch circuit wiring method is used for distribution of AC power. This may lead to overloading / overheating of the neutral conductor and is a risk of fire."

    What they are referring to is what is called a "3-wire circuit". It's two hots (coming off of two breakers) sharing a single neutral. Okay, so don't make any 3-wire circuits - use a dedicated neutral for every hot...problem solved.


    So...

    * NOT ALLOWED: 220v feeding into the panel from either grid or generator.
    * NOT ALLOWED: 220v branch circuits.
    * NOT ALLOWED: 3-wire branch circuits.
    * GFCI REQUIRED. (Buy an inverter with the GFCI option or install a GFCI between the inverter and the panel.)

    Step 1.
    Make sure there are no 220v branch circuits or 3-wire branch circuits.

    Step 2.
    Tie the two hot bus bars together to make the panel a 120v panel.

    Step 3.
    Ground the chassis of the panel but DO NOT bond neutral to ground.

    Step 4.
    Ground the chassis of the inverter.

    Step 5.
    Feed the inverter AC output into a GFCI and then feed from the GFCI into the panel.

    Step 6.
    Kick the tires and light the fires.
  • bobdogbobdog Posts: 191Solar Expert ✭✭✭✭✭
    Re: inverter to AC breaker box (off-grid)

    Excellent analysis of the issue DWH. I appreciate the work you have put in, especially reading and then giving advice. I read the same things, but your interpretation makes it much more clear.

    So, I hope I have it right.
    1) jump the two hot (main) bus bars together to make one hot, 120v panel
    2) run the one "hot" wire from a circuit (in my case the black wire) into the breaker, "plug" the breaker into the buss (panel)
    3) the white or neutral wire of the circuit goes to an isolated neutral buss bar
    4) the green to ground

    AND from the inverter:
    1) the black wire from my 'Plug' goes to the hot, main buss
    2) the white goes to the isolated neutral
    3) the green (or ground plug wire) goes to the ground buss

    Finally, ground the panel, but NOT the neutral bar

    And either get an inverter with a GFCI or put one between the inverter and the panel


    If I had 2 inverters, couldn't I simply use one side of the panel for this inverter/circuits (not jump the 2 sides) and the other side for the other inverter/circuits? Or would I run into neutral buss issues? (EDIT: just read the 3-way circuit line and you said for every hot make a dedicated neutral. Does that mean for every HOT breaker I have a neutral bar? I'm sure I'm mis-understanding.)

    Given all of that, I assume not all inverters, let alone pure sine wave inverters require this setup? And doesn't this leave me with no place to run power "back" to the source as if I had a 'real' neutral? Maybe this is NOT the inverter for my cabin then.
  • dwhdwh Posts: 1,341Solar Expert ✭✭✭
    Re: inverter to AC breaker box (off-grid)
    bobdog wrote: »
    Excellent analysis of the issue DWH. I appreciate the work you have put in, especially reading and then giving advice. I read the same things, but your interpretation makes it much more clear.

    When I was a boy I read something in a "Mel Bay" music book which I have never forgotten; "To learn, teach."

    I'm here to learn just like eveyone else so doing what I do helps me as well. I'm mercenary, not altruistic. :D

    So, I hope I have it right.
    1) jump the two hot (main) bus bars together to make one hot, 120v panel
    2) run the one "hot" wire from a circuit (in my case the black wire) into the breaker, "plug" the breaker into the buss (panel)
    3) the white or neutral wire of the circuit goes to an isolated neutral buss bar
    4) the green to ground

    AND from the inverter:
    1) the black wire from my 'Plug' goes to the hot, main buss
    2) the white goes to the isolated neutral
    3) the green (or ground plug wire) goes to the ground buss

    Finally, ground the panel, but NOT the neutral bar

    And either get an inverter with a GFCI or put one between the inverter and the panel

    Yup.

    Make sure you have one neutral (white) per hot (black) - no sharing neutrals.

    Also, again, be careful when stripping the neutrals and sticking them in the neutral bus bar. The bus bar will likely be very close to the side of the box - maybe 1/2" or less gap. Keep the stripped end of the neutrals just long enough to penetrate the bus bar, but not long enough to touch the box.


    If I had 2 inverters, couldn't I simply use one side of the panel for this inverter/circuits (not jump the 2 sides) and the other side for the other inverter/circuits? Or would I run into neutral buss issues?

    To rig that, you would need to have two neutral bus bars isolated not only from ground, but also from each other. You would also have to make CERTAIN, that you didn't get any mixing. I.e., If a hot is on "Inverter A" you better make sure that the neutral doesn't get stuck into the neutral bus bar for "Inverter B".

