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DC Ground Rod/Grounding Electrode

First. I do not believe the battery dc negative needs to be "grounded" to the ac earth rod. I believe you are misreading the code.
 
First. I do not believe the battery dc negative needs to be "grounded" to the ac earth rod. I believe you are misreading the code.
If I am, so is Magnum Energy. Below is their simplified diagram showing the abbreviated three possible methods of properly grounding/bonding your inverter to 2017 NEC. All of which either tie the DC GE to AC GE or have a completely separate GE - the latter being the unsafe scenario I was trying to get away from the whole time. The latter also being expensive as the two ground rods needed to be bonded with a conductor no smaller than the largest DC conductor - or 4/0 in my case.
 

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The DC doesn't need to return to earth rod. It can't. The AC needs to return to earth rod. If the combined inverter/charger's case is bonded to the earth rod, the AC failure can return to earth rod and all is well. As the DC can not return to earth rod the DC safety lug must return to the battery negative, I use the negative BusBar. That safety needs be no more than 1 awg size smaller than the main battery cable.
If you want to additionally bond the battery negative or 'ground' lug to the AC earth rod just use a green wire sized to the AC amperes. It will never carry any DC amperes to earth rod.
 
The DC doesn't need to return to earth rod. It can't. The AC needs to return to earth rod. If the combined inverter/charger's case is bonded to the earth rod, the AC failure can return to earth rod and all is well. As the DC can not return to earth rod the DC safety lug must return to the battery negative, I use the negative BusBar. That safety needs be no more than 1 awg size smaller than the main battery cable.
If you want to additionally bond the battery negative or 'ground' lug to the AC earth rod just use a green wire sized to the AC amperes. It will never carry any DC amperes to earth rod.
AC current returns to the source, not the earth. The earth attachment thru a ground rod (grounding electrode) is to reference one leg of the 120v AC power source to Earth potential, prohibiting a shock if you contact earth and that leg of the circuit. and forcing the hot leg of the ac circuit to be no more than 120v above earth potential in a 120v ac circuit. Equipment Grounding also discharges high frequency electromagnetic caused voltage pulses in metallic (current conduction) items when lightning strikes near an electrical system, be it 120v ac or 12v dc. Therefore DC systems in an occupied structure should have all metal equipment and one leg bonded to a ground, be it chassis or ground rod.
 
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I was going through some things as the disagreement in this thread spurred some curiosity, and I believe I’ve discovered the source of it. As Randy said, current returns to the source, not the ground. I like that he said “returns” and not “wants to return” because current always follows the path of least resistance, which tends to be the neutral back to source. As much as I disliked the code requiring GE bonds being such heavy gauge wire, the reason for this is obviously to ensure that the resistance met in taking this path is low enough that it ensures that it DOES in fact take that path.

Now, why does the NEC require this and why is it not universal in many solar systems we all see? That comes down to voltage. I run a 48v system, which sometimes exceeds 60v during heavy charging and equalization. Anything above 60v is no longer considered “low voltage” and must be grounded to earth. I’ve only ever worked with 48v systems, but personally, if I ever built a 24v system, I would follow the same practice - but it would not be required to meet code.
 
I would NOT ground dc to earth, the point it reaches ac make sure it is grounded to earth. NEC is a pain in the ass but dc grounded to earth makes no sense to me. (edited: talking about low voltage and direct ground vs equipment ground)
 
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I would NOT ground dc to earth, the point it reaches ac make sure it is grounded to earth. NEC is a pain in the ass but dc grounded to earth makes no sense to me
The code is frustrating, but we have to be real. NEC is the aggregate of countless highly educated engineers and electricians. We all do our best to interpret and understand - and there is the .01% of the time where they make corrections, but almost all of them are changes to verbiage to make sure the code is interpreted as they intended.

To blatantly disagree with their core logic is not a leap that I myself would feel comfortable taking. To be frank, it starts to feel like arrogance pretty quickly.
 
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The code is frustrating, but we have to be real. NEC is the aggregate of countless highly educated engineers and electricians. We all do our best to interpret and understand - and there is the .01% of the time where they make corrections, but almost all of them are changes to verbiage to make sure the code is interpreted as they intended.

To blatantly disagree with their core logic is not a leap that I myself would feel comfortable taking. To be frank, it starts to feel like arrogance pretty quickly.
In my state they overruled and cut out a lot of the changes made from 2017 to 2020, Im assuming smart engineers did that as well, hopefully.

