Author Topic: How do you deal with inverter grounding on an off grid building?  (Read 1996 times)

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Offline Red Squirrel

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I'm adding electrical to my shed and it will be solar.  To do things properly I want to tie the neutral and ground together at the panel and put in a grounding rod.  Only issue is it seems most inverters don't have a floating ground, but rather it is referenced to neutral and hot, basically 60 volts difference.  Can I simply omit that ground completely or will that cause weird issues?  This is not typically something they advertise on sites that sell inverters so it's kind of a gamble if I just buy another.
 

Offline mtdoc

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #1 on: June 01, 2018, 03:51:19 pm »
I assume this will be an off grid system with a 48V nominal battery bank (hence the “60V difference”).

If so, just bond battery negatve (and neutral) to ground.
 

Offline Bratster

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #2 on: June 01, 2018, 04:08:24 pm »
Don't connect neutral and ground on a split output inverter like you have. At best it will just turn off /Overload, at worst it will blow up.

The 60 volts to ground has nothing to do with input voltage. the cheap inverters basically have a center Tapped Output with ground being the center tap.


Look for a quality inverter and not the cheap crap. If it has a GFCI outlet on it you should be okay. Also if it has a transfer switch built-in you should be good as well.

If you're looking at almost anything that's a modified sine wave high frequency inverter they are usually 60v-0v-60v outputs and you cannot use them in your application IMO.



Also keep in mind that most inverters that can have the neutral bonded to ground already do that themselves seeing as they are intended to be the power source.
So in that case you would not want a second neutral ground Bond at your panel.

A lot of inverters that have transfer switches built in will give you the option of them doing the neutral to ground Bond or letting you do it separately.

If it only has a GFCI outlet on it for the output and no hard wire option then it definitely has a neutral to ground Bond internally.


If it does have a hardwire option but no transfer switch then it's anybody's guess whether or not the neutral to ground bond is removable. (Well, without cracking it open obviously)

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« Last Edit: June 01, 2018, 04:44:59 pm by Bratster »
 

Offline mtdoc

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #3 on: June 01, 2018, 04:16:51 pm »
Ah, i see I misunderstood the question (I must be tired, it’s late here).  You meant 60V as in 1/2 cycle of 120V inverter output.

In any case, the answer is the same.  Battery negative, inverter neutral and ground all bonded to earth is typical IME.
« Last Edit: June 01, 2018, 04:23:28 pm by mtdoc »
 

Offline Bratster

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #4 on: June 01, 2018, 04:41:13 pm »
Ah, i see I misunderstood the question (I must be tired, it’s late here).  You meant 60V as in 1/2 cycle of 120V inverter output.

In any case, the answer is the same.  Battery negative, inverter neutral and ground all bonded to earth is typical IME.
I agree on all of them being connected and earthed like you say. For the correct application

however that will not work with the inverter that he seems to have currently.

Ground is at 0 volts, line is at 60 volts and neutral is at 60 volts 180 degrees out of phase.

That's how the cheap inverters work almost all the time.



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Offline Red Squirrel

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #5 on: June 02, 2018, 02:18:52 am »
Yeah I can't connect the neutral to ground with the current inverter and the issue is, they don't realy advertise this so I can try to buy a new inverter but I won't know if it will be the same until I get it.  Ideally I want to get a 2000w inverter ($$$$) so that if I decide to plug in the weed whacker or power drill or something, I can. Of course with my current 60w panel I won't get that far if I try to run a big load for a long time. 

So my question is, can I simply completely omit the inverter's ground, and then make my own at the junction box?  This particular inverter is made of plastic so I don't really have to worry about the chassis.  Though I do plan to get a more powerful one eventually so maybe I'll get lucky and it will have a floating ground or be tied to neutral.  At that point I can remove the bond at the junction box.

This is a 12v system, but I may do a 24v or 48v system later down the road.  My plan is to upgrade to one or two >200w panels but I can't seem to find anywhere I can source those out without paying an arm and a leg for shipping.   Once I get this system setup my goal is to eventually do a 48v system for the house and run my server stuff off it too.
 

