off grid setup questions related to grounding and awg

[Sunking]

and seems to be some sort of catastrophic failsafe recommended by the manufacturer without a clear engineering basis.

Yeah I know what that catastrophic failure will be with 100 amps flowing inside that little inverter box will be. The supply wire will be just fine even if a number 6 was used. It will make a nice 1200 watt hot plate to cook your dinner on.

[SunEagle]

Yeah I know what that catastrophic failure will be with 100 amps flowing inside that little inverter box will be. The supply wire will be just fine even if a number 6 was used. It will make a nice 1200 watt hot plate to cook your dinner on.

I believe the manual for the Morningstar 300watt inverter is confusing. It states you need a 100amp fuse on the DC side and then gives an example of using a #6 wire between the battery and inverter which is not a good match for that 100amp fuse.

If you look in the specs it states you can use up to a #2 awg wire on the DC side. So if you use that #2 wire then the 100amp fuse makes sense.

[Sunking]

I beleive the manual for the Morningstar 300watt inverter is confusing. It states you need a 100amp fuse on the DC side and then gives an example of using a #6 wire betweent the battery and inverter which is not a good match for that 100amp fuse.

That is what I am trying to say. You cannot use manufactures examples. This is not unique and quite common with manufactures instructions that do not conform or comply with known engineering practices and electrical codes. That is why I went off on it. Bonding the neutral is a huge NO-NO as it is only allowed in 1 place and 1 place only. Otherwise you will force lload current onto grounding conductors.

[arnold_ky]

Thanks for all the replies. I am no electrician by any means as you can probably tell from my diagram. This is been somewhat of a project I have been digging into off and on to learn about electric. At some point I'm sure I will upgrade the inverter as I will mostly just be using it to power a few lights for now.

After reading the posts, I did forget to put the "ground wire" coming out of the AC panel going to the receptacles, etc..

So I can use the 100amp fuse if I go with a 2 AWG cable. If I stay with the 6 AWG I will need a 40 amp fuse .


Also I don't know if I seen it mentioned in the previous posts, but would the grounding in the diagram be correct with the AC and DC going to the same earth ground ?


Thanks again!

[arnold_ky]

Also, would the fuse block from blue marine be doing the same thing as the big baby box that was suggested earlier?

Thanks.

[Amy@altE]

The Big Baby Box was a suggestion to switch from fuses to breakers for your over current protection. You can use either/or. I spoke to MorningStar, I believe they are going to answer the questions regarding wire and fuse sizing themselves, but short answer is, yes, if you want to use #6 wire, that's fine, use a 60A fuse or breaker.

The point people are making about the AC grounding is to make sure to bond neutral to ground at one spot, don't have 2 AC ground/neutral connections. Grounding isn't my specialty, I believe if the DC ground is connected to earth ground, you can use the same ground, if it is close by for your AC ground. If the DC ground rod is far away, there may be a small potential, so you should do a grounding rod for the AC. Again, not my strongest subject, so I'd be happy to have input from others.

[arnold_ky]

Thanks for all the help Amy.

[arnold_ky]

Would the size of the fuse / breaker going from the charge controller + to the battery bank be the same size as the fuse going from the battery bank to the charge controller (40 or 60 amp) ?

[Sunking]

Would the size of the fuse / breaker going from the charge controller + to the battery bank be the same size as the fuse going from the battery bank to the charge controller (40 or 60 amp) ?

No. Needs to be no larger than the CC is rated for assuming the wire is rated to carry what the CC can supply.

[arnold_ky]

Thanks SunKing. You're probably getting annoyed by some of the questions, but I think I'm making some progess.

Here is where I am at as far as the drawing. I decided to go with the breaker box vs the fuses. Let me know if that looks correct. One thing I am really unsure of is the Invertor's ground connection. Per the manual it says to ground it to the AC neutral which is how I have it on the diagram, but I am not sure of this.

pic03.jpg

[Sunking]

Thanks SunKing. You're probably getting annoyed by some of the questions,

No not at all, I am just trying to keep you safe and point out the flaws. What I still do not know or can figure out why such a small inverter to back feed a AC breaker panel. A single receptacle in anyones home is capable of nearly 2000 watts. a 300 watt inverter connected to a house is like peeing on a house fire. Just one little mindless mistake and it blows. Even one item can trip it.

[Sunking]

Here is where I am at as far as the drawing. I decided to go with the breaker box vs the fuses. Let me know if that looks correct. One thing I am really unsure of is the Invertor's ground connection. Per the manual it says to ground it to the AC neutral which is how I have it on the diagram, but I am not sure of this.

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Personally I would not do it. That DC breaker box is some distance from the source (battery) leaving the battery cables unprotected. If you should take a fault anywhere along the length you will have a fire and explosion on your hands.

[arnold_ky]

The reason for the 300w invertor is because that is what I currently have. I will be very cautious on the load until I get a larger invertor. Like I said, just a few led lights would be all I would be running.

As far as the distance between the batteries and the breaker box, it will only be a few feet at the most.

[arnold_ky]

I see what you are saying with the battery cables. I will go with the terminal fuses.

As far as not doing this setup, was that do to the size of the invertor or the dc breaker box?


Also on the ground. I read quite a few places online where you should terminate the dc and ac grounds to the same grounding rod with a separate wire for each, but seems to be hard to find a definite answer.


Here is the updated drawing.

pic04.jpg

[sensij]

Also on the ground. I read quite a few places online where you should terminate the dc and ac grounds to the same grounding rod with a separate wire for each, but seems to be hard to find a definite answer.

The NEC offers a definite answer. Do you know which version of code applies to you? There are two types of grounding... the equipment ground conductor (EGC), and the ground electrode conductor (GEC). The GEC is only necessary if your array is grounded, and has more stringent requirements about size and splicing. The EGC is always necessary. There was another thread recently in which these topics were discussed, with several good links in the thread to outside resources.

The Morningstar controller requires that the DC voltage of the array be ground referenced, so a GEC is required. You can sink a dedicated electrode for the DC as long as that electrode is bonded to the AC electrode. You could also run a splice free bond wire directly from from the DC disconnect to the AC electrode ("permanent" splices, using approved methods, may be allowed). Some panels require that the positive side be grounded, but most ground the negative. I don't see the panel part number in the thread, so I can't say for sure.

Even with the DC voltage ground referenced, you still need an equipment grounding scheme. I don't see any ground wires going out to your array... is that just an omission in the drawing?