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DC Ground Rod/Grounding Electrode

Netsua

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Jul 22, 2021
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My inverter is connected to the ground bus bar/grounding conductor in both the AC Main panel as well as the AC sub-panel to which it is connected. There is a lug on the inverter casing specifically for "DC Ground." The manual shows this ground being connected to the battery enclosure - and also indicates that it must be bonded to the ground rod with wire that is as large as the largest DC wire.

This would involve running ~20+ feet of 4/0 cable in my system. Which I would do... but my enclosure is made of wood - and thus no reason/method of grounding. Is there any reason the DC side of the system cannot float? Everything is bonded to my primary grounding electrode on the AC side of course. The ground/neutral bond is here at the meter as well.
 
In the absence of a metal enclosure, I almost wonder if the idea would just be to go directly to earth from the negative bus bar and then tie this to the GEC and inverter case. Ground threads never get exposure lol. I found like 6 that have no answers ha
 
The more I read the more confused I get. This system has been running for a year without any issue... but it sounds like my DC grounds are boned. I know AC electric backwards and forwards... but if anyone can help me with the DC ground and ground/neutral bond, I’d appreciate it a ton
 
I don't have my Battery case earth grounded either but it should be.
Tying the batteries DC ground to earth would be a bad idea. The idea around the earth grounding is mainly to protect the BMS inside from surges caused by lightning. I had this exact problem when a bolt of lightning struck very close to my house and the Inverter threw an error that the DC/OV. I suspect that it means the DC over voltage.
I would run the wire from that battery casing to your earth ground and that should be the all protection you need.
 
There is a lug on the inverter casing specifically for "DC Ground."
Under fault conditions the case could be DC live or AC live.
To carry the DC fault current and thus blow the fuse/trip the breaker feeding DC to the inverter, connect to battery negative one size down on DC feed cables to the inverter.
To carry AC fault current add a second cable from the inverter case to the AC ground point in the installation. Suggest a CSA twice that of the AC live feed cable from the inverter.

Mike
 
The more I read the more confused I get. This system has been running for a year without any issue... but it sounds like my DC grounds are boned. I know AC electric backwards and forwards... but if anyone can help me with the DC ground and ground/neutral bond, I’d appreciate it a ton
In dc circuits there is no ground/neutral bond. There is only negative and positive. There is a Positive and a Negative connection on the inverter for the battery connections. There is a Case Lug on most inverters. It can serve two purposes, 1. Reference something like an RV chassis to the inverter's ac current earth ground. This is not your configuration 2. Provide a safe negative connection if something should fail. In this configuration the case should connect to the battery negative with no less than one awg smaller cable than the battery feed cables. It should not connect to the negative cable at the inverter, but to the main negative BusBar or battery negative terminal. It has nothing to do with your ac current ground/neutral connections. You should have those using the 'green/bare' wire from the ac supply cable from the inverter to the sub panel.
 
Zil, I'd like to support you in your statement, but to do so would require me to find a NFPA NEC 70 section, RVLIS-LV section, or ABYC E-11 section to quote to support your statement in the US. There is also the Chance that the UL standard for Inverters used on RV's may require a battery '-' circuit connection and an AC ground to grounding elecrode connection.
 
Grounding Basics - Mobile Systems :
(lots of info here, takes time to digest for me)
 
Netsua, is you Electrical SYStem in a bricks and sticks or a RV.
If Bricks and Sticks, does the structure have an AC Electrical service ?
 
Zil, I'd like to support you in your statement, but to do so would require me to find a NFPA NEC 70 section, RVLIS-LV section, or ABYC E-11 section to quote to support your statement in the US. There is also the Chance that the UL standard for Inverters used on RV's may require a battery '-' circuit connection and an AC ground to grounding elecrode connection.
I don't think OP is talking about mobile system. But that is what I'm saying, I hope. Inverter AC ground to system ground. DC negative case lug to battery negative.
 
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With battery current there is no "earth/ground". There is positive and negative. An inverter needs two safety connections. 1; DC. Case lug to battery negative terminal. 2; AC. Case to earth/ground/green/bare at subpanel if using a subpanel. Other wise to outlets.
An inverter/charger needs it's mains feed earth/ground connection per NEC and other codes.
 