Offline f4eru

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #6 on: June 02, 2018, 02:29:35 am »
Quote
So my question is, can I simply completely omit the inverter's ground, and then make my own at the junction box?
Nope.
You have to ground the negative of the battery, if the inverter is not isolated.
 

Offline Red Squirrel

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #7 on: June 02, 2018, 02:35:26 am »
Quote
So my question is, can I simply completely omit the inverter's ground, and then make my own at the junction box?
Nope.
You have to ground the negative of the battery, if the inverter is not isolated.

I don't know if that will work either because the battery may not be floating vs the inverter ground.  Ex: If I do that it might short out.  I think they skipped some steps in the making of this inverter such as not using transformers so nothing is isolated from each other.    I'm more worried about the AC ground at this point because of safety, ex: if the chassis of something or a wiring box becomes energized I want it to go to earth ground.   If the batteries float I can ground that too though but I'm more worried about getting the AC ground right.   Idealy when I upgrade the inverter everything will be better isolated but like I said, they rarely advertised this kind of thing so it's hit and miss.
 

Offline f4eru

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #8 on: June 02, 2018, 02:38:56 am »
Yes.
If the inverter has a grounding point, use that.
 

Offline IanB

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #9 on: June 02, 2018, 02:49:26 am »
Ground is at 0 volts, line is at 60 volts and neutral is at 60 volts 180 degrees out of phase.

This statement is inconsistent and cannot be meaningful. Neutral is by definition at 0 volts referenced to ground. If a wire is at 60 volts relative to ground then it is not neutral, it is hot.

The system described is a 60-0-60 V system with two hot wires and a center-tapped ground. (This is a common system on construction sites in the UK as it limits the ground fault shock voltage to 60 V.)

I'm adding electrical to my shed and it will be solar.  To do things properly I want to tie the neutral and ground together at the panel and put in a grounding rod.  Only issue is it seems most inverters don't have a floating ground, but rather it is referenced to neutral and hot, basically 60 volts difference.  Can I simply omit that ground completely or will that cause weird issues?  This is not typically something they advertise on sites that sell inverters so it's kind of a gamble if I just buy another.

If your shed is a completely islanded system and isolated from anything to do with the mains supply, then I do not see why you cannot use the ground provided by the inverter as the ground wire for the receptacles in the shed. Obviously you cannot tie it to either of the hot wires and you cannot use a traditional home installation breaker panel. Perhaps there is a special kind of breaker panel that can be used with this kind of inverter, or maybe it is just designed to connect directly to an extension cord in a similar manner to a standalone generator?

It seems you may run into issues of code compliance if you attempt a fixed installation with this system? Perhaps it might be better to keep it as a portable (non-fixed) system?
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Offline IanB

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #10 on: June 02, 2018, 02:54:46 am »
Or, why not just treat the 60-0-60 V split phase supply similarly to the 120-0-120 V split phase supply that comes into a house? Use a normal panel, use double pole breakers, and wire the outlets accordingly, with two hot wires and a ground?
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Offline IanB

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #11 on: June 02, 2018, 02:58:27 am »
To do things properly I want to ... put in a grounding rod.

If you connect your system to a grounding rod I think it will increase the risk of electric shock, since it will create a conductive path between any exposed conductors and grounded objects. Logic suggests the system will be safer if you leave it floating and do not try to ground it (in this respect somewhat like an isolation transformer).
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Offline f4eru

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #12 on: June 02, 2018, 03:50:49 am »
Quote
If you connect your system to a grounding rod I think it will increase the risk of electric shock
Yeah. Sometimes, but mainly not.

Today, in a lot of countries which have RCCDs mandatory on all circuits, as in my country, isolation transformers are more dangerous than non-isolated circuits.
You are not warned and put safe when you touch the first wire on an isolated circuit, you get the full shock with no protection directly when you touch the second.
On a 30mA RCCD, it never happens, there's nearly always a path to ground for 30mA, and you're protected, at least on 220V, less so on 110V
So I strongly recommend the TN-S earthing scheme if possibl, with a RCCD:

http://www.electrical-installation.org/enwiki/Definition_of_standardised_earthing_schemes

But beware!
The output of a non-isolated inverter is not a sinus with respect to battery- ( which is PE often)
The output of this inverter puts a half sine on one conductor, the other half sine on the other.
This is fine, but it adds a DC component to GND.
So if you use a RCCD downstream, please take one that also protects against DC faults.
 