    But that's just hypothetical since by doing something like that you are starting to get into realm of "dodgy and possibly dangerous" because even though you know how the system is rigged, the next guy won't unless you make extraordinary effort to label everything with WARNINGs.

    (Actually, this discussion is ALREADY bordering the realm of dodgy and possibly dangerous. I have no doubt that some of the engineers here (there are many) are cringing and just itching to tell me to shut up. And so, I must insert the next paragraph...)

    Better to have two small panels each fed by their own inverter or even better to buy a bigger inverter so you don't need two to begin with. I DO NOT RECOMMEND FEEDING ONE PANEL WITH TWO SEPARATE INVERTERS UNLESS THE INVERTERS ARE DESIGNED TO BE PARALLELED WITH EACH OTHER. In fact, I strongly advise against it.

    (EDIT: just read the 3-way circuit line and you said for every hot make a dedicated neutral. Does that mean for every HOT breaker I have a neutral bar? I'm sure I'm mis-understanding.)

    No, it means for every hot wire you have to have a neutral wire back to the bus bar.

    For example, you can buy "3-wire" romex with one white, one black and one red (and one bare ground, but it doesn't count as a "wire"). You can wire it so that each hot (red and black) goes into a separate breaker and thus the two circuits (say one for upstairs lights and one for downstairs lights) share the same neutral (return path).

    That is a perfectly legit, legal and common thing to do (under certain circumstances - it is forbidden for other uses). However, it must not be done with those particular Samlex inverters.

    If you are wiring things up yourself - use only "2-wire" romex (black, white and bare ground). That way no matter what, you will have a neutral for every hot.

    Given all of that, I assume not all inverters, let alone pure sine wave inverters require this setup? And doesn't this leave me with no place to run power "back" to the source as if I had a 'real' neutral? Maybe this is NOT the inverter for my cabin then.


    I'm not sure what you mean by that "run power back to the source" statement.


    As for the differences in inverters, I would have to defer to the engineers to answer that. My understanding is limited. From what I understand, there are:

    * MSW
    Modified Square Wave - sometimes referred to as Modified Sine Wave which is usually marketroid doublespeak, but sometimes means that the square wave has so many steps it is really VERY close to a sine wave.

    * PSW
    Pure Sine Wave - which seems to me to usually be a highly stepped square wave which comes very close to being a sine. I suppose if you zoom out then it really is a sine.

    * The Good Stuff
    I have no doubt there are some really nice and expensive inverters that really do put out an absolutely true sine wave. Some of these put out 220v split-phase and are designed to feed electrical panels.


    I have a feeling that when dealing with low cost inverters, there probably isn't all that much difference. How many have a "neutral" that is actually another hot? Dunno. Probably a lot of them.


    Quite often here in the forums we see a conflict between "the right way" and "the cheap way". You are certainly not the first to try to setup an off-grid power rig "on a budget" (hell, I'm a cheap bast**d myself).

    Let me ask you this: WHY do you keep wandering off into the dual inverter train of thought?

    Is it because you have a need to supply 220v to something?

    Or is it just because you want more wattage available? Like maybe you'd like to start out supplying the panel with 1000w today and maybe add another 1000w later? Or maybe you're thinking that two lowbuck 1000w inverters will cost less than a 2000w bigboy?
  • bobdogbobdog Posts: 191Solar Expert ✭✭✭✭✭
    Re: inverter to AC breaker box (off-grid)
    dwh wrote: »
    Let me ask you this: WHY do you keep wandering off into the dual inverter train of thought?

    Is it because you have a need to supply 220v to something?

    Or is it just because you want more wattage available? Like maybe you'd like to start out supplying the panel with 1000w today and maybe add another 1000w later? Or maybe you're thinking that two lowbuck 1000w inverters will cost less than a 2000w bigboy?


    I have a cheapizoid 750 watt MSW inverter. I can use it for lights and other "non" electronic equipment. I would also like to buy a TSW (or PSW) inverter for the electronic stuff and possibly other things down the road. I will eventually get rid of the MSW, but due to being budget constrained it is there for the time being.

    My question on using a single panel, was simply so I wouldn't have to have 2 panels. I figured your answer was the proper one (safe one!) and will just put in 2 panels. Down the road if i can afford one really nice TSW big boy, then I can do something else with the 2nd panel.

    BTW - I still haven't heard from our host site on their take on the inverters they sell (ergo Samlex)
  • BB.BB. Posts: 25,158Super Moderators admin
    Re: inverter to AC breaker box (off-grid)

    Just an FYI--NAWS/Windsun does not monitor this site for business questions/issues. The forum is a wholly independent operation intended as a community for people to help each other out.

    If you have question for NAWS--please contact them directly. They will be more than happy to help.,

    About Northern Arizona Wind & Sun

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