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.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.
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.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 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.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
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.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.
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.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?
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 can't, how does having a 4/0 battery negative cable connected to the earth rod have anything to do with safety?
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.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.
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.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.
250.166Yes 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?
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.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.
In the USA, you are right. The battery '-' needs to be grounded to the system grounding electrode (not necessarily an ac earth rod).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.