Offline Bratster

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #13 on: June 02, 2018, 04:25:36 am »
Ground is at 0 volts, line is at 60 volts and neutral is at 60 volts 180 degrees out of phase.

This statement is inconsistent and cannot be meaningful. Neutral is by definition at 0 volts referenced to ground. If a wire is at 60 volts relative to ground then it is not neutral, it is hot.

The system described is a 60-0-60 V system with two hot wires and a center-tapped ground. (This is a common system on construction sites in the UK as it limits the ground fault shock voltage to 60 V.)

I'm adding electrical to my shed and it will be solar.  To do things properly I want to tie the neutral and ground together at the panel and put in a grounding rod.  Only issue is it seems most inverters don't have a floating ground, but rather it is referenced to neutral and hot, basically 60 volts difference.  Can I simply omit that ground completely or will that cause weird issues?  This is not typically something they advertise on sites that sell inverters so it's kind of a gamble if I just buy another.

If your shed is a completely islanded system and isolated from anything to do with the mains supply, then I do not see why you cannot use the ground provided by the inverter as the ground wire for the receptacles in the shed. Obviously you cannot tie it to either of the hot wires and you cannot use a traditional home installation breaker panel. Perhaps there is a special kind of breaker panel that can be used with this kind of inverter, or maybe it is just designed to connect directly to an extension cord in a similar manner to a standalone generator?

It seems you may run into issues of code compliance if you attempt a fixed installation with this system? Perhaps it might be better to keep it as a portable (non-fixed) system?
I dont't disagree, for correct terminology.

But cheap inverters have a neutral terminal, a ground terminal, and a line terminal.

And neutral is not 0v on them.

They are intended to have the load plugged directly into them.

I really think the op should throw this inverter in the trash and get a proper one.

Pure sine wave. GFCI on the output.

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« Last Edit: June 02, 2018, 04:27:44 am by Bratster »
 

Offline mtdoc

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #14 on: June 02, 2018, 04:29:10 am »

If your shed is a completely islanded system and isolated from anything to do with the mains supply, then I do not see why you cannot use the ground provided by the inverter as the ground wire for the receptacles in the shed.

Yes, I agree. 

Also,on the cheap inverters I have seen, the only ground connection I've seen is the chassis ground which should be bonded to earth - as should the ground wire from the receptacles.

Quote
Obviously you cannot tie it to either of the hot wires and you cannot use a traditional home installation breaker panel. Perhaps there is a special kind of breaker panel that can be used with this kind of inverter, or maybe it is just designed to connect directly to an extension cord in a similar manner to a standalone generator?

I don't see why you could not use a traditional home breaker panel (if wired correctly of course).  But in any case, for an off grid shed, I would use something like this Midnite baby box enclosure.  Midnite solar makes other larger enclosure/breaker panels both DIN mount and panel mount versions.
 

Offline Bratster

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #15 on: June 02, 2018, 04:34:43 am »
The problem with a traditional breaker panel is the neutral from the cheap inverter is not at 0v.


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Offline IanB

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #16 on: June 02, 2018, 04:38:56 am »
The problem with a traditional breaker panel is the neutral from the cheap inverter is not at 0v.

Yes, but a traditional breaker panel is a two-pole device with two hot bus bars and a center neutral/ground. Just like the output from the inverter...

Even so, I prefer mtdoc's suggestion of using devices intended for connection to a solar inverter.
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Offline Red Squirrel

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #17 on: June 02, 2018, 06:30:42 am »
The issue with using the ground provided by the inverter is that it's not a proper ground because it's referenced to both the hot and neutral by 60 volts.  Things like GFCI outlets would probably not work correctly as neutral should be 0 volts to ground and hot be 120.  Also one of the advantages of tying neutral to ground is that only the hot becomes dangerous.  Ex: if your finger touches the inside of a light socket you wont get shocked. 

