Newbie here, questions on proper grounding of DIY home system

Should my battery pack be earth grounded? If so can is it wise to use the same ground rod my combiner box is on or just use a different grounding rod? All responses greatly appreciated!

I do not ground mine. Does your inverter specify?

Ampster thanks for the response. See thats whats confusing me to a degree, My Victron 150/60tr instructions say to connect to the negative side of battery as close to the battery as i can, but if battery is earth grounded then anything i connect to the negative side will be earth grounded. Not sure if everything needs to be earth grounded like my BMS for say.

I did not see anything in your response that quoted Victron saying to ground your battery. What are you confused about. This is a home not a car.

I apologize you didnt, Ive just been in thought about this system and i jumped to the Victron CC, apologies. Correct this is a DYI home set up. To reply to your response about the inverter, yes mine does require to be grounded. Going back to what i asked, Ive read some forums saying that the battery packs should be earth grounded, then some saying no or they dont earth ground their battery pack? Why earth ground or why not earth ground?

Bhogue said:

Ive read some forums saying that the battery packs should be earth grounded, then some saying no or they dont earth ground their battery pack?

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I would go to those forums and ask that question. I can't read the mind of every poster. Perhaps there are specific reasons that would apply to specific use cases? Perhaps they are off the grid or their equipment says to earth ground. Perhaps it depends on the voltage? It all depends on where you are standing. Do you understand the risks of earth grounding a 48 volt pack versus a 12 volt pack?

I understand and that makes since. No actually i do not know the risks of earth grounding 48V verses a 12V, but you have my undivided attention due to i have a 48V pack.

This is a very complicated topic, partly because of terminology confusion, and partly because of the differences in construction of charge controllers and inverters.

If I understanding correctly, you are asking if one of your battery bank conductors should be tied to the system earth ground conductor so that the battery potential is always relative to earth ground. However, the earth grounding conductor often is also bonding equipment chassis, and depending upon the construction of your inverter or charge controller, this may create other problems or requirements.

Before taking any advice, you should look carefully through your equipment installation instructions. For instance, I've been looking at my SMA inverter instructions and they say:

If you ground the battery, you can ground it at the positive terminal or at the negative terminal with a grounding conductor. SMA Solar Technology AG does not recommend grounding the battery. If the battery is grounded, the enclosure of the Sunny Island must also be grounded. This additional grounding is no substitute for the grounding at connections AC1 und AC2.

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So they are saying, you can ground either side of the battery and make it work, but then you have to have the appropriate inverter chassis bonding, and you have to realize that the AC outputs are still isolated from that ground.

I don't think anyone could properly answer your question without knowing a lot of details about your equipment.

Some people view it as a risk because once one side of the battery is tied to the grounding system, a fault in the conductor for the other side of the battery to any metal in the system could create a high current fault and fire risk, and if it is tied to earth ground, the risk of shock to a grounded individual is increased. Other people say the best route is to ground the system and then use a DC ground fault protection device so that the battery will be automatically disconnected if there is a short somewhere rather than having bad insulation on a conductor go undetected.

Sorry that this is a very long post that really doesn't give you an answer. I hope it does show some of the complexity in deciding what to do.

For a home system, you are required to have ground fault protection. Some charge controllers have it built in, like Midnite Classic and Schneider, and the new Outback FlexMax 100. Others do not, like Victron, Morningstar, and the smaller 2 Outbacks. If you are using a Victron charge controller, you need an external ground fault protection device. Regardless if it is internal or external, the GFP device is where the negative and ground are bonded. Therefore, by bonding negative to ground, the negative terminal of the battery is grounded. You only want the system bonded in one place, so you would not do an additional ground at the battery terminal. If your battery has a metal case, that's a different story, it may require you ground the case. If so, the manual would tell you to.

I have this picture saved on my computer, but I think I got it from Victron's Unlimited Wiring document from the 'Resources' section. I do recall that it's for an off grid system, but you mention a home DIY, but don't mention grid tie or off grid. So this may help, or not help and add to the confusion.

Hankcurt, thanks for the reply, no worries on the length of your post it was very helpful in understanding the complexity of battery pack grounding. You are absolutely correct in saying terminology confusion because im already there to some degree. Totally makes since what you said bout not taking advise but referring to the equipment manuals. Agreed, I was just asking and trying to better understand the dos and donts because ive already have some problems. Never knew grounding could be this complicated for different systems or the set up. If i were to detail my system and the way i have it config. could you give me your recommendation if you would earth ground it?

I'm just trying to figure out my own installation, which probably makes me poorly qualified to give recommendations.

I would pay attention to what @SolarQueen recommends ( I guess we are all assuming you are in the U.S.) And if you are in an area that enforces local codes, you should inquire if there are any variances from the NEC for your community.

With that in mind, I encourage you to post more details because there is are a lot of helpful people on the forum.

@Solar Queen, GMB thanks for replying and the helpful understanding as well. GMB my system is off grid. @SolarQueen, i do have a Victron CC so i would need a external GFPD, Great info i did not know that! No i do not have a metal battery case. @hankcurt, I totally understand trust me i do. I just saw Where Solar Queen and GMB replied and yes, a lot of helpful and knowledgeable people here for sure! Yes in in US, Alabama and have no idea if they have codes on solar or not.

Great news. In Alabama, you only need to comply with NEC2014. That means you don't have to worry about rapid shutdown. Trust me, you are lucky. So just get a GFPD, and use that for your ground to negative bond. You are good to go. Here's a good schematic showing how Outback recommends using it. https://www.outbackpower.com/downloads/documents/wiring_diagram/north_american_fp1_off-grid.pdf .