I didn't mean to blatantly disagree with their core logic, my point was that it is possible to way over-engineer something when planning for every potential failure and situation. I have no problem with better safe than sorry. I also should have clarified that I didn't see the point in running a full gauge ground wire specifically from DC to ground. Most likely everything is going to be grounded (chassis, equipment, etc) through the AC ground rod. I think you know the issue with using two different ground rods in AC based on sub panel code and individual grounding.

If you want to run a 4/0 40 feet it won't hurt anything but it does seem like a waste.
 
I'm not sure of the semantics. Doesn't the AC current, during a short to ground/earth, return to the source?
Could anyone explain how the battery DC negative uses the earth/ground rod to complete a circuit with the DC positive, at any voltage?
As it can't, how does having a 4/0 battery negative cable connected to the earth rod have anything to do with safety?
 
I'm not sure of the semantics. Doesn't the AC current, during a short to ground/earth, return to the source?
Could anyone explain how the battery DC negative uses the earth/ground rod to complete a circuit with the DC positive, at any voltage?
As it can't, how does having a 4/0 battery negative cable connected to the earth rod have anything to do with safety?
If the source is disconnected how can it return to the source? The idea being that the lowest resistance path is normally followed but if you lose a leg you want it going through the 25 ohm ground rather than something else.

DC voltage + can create a circuit with the ground because there is a differential for it to travel. I may be misunderstanding the question.
 
it can't, how does having a 4/0 battery negative cable connected to the earth rod have anything to do with safety?
There’s two licensed master electricians I’ve used for both residential and commercial projects that I’d guess wouldn’t be able to answer that. Transfer switch at a pole: ground rod. Generator: ground rod. Service entrance: ground rod. Solar closet: separate ground rod from inverter and batt negative. Critical load sub-panel: ground rod.

It makes perfect sense now but for many years that’s how I’d see it done or been instructed to do it by some licensed electricians. I just figured it was a rule and they knew something I didn’t.

The recently posted mike holt video sorta summed it up and closed my questions on the practice.
 
I think some have forgotten the function of equipment grounding.

1. To provide a return path to the source that invokes the tripping of an over current device in a circuit ground fault condition. Clears energized equipment surfaces so humans do not provide a ground path (return path for circuit current to source) that could cause electrocution.

2. To discharge electro potential (voltage) imposed on conductive material (metal) when there is a lightning strike adjacent to an electrical system, not a direct lightning strike to the system or its enclosure (structure), but a nearby lightning strike that creates a high frequency dc magnetic pulse on all conducting items near the lightning strike. Equipment grounding including, electrical system grounded conductor, equipment grounding conductors, ground electrode conductor and ground rod termination point to the earth, discharge the high frequency dc pulse to the earth, thereby denying potential build up between adjacent metal conducting items or isolated grounded items that can produce a side flash, perhaps start a fire or electrocute a person that is in some way grounded. The near by lightning strike is the system source, earth is the current return path for that source.

Basically that's why Equipment Grounding is required for both AC and DC electrical systems in occupied structures.
 
If the source is disconnected how can it return to the source? The idea being that the lowest resistance path is normally followed but if you lose a leg you want it going through the 25 ohm ground rather than something else.

DC voltage + can create a circuit with the ground because there is a differential for it to travel. I may be misunderstanding the question.
Just my MSO. The AC returns to the power station through the earth rod during a short circuit condition. The power station could be the grids supplier or it could be a neighborhood generator. The earth rod is not disconnected from the source.
The battery DC negative terminal and positive terminal have a "differential" (wrong word) between them. Connecting the negative terminal to an earth rod does not hurt, but is does nothing for the battery circuit. I certainly would not run 20 feet of 4/0 cable from the inverter. Maybe 8 awg.
 
Just my MSO. The AC returns to the power station through the earth rod during a short circuit condition. The power station could be the grids supplier or it could be a neighborhood generator. The earth rod is not disconnected from the source.
The battery DC negative terminal and positive terminal have a "differential" (wrong word) between them. Connecting the negative terminal to an earth rod does not hurt, but is does nothing for the battery circuit. I certainly would not run 20 feet of 4/0 cable from the inverter. Maybe 8 awg.
You missed the point. Connecting A/C ground to ground rod DOES NOT RETURN short circuit condition (current) to the power station. The ground rod provides a '0' volt reference point for the electrical system grounded conductor and grounded equipment. It also provides a path for high frequency dc pulse induced on electrical conduction items by near buy lightning strike magnetic pulse in the occupied structure, protecting equipment and people in the structure.
Tying the ground electrodes together electrically in a electrical system occupied structure stops large current surges on the equipment grounding conductors in that structure when lightning strikes near the structure, but not lightning strikes to the structure.
 
