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Off grid Breaker box, generator / solar inverter hook up

Tat2rtist

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Sep 6, 2020
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I have an off grid cabin, I installed a breaker box, and wired it for a generator. The generator I use is an inverter type with a floating neutral. So inside the breaker box I have bonded neutrals and grounds. Now I am getting ready to hook up solar, and want to hook up my inverter to this breaker panel. I have seen in one article about an inverter it says do not hook up to the box if the neutral wires and grounds are bonded in the box. Anyone have any experience with this? Should I change my box and put in a separate ground bar so the neutrals and grounds are separate? And how will this effect the floating ground inverter generator when it is hooked up? Thanks in advance for any advice.
 
That may not be floating neutral, but rather hot is 60V from chassis/battery and "neutral" is 60V, but 180 out of phase so you get 120V.
Check voltages between everything with inverter operating by itself.
"ground" neutral to chassis of the inverter with a light bulb and check again.

Having "neutral" hot at 60V could be a problem in a couple ways, shock hazard and fire hazard because unfused.
It would function isolated. But better to have an inverter that allows neutral to be grounded, or to add an isolation transformer to this one.
 
I would not pay attention to what you read in an unrelated article. I would pay attention specifically to what your inverter manual instructs. For my particular inverter, it requires bonding of the neutral and ground, at the DC power center, which I did. For the generator-charger circuit, it wants a 3+1 wire connection, meaning L1, L2, N, and G. So, the generator's N and G are connected to the inverter, at the AC2 input, as indicated in the manual.
 
I'm confused about neutral bonding with floating generator as well. I have a 2000W floating neutral inverter generator with a 120V receptacle. At the receptacle Hot to Ground is 60V and Neutral to Ground is 60V (Hot to Neutral is 120V). I want to tie this into a panel in my completely remote off-grid install (no grid utility power around). At the panel I run the generator hot to a breaker that acts as my "Main" panel breaker and powers one leg of the box (a few building LED lights and plugs run off other breakers on that same leg). I run the generator neutral to the neutral bar and generator ground to the ground bar in the panel. The panel ground bar is grounded to Earth. Now, everything works in the building, however, with the breakers off there is still 60V from neutral to ground at any outlet in the building. This would be expected because the 60V neutral to ground at the generator receptacle is being transferred to the building. So, do I just bond the neutral bar to the ground bar at the panel to solve this issue? Would I then get 0V from neutral to ground at the building receptacles? Or would this be a short condition from the generator's perspective (and maybe harm my generator)? Like I mentioned, everything works in the building, but that 60V at building outlets with all the breakers off is a potentially dangerous condition if someone leaves the generator running, but flips OFF all breakers and thinks there should be no voltage at the outlets. Thanks for any help you can provide.
 
With a DMM you see 60 VAC between neutral and ground of the inverter.
Try putting a lightbulb across those terminals. See if it lights, and what voltage is present.
If voltage goes to zero, you can ground it. If it remains 60V you can't.

Running 60 VAC through the neutral means there is no fire protection in case of a fault. Breakers only open the hot, not the neutral.
You could use all 2-pole breakers so both legs are interrupted, wiring the cabin for 120V only.
Not completely safe because 60 VAC "neutral" could be touched where it comes to socket of a lamp or chassis of an (antique) TV.

You could isolate inverter chassis and batteries, then tie "neutral" of inverter to neutral of breaker panel.
Inverter and batteries now carry 60 VAC (other terminal of battery carries more, AC + DC) so those do reach hazardous voltages.
Best to have in a locked room, and have 2-pole breaker disconnecting it from breaker panel. (i.e. use both phases of breaker panel like earlier suggestion, but ground the one called "neutral".)

Or, get an isolation transformer. Inverter delivers +/-60VAC split-phase, transformer produces 120V isolated so one leg can be grounded. Ground inverter chassis. Probably best and most direct solution, some inefficiency, heavy and costs a bit but can find used. A toroid transformer (I see them on eBay) would be higher efficiency.
 
Thanks for the quick response and great info! I'm intrigued about the 120V only panel option because I am fine with doing that, but want it safe and as "normal" to a household situation as possible in terms of safety and fire protection in case of a fault in the circuitry. I have no intention of ever needing or running 240V. So, if I use all 2-pole breakers and label one pole as my "Neutral" (and then just never use the neutral bar in the panel) the attached diagram seems to me as a way to accomplish this 120V only panel wiring option. It seems safe since if the outlet circuit breaker is flipped to OFF then no power will go to the cabin circuit (outlets). And if the "Main" is flipped to OFF then no power goes to the two poles so no power out to the cabin circuit. I would label the panel with all kinds of warnings to never attach to any kind of 240V power source. The one concern I have is about the grounding. Should the panel earth ground be removed and the generator should be grounded to earth instead? BTW, the generator receptacle ground has continuity to a grounding screw on its frame. Thanks again.
 
Panel ground bus would be grounded and used for outlets. Good to have that run to a ground rod.
Neutral would not be used, so whether green screw used to ground it or not wouldn't matter.
GFCI won't provide the protection desired unless it opens both legs so normal GFCI outlets won't be sufficient. Portable GFCI like on cord of a hair dryer will protect.
Possibly a 2-pole GFIC breaker meant for 120/240VAC would work, possibly not. Depends on how its circuitry is powered, if it needs 240V between legs. You could get one and try it.
You're basically implementing 60/120V split phase, and running 120V appliances off both legs. On/off switches in appliances will only open one leg. You could use all 2-pole switches for lights, etc. as if they went to a 240V fixture; that would open all hot wires so 60V not present when changing a bulb.

But also consider isolation transformer as an alternate method. On eBay I think you'll find a few toroids with sufficient VA rating, for a few $hundred.
 
Thinking about it more, the isolation transformer sounds like the more "normal" and safer outcome. I will have to research that option more because I don't know anything about them. Any recommended documentation links to learn more about it would be appreciated. Thanks again!
 
I linked a couple from eBay:


That was for 120/240V conversion, either isolated or not works. You need 120/120 isolated, or 120 to 120/240 isolated

I think the second listing can provide 2000VA isolation, either 2, 120V output in parallel or in series for 120/240V
You would wire 100V and 20V in series to get 120V.

I power up one winding with AC, check voltage of others. When I find two leads from separate (isolated) windings and determine the voltage each produces to it's other lead, I then join the two windings together at one end, measure between the other leads to see if I got them in parallel or in series. That way I can label them +/- or red/black and figure out what series/parallel connection each needs. You just have to be careful not to short a winding, or parallel two different voltage windings. A low value fuse or breaker on the AC source while figuring it out would be good. A 12VAC or 24VAC transformer as source would limit risk/damage.

With transformers, there is a current limiting per winding (ampacity and heating), also VA limit through the magnetic core. To some extent you can pull more current from one winding if the other isn't loaded, less heating of the core, but the wire has its resistive heating limit too.
I'm setting mine up with a fan controlled thermostat and manual reset overtemp thermostat opening a relay (due to high current, 9000VA). You can get a manual-reset thermostat which will handle 10A, maybe 20A. One or two of those could protect both primary windings in parallel, or each primary winding separately, depending on current handling.

250V, 20A, $7 delivered:


Airflow is good too. Does your inverter have a fan which comes on when it works harder? That warm air ducted over the transformer would probably keep it cooler than still air.
 
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