So that's why I'm thinking, not bother using the inverter ground, and put my own ground rod, and then tie the AC ground to that ground so all the electrical boxes etc are at zero potential to earth ground so there's less risk of a shock.  Neutral would also be at zero potential with hot being 120 as they would be tied at the main junction box.  Using a large junction box instead of a breaker panel as I essentially just have one 120v 15 amp circuit (the inverter is only 300w so technically less but everything is rated to 15 amps)  I don't really want to treat this as split phase as that's not really proper for a 120v system as it would be 60v per side and not 120.  Suppose I could use a transformer to isolate the AC but that's getting a tad overkill for a shed.  I may also replace the junction box with a nema box so I can have DIN breakers/relays as I want to have outside lighting that's on a timer for example so all the controls could be in there.   

There's no point in trying to get a new inverter since I have no way of knowing if the new one will be properly isolated or not.  This is not something that is typically advertised.  You find out once you get it and measure it.  I do plan to upgrade it at some point but not now.   The charge controller I use is odd too.  When I originally built this solar system I wanted to tie the solar ground and battery ground together so I can properly measure the voltages from a MCU but I can't because the battery negative is referenced to the solar negative, and it's not by 0 volts. 

Basically the proper way would be to build my own charge controller and inverter so I can design it properly with every negative/ground/neutral being 0, but that's a project for another time when I have more electronics knowledge.

Also this particular inverter has a plastic chassis, so as far as safety grounding for the inverter itself it does not really need any. 
« Last Edit: June 02, 2018, 06:37:26 am by Red Squirrel »
 

Offline mtdoc

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #18 on: June 02, 2018, 06:43:06 am »
I think you are making this more complicated than it needs to be.

Place your ground rod. Bond battery negative, neutral and ground to it.  Done.

Solar panel frames and any other exposed metal should also be connected to the earth ground.
 

Offline Red Squirrel

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #19 on: June 02, 2018, 07:08:28 am »
I think you are making this more complicated than it needs to be.

Place your ground rod. Bond battery negative, neutral and ground to it.  Done.

Solar panel frames and any other exposed metal should also be connected to the earth ground.

But those are not isolated from each other because of how the charge controller and inverter works.  If I do that, it will short out the system.  That's why I'm asking if I can just skip the ground from the inverter and make my own ground.  The inverter ground is +60v from what the ground should be (same as neutral) and the battery ground is a few volts from the solar negative (it changes based on solar input).  Nothing is isolated or referenced to zero.  If I tie it together it will short out.

The inverter and charge controller don't seem to be properly designed, but from what I read this is an issue with lot of inverters.  A lot of people try to connect it to their house (with power off and isolated from grid) without realizing this and blow them.

I could add transformers in between each stage but I will get some losses from that.  Would probably be cheaper to do it on the DC side and use a push-pull controller.

I'm still thinking I just skip the inverter ground though and ground my system independently, trying to figure out if/why that would be a bad idea.
« Last Edit: June 02, 2018, 07:15:23 am by Red Squirrel »
 

Offline mtdoc

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #20 on: June 02, 2018, 07:58:34 am »
I'm sorry, but there must be some confusion here.


But those are not isolated from each other because of how the charge controller and inverter works.
What is not isolated from what? 
Quote
If I do that, it will short out the system. 
What will short?   As long as positive and negative (PV output, CC input/output, and battery output) are not shorted and as long as inverter hot is not shorted to neutral/ground, everything should be fine.

Quote
Nothing is isolated or referenced to zero.
  If you bond battery negative, inverter neutral and ground to the earth ground you create they will be referenced to zero as they should be!

Quote
If I tie it together it will short out.
Yes everything bonded to the your new earth ground will be tied together as they should be.



 

Offline IanB

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #21 on: June 02, 2018, 07:59:27 am »
The issue with using the ground provided by the inverter is that it's not a proper ground because it's referenced to both the hot and neutral by 60 volts.  Things like GFCI outlets would probably not work correctly as neutral should be 0 volts to ground and hot be 120.  Also one of the advantages of tying neutral to ground is that only the hot becomes dangerous.  Ex: if your finger touches the inside of a light socket you wont get shocked.

