Converted Bus/RV Solar Grounding/Bonding

divideoverflowdivideoverflow Registered Users Posts: 7 ✭✭
First of all, thank you to Bill (BB.)! On what seems to be the whole of the internet, you are one of two or three people that seem to understand anything about solar grounding as it relates to the NEC, GFDs, and RVs. I'm an electrical engineer (but on the high voltage 69kV+ side), and I felt overwhelmed as I dove into everything going on with my solar design grounding / bonding plans. Your posts have helped tremendously.

Sorry everyone in advance for the long post. It is a struggle to get to the questions without the background so far.

Here is where I'm at, and could use some confirmation or suggestions.
Part 1, DC:
48V battery bank with 4000 watt split phase schneider conext inverter, charge controller, and various switchgear. I'm running a 240v mini split air conditioner so I always need both AC legs hot. 2600 watts of solar made up of four 80V parallel strings.

Charge controller uses the "1 amp fuse connecting battery negative to chassis ground" for it's PV-GFP. I'm aware if this fuse blows than the DC system is floating. I prefer not to have a hard ground from my 48v system to the bus chassis ground, as I worry about my 12V bus electronics (very expensive ECUs and transmission controllers) should I have a major battery fault. Am I over reacting on not wanting them bonded? 

My plan is to have a 2-pole DC breaker for positive and negative PV leads between my combiner box and my charge controller. If the 1 amp GFP fuse blows, it is supposed to shut down the whole system (charge controller, inverter, etc), but doesn't trip any physical breakers. I doubt the PV will provide enough current to pop the 80 amp 2-pole breaker, so it would be more of a manual disconnect. I have individual breakers for each PV string in the combiner box, but only on the positive leads. My wires on the roof will be in non conductive conduit from the panels to the roof entry.

On the battery side (8-12v 190ah AGM Telecom batteries in two strings of four series batteries), I'm putting 400 amp fuses on my positive and negative leads (in each string, as well as after the bus bar where they combine). The battery banks can put out 350 amps for 15 minutes per their rating, and have a short circuit current of 3500 amps, so I felt like 400 amps was a safe number to use. Also, all wire connections are 4/0 on the batteries, and that seems to be the most common fuse size for that wire. The DC switchgear has a 300 amp main breaker to disconnect the batteries, but only has a 1-pole positive breaker. Since DC breakers are directional, it should really only blow for load side faults as it is. Does that seem sufficient for a floating ground bank? I didn't want to go small on the fuses and risk blowing them if I'm using the welder or a hair dryer on startup.

Anything I could do better? I could remove the charge controller gfd fuse and run a separate GFCI device that automatically drops the PV circuits when a ground fault is detected, but that requires a real bond between my DC negative and the chassis.

Part 2: AC Neutral hell.
Schneider hasn't responded to my emails yet regarding how the inverter handles the neutral exactly, but here is what I know:
Inverter defaults to no neutral to ground connection, and expects it from the utility panel. But they give instructions to create the neutral to ground bond at the inverter if desired.

Per schnider FAQ: 
"CSW neutral switches internally to energize transformer for split-phase when inverting, and when supplying 120VAC to L1-N. When operating as charger for 120/240VAC source, the internal neutral relay disconnects from transformer so it operates as stricly 240V charger.
Resolution :  
Be aware CSW has common neutral internally."

So it seems like when AC source is detected, the internal neutral disconnects and let's the utility neutral/ground bond pass through. When there is no AC detected, the inverter gives the neutral reference. 

Ok, so we have the following usage scenarios:
1.Solar and batteries only. Inverter creates L1 and L2 phases, as well as the neutral reference. Currently neutral would be floating in this scenario.

2. Shore power. Neutral is bonded to ground on the utility side. I have separate plugs for 30 amp and 50 amp connections, they are separated on the hot legs via a manual transfer switch. Neutral is not on the switch, so if I plug in shore power, neutral is grounded. When I unplug it, it is floating. 