Zil, try this.
Drive an auxilary ground rod in the earth (not the structure ground rod, but a second one you install for this test).
Connect a conductor from a circuit breaker in a NEC code compliant occupied structure ac system distribution panel.
Connect the other end of that conductor to the auxilary test ground rod.
Turn the circuit breaker on.
If its a 120v ac system, the current flowing thru the conductor will be 120v / 25 ohms = about 5 amps. The circuit breaker will not trip.
Why is this true ?
(of course, be safe, do live dead live tests on any wires you touch before touching them, wear safety glasses, and possibly stand on a rated rubber blanket when handling the conductor or isolate yourself from ground some other way.)
 
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Yes i got myself mixed up posting without my breakfast whisky. The rod itself provides some limited lightning protection, the real return is the neutral/ground connection at the service entry.

My question is and will remain; Why connect a battery negative to the AC circuit earth ground rod with cable equal to the P & N battery cables?
 
Yes i got myself mixed up posting without my breakfast whisky. The rod itself provides some limited lightning protection, the real return is the neutral/ground connection at the service entry.

My question is and will remain; Why connect a battery negative to the AC circuit earth ground rod with cable equal to the P & N battery cables?
250.166
(A) Not Smaller Than the Neutral Conductor

Where the dc system consists of a 3-wire balancer set or a balancer winding with overcurrent protection as provided in 445.12(D), the grounding electrode conductor shall not be smaller than the neutral conductor and not smaller than 8 AWG copper or 6 AWG aluminum.

(B) Not Smaller Than the Largest Conductor

Where the dc system is other than as in 250.166(A), the grounding electrode conductor shall not be smaller than the largest conductor supplied by the system (both AC and DC), and not smaller than 8 AWG copper or 6 AWG aluminum.

***ABOVE - Here's your code. We can all post analogies all day long, but at the end of the day, the answer to your question is "because the code requires it." If you consider your skill set to be beyond the reproach of the NEC, I wish you the best.
 
250.166
(A) Not Smaller Than the Neutral Conductor

Where the dc system consists of a 3-wire balancer set or a balancer winding with overcurrent protection as provided in 445.12(D), the grounding electrode conductor shall not be smaller than the neutral conductor and not smaller than 8 AWG copper or 6 AWG aluminum.

(B) Not Smaller Than the Largest Conductor

Where the dc system is other than as in 250.166(A), the grounding electrode conductor shall not be smaller than the largest conductor supplied by the system (both AC and DC), and not smaller than 8 AWG copper or 6 AWG aluminum.

***ABOVE - Here's your code. We can all post analogies all day long, but at the end of the day, the answer to your question is "because the code requires it." If you consider your skill set to be beyond the reproach of the NEC, I wish you the best.
You left out 250.166 C, D and E exceptions. (A grounding electrode is not always a 'grounding rod'). C,D&E allow smaller gauge wire for grounding electrode conductors in certain cases.
 
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250.162
DIRECT-CURRENT CIRCUITS AND SYSTEMS TO BE GROUNDED
A) Two-Wire, Direct Current Systems. A 2-wire DC System supplying premises wiring and operating at greater than 50 volts but not greater than 300 volts shall be grounded.
(three exceptions are itemized)
B) Three-Wire, Direct Current Systems. The Neutral conductor of all 3-wire, DC systems supplying premises wiring shall be grounded.

These code paragraphs are for premises wiring. There is specific direction for RV, mobile equipment grounding in Article 551. Article 551 does not apply to 24v or less DC power sources. ANSI RVIA-LV requirements apply to the DC systems in Rv's. RVIA-LV does require the '-' pole ofthe battery to be grounded to the chassis.
In the USA.
 
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First. I do not believe the battery dc negative needs to be "grounded" to the ac earth rod. I believe you are misreading the code.
In the USA, you are right. The battery '-' needs to be grounded to the system grounding electrode (not necessarily an ac earth rod).
 
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