I think you are overthinking this, and really your concerns are unfounded. If you plug a 120 V device into the inverter it will work. Furthermore, if there is an accidental short circuit to the inverter ground there will be a high current that will trip the breaker/blow a fuse. So that will work too. Lastly a GFCI looks for a current imbalance between out and return. If there is a leak to ground there will be an imbalance and the GFCI will trip. So that will work. In short, everything will work.

Bear in mind that your house wiring is just the same with 240 V circuits. There are two hot wires, neither is neutral, and ground is 120 V away from either of them. Nobody claims that 240 V circuits in houses are "wrong" or that they do not have a proper ground.

You are not trying to design something sophisticated here, you just have a simple solar inverter for your shed to power some low power devices like lights. Just wire it up to your junction box, connect it to a few receptacles and be done with it.

(Also, don't worry about that 60 V electric shock from light sockets. The only way to get that shock is to touch the inside with one hand and the outside with another hand at the same time. And why would you ever do that? Every child knows not to poke fingers inside light sockets.)
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Offline IanB

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #22 on: June 02, 2018, 08:01:42 am »
Also, it seems mtdoc is proposing that you create a new ground of your choice by floating the inverter and bonding its "neutral" wire to an external ground of your own making. That also could work. It's up to you how to proceed.
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Offline mtdoc

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #23 on: June 02, 2018, 08:03:51 am »
Also, it seems mtdoc is proposing that you create a new ground of your choice by floating the inverter and bonding its "neutral" wire to an external ground of your own making.

Yes, but I would not call that floating.

He could float the inverter by not bonding neutral to his new earth ground, but for a permanent installation, I'd advise against it.
« Last Edit: June 02, 2018, 08:06:47 am by mtdoc »
 

Offline IanB

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #24 on: June 02, 2018, 08:09:34 am »
Yes, but I would not call that floating.

I think it is floating before you choose a ground reference. After you ground it is not floating any more. What you cannot do is ground it in two places at once, for example you cannot tie together the terminal on the inverter marked G and the terminal on the inverter marked N as this will create a short circuit and destroy the inverter. You either have to pick G or N as your ground point and use it consistently.

Tying ground to battery negative will only work if there is complete isolation between the battery side and the AC side of the inverter. Otherwise there could also be a damaging short circuit.

Personally I would tend to wire the terminal marked G on the inverter to the ground pin on the various sockets and receptacles. There must be a reason why that terminal is provided on the inverter.
« Last Edit: June 02, 2018, 08:12:14 am by IanB »
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Offline mtdoc

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #25 on: June 02, 2018, 08:12:11 am »
Here is a nice concise diagram of off grid inverter wiring from Morningstar.   Perhaps this helps.

I think it is floating before you choose a ground reference. After you ground it is not floating any more. What you cannot do is ground it in two places at once, for example you cannot tie together the terminal on the inverter marked G and the terminal on the inverter marked N as this will create a short circuit and destroy the inverter. You either have to pick G or N as your ground point and use it consistently.

G and output N of the inverter normally should be bonded - it should not destroy the inverter. Once you bond G and N together to earth ground they are electrically the same point.

Tying ground to battery negative will only work if there is complete isolation between the battery side and the AC side of the inverter. Otherwise there could also be a damaging short circuit.

Well if there is no isolation there you will have problems regrardless of whether or not battery negative is earth bonded.

« Last Edit: June 02, 2018, 08:29:51 am by mtdoc »
 

Offline Red Squirrel

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #26 on: June 02, 2018, 08:54:33 am »
I think there may be a bit of misunderstanding.  The ground output of the inverter (the ground pin of the socket) has 60 volts potential between neutral or hot.  In a normal electrical system neutral and ground should be bonded, but if I do this, I will create a 60 volt short and damage the inverter.

The charge controller has some odd circuitry which causes the negative of the PV side and the negative of the battery to not be isolated from each other either and are at a different potential (I forget what) so I cannot bond those either. 