3. Generator plugged into 30amp recepticle. Currently the generator has no g-n bond, but I could add one.

So the big question: I assume I need to work out a neutral to ground bond to my chassis ground when I'm disconnected from shore power or the generator? My neutral is completely isolated, everything is in conduit. All enclosures and outlets have their ground wires terminate back at the AC switchgear (and Inverter). It seems like a lot of solar installs in RVs end up with floated neutrals... But I am running GFCI breakers in the kitchen and bathroom, I'm assuming they will pop when the chassis ground and neutral diverge?

It sounds like I need yet another transfer switch to choose between my AC inputs (the 50 amp and 30 amp recepticles) and solar only. My inverter 100% does not do neutral to ground bond switching (so says the manual). It is expecting a single use case scenario.

Would making a "ground to neutral bond plug" that just sits in my 50 amp recepticle do the trick? I would have to remove it before plugging in 50 amp shore power (so it wouldn't impact that bond point), and I could leave my small generator floating (it only hooks to the 30 amp recepticle)

Is there a safe way to run a floating neutral? I will run computer equipment off of the inverter, so I'm also concerned about impacts to sensitive electronics.

Thanks for any advice anyone may have! 
(In progress photo)


Comments

  • mike95490mike95490 Solar Expert Posts: 8,882 ✭✭✭✭✭
    One thing that stands out, is the " AGM Telecom Batteries".    Great if you got them at a very low cost, as they are designed for stationary Float service .   in Deep cycle service,  they won't last a long time.
    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 ,

  • divideoverflowdivideoverflow Registered Users Posts: 7 ✭✭
    I did get them at a good price ($120 each, never used). Based on their literature, I should get 1000 cycles or better out of them. I don't plan on exceeding 50% depth of discharge.

    Considering I got my whole bank for the price of a single battleborn, I'll be happy as long as they last a couple of years.


  • BB.BB. Super Moderators, Administrators Posts: 30,760 admin
    Welcome to the forum DOF,

    And thank you for the kind words... We try our best here.

    Let me try for some short and sweet answers, and we can go into details where needed.

    1) The DC Ground Fault system in the NEC... This was a quick and dirty protection plan intended to prevent Arc Faults... The reality, this cause other issues that were much more dangerous ("floating safety grounds" and "invertering" Hot vs Neutral legs--A huge no-no).

    Of course, I am making a personal statement here--What you do, is your choice. We have a thread and I wrote a white paper (in 2011--time flies when you are having fun):

    https://forum.solar-electric.com/discussion/9345/system-grounding

    My take on it is to do the standard connecting the DC negative bus to chassis/earth/safety ground (just like is done in vehicles, homes with AC neutral+safety ground bonding, etc.) and don't use the NEC DC GFI system.

    There are DC arc fault and Ground Fault Detection systems (some Midnite MPPT solar charge controllers have Arc Fault detection, MorningStar has a DC Ground Fault Box--But not the same as an AC GFI that can detect/trip on 0.010 or so Amps).

    The issue with vehicles is that there is lots of metal, and the "metal" will have highly variable electrical connectivity to "chassis ground" (rubber bushings for noise isolation, metal bushings and bearings in door hinges, springs, metal panels that have paint preventing good electrical grounding, new buses that use double stick tape for panels, etc.).

    You probably have to run (for example 6 AWG) ground cable from your DC negative bus to the chassis of your solar charge controller, AC inverter, etc., and tie that to the bus "chassis ground" (whatever that may be). What you want is a "short circuit" to chassis on any of those to go back to the battery negative bus and "trip" the breaker for that circuit.

    And you would do the same thing with your AC system (assuming PSW inverter, ground bonded Neutral). And carry a green wire ground from the main AC panel (and/or use metal conduit) to each outlet/etc. (don't think flex conduit is a "legal" ground path). And tie to water pipes (if metal), propane pipes, stove, etc.