What size charge controller are you using? Also, what do you have for a DC breaker box? Does it take DIN Rail or panel mount breakers?

So, I did a little reading, and now I'm not sure if I understand the scope of what @SolarQueen said.

The codes are pretty clear that an arc fault/ground fault protection device is required for 'PV systems' on buildings. And by the definition of what a ground fault protection device has to do, its clear that a ground is required at the device. So I'm clear on all that.

However, I can't find anything applicable to the battery system. The NEC code Article 706, under Scope, says it applies only to DC battery systems over 60 volts. I'm not sure that the code requires ground fault protection at the battery, unless that is included as part of the 'PV System'. I looked for a definition of the 'PV System' and didn't see one, but the diagrams distinguish the 'PV System" from the 'ESS System'. So if a person was just running a Sunny Island as a grid powered battery backup with no photovoltaic system, does the ground fault requirement still apply?

I'm not sure if the Midnight Classic arc fault protection also detects faults down stream of the charge controller, or if it only detects them upstream. At any rate, it can't disconnect the battery from the inverter. I'm thinking that appropriate wire sizing relative to the battery over current protection is the actual protection between the battery and the inverter.

Anyway, I might be splitting hairs there with the exception that I need to figure out if my Midnight Classic charge controller also ties one of its DC outputs to ground because I need to account for that in the wiring of the Sunny Island. I'm sure that's in the Midnight Classic documentation.

hankcurt said:

So, I did a little reading, and now I'm not sure if I understand the scope of what @SolarQueen said.

The codes are pretty clear that an arc fault/ground fault protection device is required for 'PV systems' on buildings. And by the definition of what a ground fault protection device has to do, its clear that a ground is required at the device. So I'm clear on all that.

However, I can't find anything applicable to the battery system. The NEC code Article 706, under Scope, says it applies only to DC battery systems over 60 volts. I'm not sure that the code requires ground fault protection at the battery, unless that is included as part of the 'PV System'. I looked for a definition of the 'PV System' and didn't see one, but the diagrams distinguish the 'PV System" from the 'ESS System'. So if a person was just running a Sunny Island as a grid powered battery backup with no photovoltaic system, does the ground fault requirement still apply?

I'm not sure if the Midnight Classic arc fault protection also detects faults down stream of the charge controller, or if it only detects them upstream. At any rate, it can't disconnect the battery from the inverter. I'm thinking that appropriate wire sizing relative to the battery over current protection is the actual protection between the battery and the inverter.

Anyway, I might be splitting hairs there with the exception that I need to figure out if my Midnight Classic charge controller also ties one of its DC outputs to ground because I need to account for that in the wiring of the Sunny Island. I'm sure that's in the Midnight Classic documentation.

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The Midnite Classic has both Arc Fault and Ground Fault protection. You ground the Classic, and its internal GFP bonds it to negative. Does that answer your question?

SolarQueen said:

The Midnite Classic has both Arc Fault and Ground Fault protection. You ground the Classic, and its internal GFP bonds it to negative. Does that answer your question?

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In regards to the Midnite Classic it does. Thanks.

The other part of my questions was more code related. I did find that they define a 'PV System' as

Photovoltaic (PV) System. The total components and subsys‐
tem that, in combination, convert solar energy into electric
energy for connection to a utilization load.

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And they define Utilization as basically "end use equipment"

Utilization Equipment. Equipment that utilizes electric energy
for electronic, electromechanical, chemical, heating, lighting,
or similar purposes.

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So by that I understand any requirements for the 'PV System' apply to the storage system and inverter, as they are conversion equipment, not utilization equipment.

Because the original question was about the energy storage system, I was trying to figure out if the protection provided by the charge controller met any code requirement for arc fault detection down stream of the charge controller. Or if such a requirement even existed.

Arc fault is for solar panels, so the charge controller takes care of that for the whole system. Likewise, the negative and ground of the PV system are protected by the GFP in the controller. No additional equipment is needed.

Thanks

@SolarQueen, what im actually trying to do is heat water. I have a secondary tank with 2 700W 48V elements. What I have and the conf. as of now on my board i have a 150/60tr Victron CC. I have 2 baby boxes, one with an 80 amp breaker, battery side the other baby box a 30 amp on the PV side. My battery pack is 48V 200AH LiFePO4 cells. 300A Smart Ant BMS. Very close but outside mounted i have my MidNight combiner box with 3 10amp breakers. Dont have my panels yet but Thinking of Trina Soligent 310W panel and config. them 3S3P.

@SolarQueen, thank you for the spec sheet but my system is a stand alone system. But even with my system a GFP is still required aint it?

Bhogue said:

@SolarQueen, thank you for the spec sheet but my system is a stand alone system. But even with my system a GFP is still required aint it?

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The only exception I see for the ground fault protection requirement in the 2014 code is:

Exception: Ground-mounted or pole-mounted PV arrays
with not more than two paralleled source circuits and with
all dc source and dc output circuits isolated from buildings
shall be permitted without ground fault protection.

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So if your solar power is generated on top of a building or is used in a building, you need the ground fault protection.

Apologies hankcurt, i saw the spec sheet and thought solarqueen was talking about what i had.

We have a large barrier island inside the city limits of Corpus Christi . the sand is 50 feet deep. when the water table gets low there is no ground at all with a grounding rod. During drouth times we go long periods of time that those grounds ground nothing. Still no damage to people or property. I can't see the need for them.

Believe it or not i know what your talking about, I travel a mostly with my job and have spent quite a bit of time in Corpus through out the years. I understand and agree with what your saying. Ive been thinking and like my boat, theres no ground so all connected to negative. I believe thats what im gonna do plus put a GFP on my combiner box and go with it