I'd have to measure battery and AC output to see if those are isolated or not but I have a feeling they arn't either.

So for now I will leave the PV and battery side float, but I'm more concerned about the AC grounding, so I'm proposing to ignore the inverter's ground, and supply my own from the ground rod which will tie to the AC ground and the neutral at the main junction box that feeds everything else.  This will ensure that the AC ground, wiring boxes, and neutral are all referenced to earth ground as it should be in a normal AC system. 

This would be a somewhat temporary solution though as I do plan to buy a better inverter, so if I'm lucky the new inverter will have proper isolation between input/outputs so that I can bond everything correctly without causing issues.  But that's not something I'll know until I pick an inverter and measure it.  We are very limited here in Canada as far as PV related products so I have slim pickings. 
 

Offline IanB

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #27 on: June 02, 2018, 09:11:57 am »
So for now I will leave the PV and battery side float, but I'm more concerned about the AC grounding, so I'm proposing to ignore the inverter's ground, and supply my own from the ground rod which will tie to the AC ground and the neutral at the main junction box that feeds everything else.  This will ensure that the AC ground, wiring boxes, and neutral are all referenced to earth ground as it should be in a normal AC system.

I see what you are saying, but I don't understand why you want to install a ground rod and tie things to it. This is not a normal AC system, it is more like a portable gasoline generator. With a portable generator you just run it and then plug things into it.

So I still think you are overthinking this and trying to make it much more than it is. It's just a small power supply in your shed. That's all. Like any other power supply, just plug things into it and use it.
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Offline mtdoc

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #28 on: June 02, 2018, 09:24:21 am »
The ground output of the inverter (the ground pin of the socket) has 60 volts potential between neutral or hot.  In a normal electrical system neutral and ground should be bonded, but if I do this, I will create a 60 volt short and damage the inverter.

Hmm, ok I guess I see the confusion now.  I have not seen that - even on the cheap inverters I've looked at.  I'm still not sure that bonding negative to ground on the output of the inverter would cause an issue - it would depend on the inverters internal wiring. 

Quote
The charge controller has some odd circuitry which causes the negative of the PV side and the negative of the battery to not be isolated from each other either and are at a different potential (I forget what) so I cannot bond those either. 
OK, but I never said you should bond the CC input negative to your earth ground with battery negative.  CC inputs should be left floating. (see diagram in link I posted)



 

Offline Red Squirrel

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #29 on: June 02, 2018, 09:25:36 am »
I was thinking more from a safety standpoint.  If power accidentally contacts metal work like junction boxes or an appliance I am plugging in.   With a proper ground it will short out and trip the breaker (which I don't have now...suppose I should, but inverter probably would shut down anyway) I guess it's not the end of the world, but I'm just thinking there's potential for power to be used in a wet location too so risk is a bit greater.   Though I guess a GFCI could work too.   It's all connected up now and works fine though so maybe you're right I can just leave it.
 

Offline f4eru

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #30 on: June 02, 2018, 09:28:01 am »
Quote
This is not a normal AC system, it is more like a portable gasoline generator. With a portable generator you just run it and then plug things into it.
Nope.
You have to ground it also.
And not like this :
https://imgur.com/rbAo0Vc

It's a safety issue to not ground a generator, especially when plugging class I devices in it, which need an earth to be safe.
 

Offline mtdoc

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #31 on: June 02, 2018, 09:35:52 am »
So I still think you are overthinking this and trying to make it much more than it is. It's just a small power supply in your shed. That's all. Like any other power supply, just plug things into it and use it.

Yes, I agree.  If he leaves the output of the inverter floating, it is essentially the same as the output of the typical portable generator (though technically you should ground reference those - few people do). There will be some shock risk if any non double insulated appliances, etc are plugged into it since there is no GFCI outlet.

RV inverter set ups are typically floating relative to earth but still, battery negative, neutral and ground are bonded to the frame of the vehicle which acts as the "earth" while inside it.
 