    Of course, Neutral+Ground bonding is complicated subject in RVs... You have the N+G bond takes place in the shore power connection (RV park power). Or in the AC inverter in the RV. Or in the RV AC Genset... During the installation, you have to figure out where the RV N+G bonds are, remove some, and add a transfer switch that either "lifts" the RV N+G (when on shore power) and connects N+G when on RV Inverter and/or Genset (some inverters may include transfer switch and G+N transfer too). 

    If you are using GFI outlets or breakers (in your AC breaker panel), you don't "need" the green wire grounding everywhere. The GFI will trip even if there is ~0.010-0.025 amps of Hot to ground leakage current.

    And you would tie the AC greenwire safety ground to the DC Negative ground/chassis ground connection.

    AS I mentioned above, in vehicles, poor grounding is pretty common. Running dedicated ground cable(s) to all of your DC devices (that can short/fail) and not use the RV for grounding is a good solution. Also it is common to add bonding straps across the "poor connections like door hinges, rubber vibration insulation bushings, etc.). Aircraft do this, and folks running HF HAM radios in vehicles add ground bonding "everywhere" (hinges, between panels, frames, etc.)--This is to reduce background RF noise. In aircraft to protect hinges and hinge bearings from spot welding during lightning strikes.

    Running dedicated grounds cables and bonding "metal" can help protect your vehicle electronics--And avoid using the vehicle "metal"/wiring/etc. in the cockpit area for heavy DC power (don't install the inverter next to the instrument cluster without dedicated wiring/grounding back to your house system power)....

    I think I am wandering here... Stop before becomes more confusing.

    If you have a "solid" return to chassis ground bond (DC negative to ground chassis bonding, AC neutral to chassis ground, etc.), you do not need "pairs" of breakers on (for example) DC + and - connections. The + is "hot", and the - bus cannot go above ~0 volts because of Neutral/Return+Ground bonding. Using "pairs" of breaker is really only needed for "floating systems" (or using the NEC DC GFI funky ground bonding system with the 1 amp sense or the 1 am breaker tied to other breakers).

    I believe what "they" were after was if a fault blows the 1 amp detection fuse, then the device (typically solar charge controller) stops working (shuts down). Or with the 1 amp breaker paired with one or more large breakers (60 amp or more) tied to (for example) the solar panel wiring to the charge controller--Hopefully, the owner of the system notices the "equipment failure", and fixes the problem.

    But as you have seen, this is extremely hazardous (1 amp fuse/breaker between various "safety ground"--Something never allowed anywhere else).

    Doing "hard grounding" solves a lot of problems... And why I am no fan of the NEC DC GFI system. The NEC DC GFI was presented as a quick way to reduce the problems of Arc Faults--A real problem with solar+DC power systems--But the problems created address only a small part of the overall Arc Fault issues.

    I think you know and are aware of these issues. If you do the standard "return" (DC - Ground/AC Neutral) to chassis bonding, it will make, at least part of the problems, "go away" (using breaker on + DC lines, and on L-N-L AC systems, only use the standard LL double pole breakers (and single pole breakers on L power).

    Will continue in next post.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 30,760 admin
    The 12 volt @ 190 AH telecom batteries--Many telecom batteries are design for "float service"... And if they are deep cycle more than a "few times", they will begin to lose their capacity.

    AGM batteries are nice (no water levels to check, much cleaner)... But I would suggest, if you can justify, looking a 6 volt (or even 4 or 2 volt cells--Larger AH rated "batteries" means fewer parallel strings--And if flooded cells, fewer cells to check electrolyte levels on), I do not like lots of highly paralleled battery strings. 1 to 2 parallel strings is probably ideal... More than 3 parallel strings I would suggest avoiding (more cells, more connections that can fail). And it is easier to find battery problems with a simple volt meter. You can measure the voltage across each 6 volt (or 4 or 2 volt) battery and see that all the voltages are about equal (or not). With 4x 12 volt batteries in parallel, you can only measure 12 volts of the ground--Finding weak batteries/strings is not easy without disconnecting the batteries so you can measure individually).