Sorry guys, haven't been keeping an eye on this lately and missed the responses. I did finally make a decision - which I believe was the correct one.
I ran a short 4/0 wire to a smaller bus bar - which is where I ran all my DC grounds. I then ran that to the System Bonding Jumper in the primary AC service panel. I ran my ground rod from that point also - on the AC side.
ground.png
 
The more I read the more confused I get. This system has been running for a year without any issue... but it sounds like my DC grounds are boned. I know AC electric backwards and forwards... but if anyone can help me with the DC ground and ground/neutral bond, I’d appreciate it a ton
Welcome back and damn nice drawing. I think this thread may accomplish it's goal.

Questions:
What country are we talking about?
Is this system in a structure or other?
Were you running your system with GEC-DC conductor (that is scribbled over in red ink) connected to earth in the past?
 
I’m in the US and yes this system is in a structure.

My original plan was to run the system with both the GEC-DC, as well as the GEC-AC as per 2017 NEC. But in order to be code compliant, I would have also needed to bond the two with 4/0 wire - which would be almost 40 feet in my system.

So it was cost prohibitive, but more so, there’s a fair amount of evidence that the 2017 actually got this wrong and it’s a dangerous practice. I’ve heard it might have been fixed in 2020 NEC, but I cannot confirm.
 
I’m in the US and yes this system is in a structure.
There’s a video in this thread that is fairly informative.
I’m not old but I’m definitely not young- I apprenticed w/ two different master electricians in the late 1980s which gave me a good foundation in many ways, some not so good! I have learned things over the years that revealed some instructions I got were very, very wrong.
This site here has recently had several grounding issues with inverters that gave me new perspective on grounding and grounding rods for example.

I recommend watching that video for the perspective.

>> Your inverter seems like a very nice unit! Just read over the specs. I’d imagine the instructions were NEC correct at time of printing. However, the multiple bare/earth/green/neutral connections caught my attention after watching the referenced video and you apparently observed similarly:
My original plan was to run the system with both the GEC-DC, as well as the GEC-AC as per 2017 NEC. But in order to be code compliant…..but more so, there’s a fair amount of evidence that the 2017 actually got this wrong and it’s a dangerous practice. I’ve heard it might have been fixed in 2020 NEC, but I cannot confirm.
While I’m no EE or electrician I, too, care about safety and wouldn’t want live 120VAC running around the house without any clothes on.

I’d review the vid and perhaps contact the manufacturer for updated guidance on the issue. You can’t be the only one, right?!
 
There’s a video in this thread that is fairly informative.
I’m not old but I’m definitely not young- I apprenticed w/ two different master electricians in the late 1980s which gave me a good foundation in many ways, some not so good! I have learned things over the years that revealed some instructions I got were very, very wrong.
This site here has recently had several grounding issues with inverters that gave me new perspective on grounding and grounding rods for example.

I recommend watching that video for the perspective.

>> Your inverter seems like a very nice unit! Just read over the specs. I’d imagine the instructions were NEC correct at time of printing. However, the multiple bare/earth/green/neutral connections caught my attention after watching the referenced video and you apparently observed similarly:

While I’m no EE or electrician I, too, care about safety and wouldn’t want live 120VAC running around the house without any clothes on.

I’d review the vid and perhaps contact the manufacturer for updated guidance on the issue. You can’t be the only one, right?!
I want to make sure we’re speaking the same language (figuratively of course). I’m super familiar with Mike Holt. He has 2k dollars of my money in his bank account because I used his course to pass my 2017 NEC test. He’s the one that led me down the path of potentially ignoring the NEC in this case. Are we talking about the same thing? How using multiple ground rods in a system can be dangerous?
 
Where does the NEC Code require the battery negative to bond with the earth ground rod using battery cable? I believe the ac green wire is sufficient to bond the ac and negative battery.
In our off site generation we use multiple ground rods tied together but with only one wire, one rod, to the panel grounding buss. I'm told the rods only provide lightning protection as in general they have too much resistance to earth.
 
I want to make sure . Are we talking about the same thing? How using multiple ground rods in a system can be dangerous?
yes
Almost everything I was taught when I was young that I believed from qualified people even turns out to be more common sense and less what you’re told!

That was why I mentioned it
 
Where does the NEC Code require the battery negative to bond with the earth ground rod using battery cable? I believe the ac green wire is sufficient to bond the ac and negative battery.
In our off site generation we use multiple ground rods tied together but with only one wire, one rod, to the panel grounding buss. I'm told the rods only provide lightning protection as in general they have too much resistance to earth.


I don’t have my code book handy, and it does appear to have been corrected in the 2020 NEC, but we’re still on 2017. Below is the reference - it was in regards to table 250.66. I didn’t want to create an unsafe system AND spend a ton of money on 40+ ft of 4/0 just to pass an outdated code - thus, my solution.
 

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