Offline IanB

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #32 on: June 02, 2018, 10:41:53 am »
I was thinking more from a safety standpoint.  If power accidentally contacts metal work like junction boxes or an appliance I am plugging in.   With a proper ground it will short out and trip the breaker

This is true. Which is why you should wire the terminal on the inverter marked G or ground to the ground wire in the appliance cables or receptacles.
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Offline Red Squirrel

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #33 on: June 02, 2018, 11:00:11 am »
I was thinking more from a safety standpoint.  If power accidentally contacts metal work like junction boxes or an appliance I am plugging in.   With a proper ground it will short out and trip the breaker

This is true. Which is why you should wire the terminal on the inverter marked G or ground to the ground wire in the appliance cables or receptacles.

This will create 60 volt potential between ground and either hot/neutral though (the inverter has no ground screw, just the ground outlet output).   Would this be an issue?  Right now this is how it's connected but I feel that's not right.  The neutral and hot are not bonded given it would cause a 60 volt short.  Do I just run my ground to a rod and call it a day and not worry about the neutral and ground bonding?   I doubt it would be to code but I'm not too worried about that, I just want it to be safe. 
 

Offline IanB

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #34 on: June 02, 2018, 11:04:24 am »
It's a safety issue to not ground a generator, especially when plugging class I devices in it, which need an earth to be safe.

That's not true according to this article: https://c.ymcdn.com/sites/www.csda.org/resource/resmgr/imported/Sept%2007%20Safety%20Counts.pdf

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In my mind, there are two different ways to use a generator. The first is as an isolated system in which the generator is powering a specific piece of equipment like concrete saw through the receptacles on the generator. I call this the cord and plug system.

If you are using the cord and plug system, typically you do not need to supply an earthgrounding rod with the generator. There are no other sources of electricity, lightning surges, or fault currents that you would need to contend with. The housing/frame of the generator will serve as an adequate ground for the fault currents generated by that particular generator.

Broadly speaking, the purpose of grounding and bonding is to prevent any metal parts of the system or structure getting raised to higher voltages than the real earth ground caused by external current or voltage sources (like lightning, fallen power cables, other mains power cables in the vicinity, and so forth).

If you have a completely isolated and portable power supply that is far away from any other electrical systems, then there are no other stray currents to need protection against. In this instance the portable power supply can be left floating. However, the ground terminal in receptacles should still be solidly connected to the ground terminal and metal frame of the generator.

I would consider a simple floating and isolated PV generator on a shed far away from mains wiring to be like a portable generator. (I'm thinking a box on the wall, a couple of receptacles and a light fixture.) It is not the same as running a mains feed to a sub-panel in the shed. In any case, 300 W hardly even counts a generator. It won't run more than a few lamps and it is barely worth connecting it to plug sockets. All you could power would be some battery chargers for cordless tools.
« Last Edit: June 02, 2018, 01:31:26 pm by IanB »
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Offline IanB

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #35 on: June 02, 2018, 11:08:15 am »
This will create 60 volt potential between ground and either hot/neutral though (the inverter has no ground screw, just the ground outlet output).   Would this be an issue?

No, it's not an issue. As previously mentioned this is the standard system used on UK construction sites where they use 55-0-55 V step down transformers for power tools (where the 0 V center tap is grounded). It limits the maximum electric shock from an insulation fault to 55 V, which is much less damaging than the normal mains voltage.
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Offline Red Squirrel

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #36 on: June 02, 2018, 11:11:50 am »
This will create 60 volt potential between ground and either hot/neutral though (the inverter has no ground screw, just the ground outlet output).   Would this be an issue?

No, it's not an issue. As previously mentioned this is the standard system used on UK construction sites where they use 55-0-55 V step down transformers for power tools (where the 0 V center tap is grounded). It limits the maximum electric shock from an insulation fault to 55 V, which is much less damaging than the normal mains voltage.

Good to know, guess I'll just keep it as is then.  I'll put in a grounding rod or two and tie it in to that ground then.   I'll just solder the wire straight to it and drive it in the ground.  My main water valve is not that far, I might tie to that too.
 

Offline NorthGuy

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #37 on: June 02, 2018, 11:35:25 am »
... the battery ground is a few volts from the solar negative (it changes based on solar input).