    And, if you "hard ground" the 12 Volt Return (-) bus to chassis--Then you only need fuses on the + bus/cable connections. Putting fuses/breakers on "return" or negative wiring in ground reference system is never done... It would be like fusing the neutrals on 120/240 VAC split phase main panels.

    There is also some issue in how you wire your battery bank. This website does a nice job describing how you parallel connect your batteries so that they evenly charge/discharge/share current:

    http://www.smartgauge.co.uk/batt_con.html

    Look at the DC breakers... If they are polarity sensitive, design the system with the battery as the "source" for high current. I believe, at some point, new DC breakers were designed to not be polarity sensitive. Polarity sensitive breakers use (as I understand) magnets to "blow" the arc into the arc quench channel... If the over current is going the "wrong direction", the magnets blow the arc away from the arch quench channel (not a good thing).

    2) AC Neutral Hell...

    Yes--It is.

    One issue with figuring out where the Neutral+Ground bond take place is where any GFI breakers and/or outlets are installed. More or less, you need the N+G bond to be on the "source" side of the GFI protective device. Do that, all is well (and if you "float" the AC neutral on the source side, the GFI devices will work fine too).

    Where you get into trouble is if you N+G bond on the input and output side of the GFI. That will "unbalance" the L/N current flow (part of the flow on the safety ground). And this is will trip your GFI device.

    If you N+G bond in the RV, this will (or least should) trip the GFI breaker/outlet in shore power box.

    Similar with the RV genset... If AC generator has GFI outlets (or GFI breakers), any G+N bonding downstream of the genset will trip the GFI protection on the generator. So you are left with bypassing the GFI protection on the generator.

    From what I have seen (no expert), generally smaller gensets and AC inverters (say less than 3kWatt) seem to have floating AC neutrals... And larger gensets and AC inverters seem to default from the factory with the AC neutral to chassis ground.

    Can you post a link to the exact CSW unit you are using--I need to do a bit of reading to figure out what they intended.

    But, I believe you will have to figure out where your transfer switch(es) will be installed....

    From what you describe, the CSW operates in an RV friendly way.... No AC input, it provides the AC Neutral+Ground bonding. With AC input, it floats the AC neutral.

    When the source is Shore power--That is what you want. Neutral bonding is done on shore power.

    And, if you want to run a genset, if the genset is also Neutral+Ground bonded (to RV Chassis/your power center safety ground of AC, Battery, etc. grounding), that should work too.

    Ok, so we have the following usage scenarios:
    1.Solar and batteries only. Inverter creates L1 and L2 phases, as well as the neutral reference. Currently neutral would be floating in this scenario.

    Those two sentences seem to be in conflict. CSW on battery, "creates tee neutral reference" seems to be correct.

    2. Shore power. Neutral is bonded to ground on the utility side. I have separate plugs for 30 amp and 50 amp connections, they are separated on the hot legs via a manual transfer switch. Neutral is not on the switch, so if I plug in shore power, neutral is grounded. When I unplug it, it is floating. I think this is OK. What you want to avoid is creating a "suicide" plug (120/240 power to blades is "HOT"). Neutral should always be near zero volts. You are carrying safety ground/green wire from shore to RV too (just confirming)?

    3. Generator plugged into 30 amp receptacle. Currently the generator has no g-n bond, but I could add one. If I am understanding everything correctly--Yes, you should N+G bond at the genset frame/RV frame/to your "ground window" -- Term used in Telecom where all the ground meet.

    So the big question: I assume I need to work out a neutral to ground bond to my chassis ground when I'm disconnected from shore power or the generator? My neutral is completely isolated, everything is in conduit. All enclosures and outlets have their ground wires terminate back at the AC switchgear (and Inverter). It seems like a lot of solar installs in RVs end up with floated neutrals... But I am running GFCI breakers in the kitchen and bathroom, I'm assuming they will pop when the chassis ground and neutral diverge? Presently, only when you are on Genset Power do you have a floating neutral. GFI receptacles "don't care" about safety ground. A GFI works by wrapping a couple turns of wire (or equivalent) around the L&N conductors, making a current transformer. When L out and N return currents are equal, the CT measures zero differential amps and all is well. When L out and N back are not "identical" out and return currents on L&N, the non-zero (>0.015 amps or so), trips the GFI protection (cut L&N connection). Diverging Ground and Neutral voltage, by itself, does not trip the GFI.

    See next post...
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 30,760 admin
    It sounds like I need yet another transfer switch to choose between my AC inputs (the 50 amp and 30 amp receptacles) and solar only. My inverter 100% does not do neutral to ground bond switching (so says the manual). It is expecting a single use case scenario.

    Need to clarify here... 50 and 30 amp "receptacles" or "plugs"? Earlier you said you had a 30/50 receptacle transfer switch but here no transfer switch? Do you have separate 30 amp and 50 cords? I thought the normal solution was a 50 amp cord/plug from the RV, and use a 50 amp receptacle to 30 amp plug adapter cable...

    And the inverter, did provide Neutral bonding when running from Batteries. And floats the neutral when AC power in.

    Depending on the inverter--Some have AC1 and AC2... AC1 for Utiltiy power, and AC2 for genset power. Yours only has 1x AC input?

    If you have only AC in... You can get a simple relay that you have the output go to the Inverter AC input... And has two inputs, one to Shore Power, and a second to Genset power. For example, default to Utility Power in, and when Genset AC present, switch over to Genset power automatically (these relays are not very expensive).

    Would making a "ground to neutral bond plug" that just sits in my 50 amp receptacle do the trick? I would have to remove it before plugging in 50 amp shore power (so it wouldn't impact that bond point), and I could leave my small generator floating (it only hooks to the 30 amp receptacle)

    I need clarification here.... A "male plug" goes into a "female receptacle"... If you made a 50 Amp receptacle that did nothing but tie Neutral to Greenwire safety ground--Yes, that would be a way to get N+G Bonding... If the genset does not have GFI breakers/receptacles, that would work. If the genset does have GFI protection, it would trip the protection. And in either case, you would have floating Neutral if you forgot the N+G 50 Amp "Cap". It would be better to either G+N inside the genset, or in the plug/box that connects to the genset and make the G+N connection there (you would never have a "floating Neutral" if done this way).

    Is there a safe way to run a floating neutral? I will run computer equipment off of the inverter, so I'm also concerned about impacts to sensitive electronics.

    Running GFI protected circuits/outlets is certainly "safe" (as I understand, older homes that have only L+N wiring and no ground, GFI outlets are a "safe" conversion from 2 connection to 3 connection (grounded) outlets--Even if there is no safety ground wire present.

    Your first and best solution is to use PSW/TSW inverters (pure/true sine wave). MSW (modified square/sine wave) inverters can be hard or even cause earlier failures for some devices (compressors on refrigerators, power bricks and small transformers for electronics/laptops, etc.). It is difficult to tell which devices can have "issues" with MSW inverters... Many will work fine, some won't.

    GFI protection for use near sinks, outside, etc. is there to help prevent electrocution. Won't do much good or bad for electronics themselves.

    Surge suppressors... You have Line to Line suppression, and Line to earth/ground suppression. If you don't have a green wire ground from your "house power", then an surge suppression power strips/etc. will only do Line to Line protection.

    If you are/will be in a lightning area--Then we should talk more. And the reality is no electronics/power systems will survive a direct strike.

    Anyway--My first cut at answers... Check and ask. I ain't perfect.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • divideoverflowdivideoverflow Registered Users Posts: 7 ✭✭
    edited May 1 #7
    AC Neutral post:
    A few clarifications to what I was trying to convey:
    The Inverter is a Conext SW4048. It does not create a neutral to ground bond, and does not switch a neutral to ground bond. What I was trying to convey is that the neutral connected to their transformer isolates when AC input is present, and "when operating as charger for 120/240VAC source, the internal neutral relay disconnects from transformer so it operates as strictly 240V charger".