This is because one (or more) of the wires you used to connect them is too thin (and thus has high resistance). When current flows through it, the wire's resistance produces voltage drop - Ohm's law at work.

Unless you have extremely unusual solar charger, solar negative is directly connected to the battery negative.
 

Offline Red Squirrel

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #38 on: June 02, 2018, 11:54:49 am »
... the battery ground is a few volts from the solar negative (it changes based on solar input).

This is because one (or more) of the wires you used to connect them is too thin (and thus has high resistance). When current flows through it, the wire's resistance produces voltage drop - Ohm's law at work.

Unless you have extremely unusual solar charger, solar negative is directly connected to the battery negative.

It's just a cheap PWM controller, so I do plan to replace it eventually.  Would love to be able to reference everything to ground, as it would enable me to actually easily measure voltages via an MCU.  When I originally built this portable system I wanted to be able to measure PV voltage and battery voltage but could not do both as they are not referenced to ground.    This is the PCB:



I may eventually design my own too, would make a fun project and I'd be able to design it with proper isolation/bonding in mind.  It's hard to source this kind of stuff anyway outside of cheap Ebay/Amazon jobbies straight form China.  So if that stuff has not caught on fire (yet) my own stuff might be just as safe. :P   Actually I'll probably want smoke detectors that alert me in the house/phone in that shed considering it has electrical. 
 

Online KE5FX

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #39 on: June 02, 2018, 12:02:46 pm »
Every portable generator instruction manual I've ever seen warns that it should be grounded.  No instruction manual ever says why, or cites the relevant electrical code.  From my point of view, that's a green light to ignore the warning.   >:D   

The only reason I can think of to ground a generator is to prevent static electricity buildup that could prove hazardous during refueling.  You have rotating parts, rubber belts in some cases, that sort of thing.  There is likely to be a good counterpoise in the form of the connected cord(s) and device(s).  I only use propane generators, never gasoline, so I don't see that as an issue, but it's worth keeping in mind.
 

Offline NorthGuy

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #40 on: June 02, 2018, 01:17:29 pm »
This is the PCB:

A very small one, probably designed for car batteries. Looks like it has N-channel FET and switches the low side. So, the positives of the battery and the panel must be connected, perhaps through the big diodes we see over there. You can reverse engineer the power connections just by looking at the PCB traces.
 

Offline f4eru

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #41 on: June 02, 2018, 05:47:39 pm »
Quote
As previously mentioned this is the standard system used on UK construction sites where they use 55-0-55 V step down transformers for power tools
They use 110V in UK for power tools ?
That's strange.
 

Offline IanB

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #42 on: June 02, 2018, 05:56:34 pm »
They use 110V in UK for power tools ?
That's strange.

For commercial use on construction sites. Ordinary consumer tools at home run off the standard mains supply.
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Offline f4eru

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #43 on: June 03, 2018, 08:25:02 pm »
Quite a strange thing.
Probably it has historic reasons.
doesn't really make much sense today, coz it tries to protect against touching one conductor, which RCCDs are available now, and it doesn't really do anything for touching both conductors, and it complicated construction...

Are US style plugs used in this setup ?
 

Online b_force

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #44 on: June 03, 2018, 10:14:49 pm »
Meanwell has some very good solar inverters for a fair price (around 1500-3000W)
They also provide a lot of information and support, so I would just give them a call or send an e-mail.
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Offline Seekonk

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #45 on: June 09, 2018, 01:35:50 am »
Everyone keeps saying 60-0-60.  While that is RMS, it is a H bridge output and the output should be about 140V to battery common if it is not electrically isolated. Many inverters do not even connect the ground pin.
 

Online NiHaoMike

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Re: How do you deal with inverter grounding on an off grid building?
« Reply #46 on: June 09, 2018, 02:28:30 am »
Some standalone inverters are isolated and some are not. I have torn down a CAT 1kW unit that is isolated and has ground fault sensing. Funny thing is that because it's isolated, grounding either side of the output will not trip the ground fault protection. My best guess is it's a backup in case the isolation gets bridged somehow.
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