    My inverter has one set of AC inputs.




    I do have separate receptacles:


    The transfer switch is between those two inputs, and it does not switch neutral:



    The reason I have two separate receptacles is that I want to bypass my inverter when I'm running a 50 amp service (To be able to exceed the 4000 watt rating of my inverter. It can't supply more than it is rated for while in AC pass through mode). A 50 amp to 30 amp RV adapter plug takes the single hot leg from the 30 amp service and simply jumpers L1 onto L2 (same phase). So it is not true split phase, and my 240V appliances would not function. 

    Honestly, I didn't know what the inverter would do if it received same - phase L1 and L2 inputs. I put in a ticket with Schneider weeks ago, they just this morning sent an email saying they have created a ticket... so they are way behind. The way I have it wired now (trying to play it safe with the inverter inputs), when the transfer switch selects the 30 amp service, the wiring for L2 to the inverter is just dead (which is OK per Schneider, it just de-rates power it can bring in since it unbalances the internal transformer). I would mostly be using the 30amp receptacle to run our small generator (only 1440 watts continuous and 1800 watts max on propane) to charge the batteries in times of low sun. So I would primarily leave my input settings on the inverter to 15 amps unless I was going to be hooked up on the 50 amp shore power service for a while.

    So my inverter will do nothing for the neutral to ground bond. This is why I was thinking of making a "ground to neutral bond plug", which would just be a 50 AMP RV plug end that would stay in my 50 amp plug. So if I'm off grid, the neutral bond is there. If I'm using my generator on the 30 amp inlet (currently no g-n bond), then I just leave the bond plug in the 50A receptacle. And then if I'm using 50 amp shore power, I would remove that bond plug to put in the shore power connection. The only ground - neutral loop risk is if I plugged in shore power to the 30A receptacle - which I would tag out as "generator only", and put a tag on the bond plug "remove if 30 amp shore power is connected" or something.

    The other thing I could do is add a "SOURCE" switch between the transfer switch and the AC Switchgear, which would switch all wires L1, L2 & Neutral between the shore power connection and the "off grid" connection. So I would have to engage or disengage that switch to receive shore power or generator input, but the ground to neutral bond for the off-grid usage would take place there, and be bypassed when shore power is connected. I'm running out of space in my battery box, maybe I could work a side mounted switch lever with 3 pole switch in this same transfer switch that is pictured? It has a ton of empty space. I would just carry the "off grid" neutral-bond connection out of the box, over to where I'll be making my 4/0 battery negative - ground connection.

    Maybe a 3 pole cam changeover switch between my transfer switch and the AC Switchgear. Main risk is 0 being an "off" position, which would leave the neutral ungrounded. I can try and just find a 2 position switch. So I would choose between "shore" or "vessel", and the Vessel option would just be a ground to neutral bond, and would disconnect shore power entirely.


    DC talk and negative bonding to be continued in another post.


  • divideoverflowdivideoverflow Registered Users Posts: 7 ✭✭
    DC Negative - Ground Bonding post:
    So if I bond the battery negative to the chassis ground, then I'll need to disable my charge controller's GFP scheme and install a separate GFP device (like the morningstar GFPD-150V) that allows for a negative ground bond on the battery (and maintains it even when disconnecting the PV array).

    I think I know what I need to do on this front. I can run my 4/0 negative cable from my battery bank bus bar to a vehicle chassis location, and use the #6 awg (max size allowed by the morningstar GFPD) to bond in at my DC Switchgear ground bus (which I will take down to the same chassis bond location and connect).

    BTW, my batteries are obviously not hooked up yet - in progress photo.



  • BB.BB. Super Moderators, Administrators Posts: 30,760 admin
    I am not sure, but it appears that this relay based 50 amp 120/240 VAC transfer switch MAY include 4 switched leads (L1, L2, Neutral). And does come pre-jumpered to allow ground bonding of Neutrals for Generator and Transfer Output Switch.

    https://www.solar-electric.com/pmts-50.html ($128 list price from NAWS/our host)
    https://www.solar-electric.com/lib/wind-sun/PMTS-Install.pdf

    Possibly lift the ground bond on the transfer switch output ("controller"?), and you have the choice with grounding at the genset or the relay ("generator" jumper). And you would have another transfer switch between GEN and AC Inverter output...

    Or, run Controller output to AC input of inverter... Run Power Cord to Power Cord) (floating neutral). And run genset to genset transfer switch input (jumper genset or inside transfer switch).

    A possible alternative wiring for the auto transfer switch... Put AC Cord on Generator input (zero delay needed). And generator on Power Cord Input. Only tie  N+G on the "power cord side" of the relay (or inside the genset).

    When No AC Power, will default to Power Cord In (with N+G Bonding in xfer or genset). If genset running, you have N+G bonding. If AC inverter running, you have N+G bonding.

    If you plug in the shore power (connected to Genset input on xfer switch). When shore power becomes "Hot" (plugged in and energized), the transfer switch will go over to GENSET. This will A) connect L1/L2/N to AC input of Context SW, and B) will not have any neutral bonding.

    This will only work if the Auto Transfer Switch works the way I think it does (no guarantees that the "world" works anything like I want it to). And the "backwards wiring" is based on my memory that the switch only transfer when there is 120/240 VAC on the GENSET AC Input to to the transfer switch.

    Anyway--Just guessing. If you like automation... It could work and not leave you (or a spouse/friends) in the dark if sombody forgot to do a manual transfer.

    Problem is I could not find any really detailed system drawings/controller schematics... So, you may have to contact NAWS (our host) or PowerMax directly. As I understand, the automatic transfer switch is intended to default to shore power, and if the genset starts, have an optional 0 or 7 second delay, and then switch to Genset Power input on the transfer switch.:

    https://www.solar-electric.com/contact/ (NAWS)
    https://powermaxconverters.com/product-category/automatic-transfer-switches/

    I think this is the manual to "your" Contex SW:

    https://www.solar-electric.com/lib/wind-sun/Conext-SW-120-Install-Guide.pdf

    The issue seems to be that the Context SW was not designed for an RV (or boat) electrical system. With a home, the Neutral+Ground bond is always present in the home. And if purely off grid (Genset + AC inverter only), the N+G bonding can take place in the generator or in one of the AC power panels.

    For example, it looks like your manual transfer switch for the 30/50 amp plugs, the Neutral bus is installed on a plastic isolation mount.

    There are inverters and inverter-chargers with  AC1 and AC2 inputs... AC1 typically for 120/240 VAC from utility power. And AC2 is the genset input.

    I looked through the manuals, and they do not talk about 240 VAC only for charging... But the ratings seem to indicate that you can only get ~45 ADC @ ~60 volts if you have 240 VAC and ~12 AAC on the L1/L2 AC connections.

    This is the point where I would step back. I have made some guesses and "Possible" suggestions (like using  an automatic transfer switch).

    I do not see any other "easy" method for wiring your Contex SW in an RV. Using a 3 pole relay/auto transfer switch, or your (3 pole?) manual transfer switch would seem to work.

    I do have a bit of a concern with the 15 & 30 Amp shore power... If I was only in a 15 Amps @ 120 VAC park, not being able to recharge the battery bank or run 240 VAC appliances would be a concern.

    There are 120/240 VAC AC inverter-chargers that simply run at 1/2 charging power with 120 VAC, and will still generate 120/240 VAC output.

    If you run mostly 50 amp @ 120/240 VAC RV parks, and have a 120/240 VAC genset--May not be much of a concern for you.

    And, while folks have wired L1 and L2 for a split phase 120/240 VAC panel for 120 VAC only (tied L1 input to L1+L2 bus bars)... It does work.... However, any 240 VAC system (that does not use Neutral) will see "zero volts" functionally (L1-L2=240 VAC, L1-L1=0 VAC).

    Hopefully you can get some better answers here or by calling the engineers at NAWS and/or PowerMax...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • divideoverflowdivideoverflow Registered Users Posts: 7 ✭✭
    Bill, 
    Thanks again for the continued input.
    I think I'm getting my plans fleshed, and am feeling better about the direction I'm heading.

    Regarding your concern about single phase shore power and generators:
    The SW4048 does generate split phase output from single phase AC input at half power. 

    My inverter owners manual says that if only L1 is powered, I'm just limited to half of the input power (15 amps). Basically it is rated for 15 amps per leg, but the output from the inverter outputs split phase even if only powered by single phase 120V (which is why I bought it in the first place). 15 amps is just fine for this scenario, as I will be running on solar hopefully 99% of the time, and our backup generator we will carry with us is just a little 2000 watt champion dual fuel, which I'll run on propane (so the fuel doesn't go bad), so it will only get 1800 peak / 1440 sustained watts on propane anyway. It is basically just a backup to charge the batteries or pick up critical loads in emergencies. That will be my primary use for that 30 amp input plug. I'll de-rate my input power via the inverter settings when using the generator so I don't overload it. I'm able to set my max charger amperage to 10 amps, and set the input breaker rating to 13 amps so I don't exceed max generator ratings, and the charger can still hit 10 amps with the 80% de-rate of the "breaker capacity".


    The separate 30a & 50a receptacles:
    I briefly revisited the necessity of my choice to have two input locations and the transfer switch. After some research, I did determine that if I tried to use a 50a to 30a cable adapter to use a 30 amp shore power service in my 50 amp plug, I would be feeding the inverter with 2 hot legs of the same phase (L1, L1, & N), which might damage the inverter. Still no word from Schneider, but Magnum has gone on record saying it is a no-no in their very similar product. Since I physically do not have L2 wired for my 30a input receptacle, there is no risk of that scenario as long as no one tries to use one of those adapters on my 50a side! I'm going to put a note on 50a side of the transfer switch box as well indicating: "50a service only, adapters will cause damage".

    If I have 50 amp hookups, I'll likely bypass my Inverter so I can run both my hot water heaters at the same time, whilst blasting the air conditioner and air frying something tasty.

    AC input and G-N bond:
    I really don't care for automatic transfer switches. I hated the one in our previous 5th wheel, and it was a decent one with our integrated Onan 5500 watt generator. I like stuff that is easy to tell what it is doing, and easy to bypass or replace. So for my neutral switching scenario, I've ordered that two position 3-pole cam switch I posted at the bottom of post #7. I've spoken to a few people using it the exact same way. I figure I have to be outside hooking up the shore power cord, and selecting my transfer breaker position anyway, so turning one more handle isn't a big deal.

    I will label the positions "shore" and "inverter N-G bond", and will go in between my 30a/50a selection transfer switch, and my inverter's input breaker. On the shore side, it will be wired up with L1, L2, and the neutral passing through like normal, so the only neutral-ground bond will be at the utility-side (or the generator side). On the inverter setting, I'll have no L1 or L2 cables hooked up, and it will simply have the "house (RV)" neutral jumpered to the chassis ground. This way, there is no way to have the utility neutral or any shore power input connected to the inverter power system unless the switch is toggled to that setting. 


    Ground Fault Protection:
    I did end up ordering the Morningstar GFPD, which maintains the battery negative ground bond and disconnects the solar with a 2 pole breaker.
    https://www.solar-electric.com/morningstar-gfpd-150v-ground-fault-protection-device.html
    It is a much better implementation than the charge controller "1 amp fuse" scheme. Thankfully it is an easy jumper setting to turn off in the charge controller, and adding the new device only requires minor changes to completed wiring and conduit.
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