I agree with this, for me at least, grounding is a bear to really wrap my head around, and fully understand conceptually, particularly for unorthodox systems where there aren't necessarily established 'best practices' or clear code to follow.I think it is important to realize that grounding is not a strict "right or wrong" choice. Depending on your application will determine how you need to ground or bond your system.
Understanding this definitely helped me make sense of it as well. This video was very helpful for me in understanding ground conceptually. It also taught me I hadn't truly conceptually grasped voltage either.The best way to understand ground is to think of it as a reference voltage of 0V for the system. Or as a sink for excess electrons. That is how I make sense of it all.
To clarify, is what you are envisioning/describing keeping the DC negative and the vehicle chassis totally separate/isolated from one another. Or are you describing using dedicated DC negative and ground conductors connected to a busbar which is then bonded to chassis and the negative battery terminal (such as in the image below):But a big point in my original comment is that the chassis is not a true earth ground. It is insulted from earth ground due to the tires of the vehicle, so excess charge accumulation will have nowhere to go (if that is your intentions with grounding). You can still use the chassis as a negative bus, but there are no benefits compared to using a tinned copper bus bar.
3.11 Grounding to earth or to other designated ground
For safety against electrical shock, the metal chassis of unit is required to be grounded to the Earth Ground or to the other designated ground. for example, in a mobile RV, the metal frame of the RV is normally designated as the Negative DC ground / RV Ground. Similarly, boat Ground is provided in the boats.
An Equipment Grounding Connector (5 in fig. 3.8) has been provided on the metal chassis for connecting to the appropriate ground through the Equipment Grounding Conductor (EGC). This Equipment Grounding Conductor (EGC), when appropriately bonded to Earth Ground, helps to prevent electric shock and allows over-current devices to operate properly when ground faults occur. The size of this conductor should be coordinated with the size of the over-current devices involved. Marine installations require the size of this conductor to be of the same size as the battery Negative wire.
7.5 Mobile installations
A mobile installation is an installation that operates independently from the grid. When it connects to AC power it usually connects to the grid at different locations and/or generators. For example, like boats, vehicles or mobile back-up power systems. In this chapter a boat installation is used, however, this information can be used for any mobile installation.
A mobile system does not have an earth stake. So, something else in its place is needed to create a central earth potential. All touchable metal parts of the boat or vehicle must be connected to each other to create a local earth. Examples of metal parts in a boat or vehicle are: chassis, hull, metal fluid pipes, railing, engine, power point earth contacts, lightning conductors and the earth plate (if present).
A mobile system typically connects to a variety of power sources it is sometimes not clear which of the leads in the shore power supply is connected to earth or if earth is connected at all. Also phase and neutral may have not been wired correctly. Connecting a supply like this to a mobile system can potentially create a short circuit to earth. Or earth is missing completely.It also matters if the mobile system connects to power or if it is disconnected from power and running autonomously.
So, as regards grounding on an RV setup, with a multiplus inverter, where it can sometimes have a grid connection, which diagram below has the correct grounding configuration .... A, B or neither...please explain your conclusions(Grounding cables in green)
A
View attachment 26067
B
View attachment 26068
I'm struggling to follow the logic here, I don't see these as separate questions, I think they are very much related.I like equipment enclosures and PV frames tied to vehicle chassis.
Whether or not battery negative should be tied to chassis is a separate question
Inverter/chargers designed for mobile or marine applications--specifically UL 458 inverters--internally switch the Neutral-Ground Bond depending on whether the inverter/charger is connected to shorepower or not.Then there is the AC ground. Shore power probably ties ground to neutral, and it would tie to equipment enclosure. Shouldn't copper connection extend to chassis, so a short from hot to chassis gets back to neutral and ground without going through enclosure sheetmetal?
When not on shore power, does your inverter tie neutral to ground?
Probably battery negative to the chassis is the thing to do. For all I know, an inverter or charge controller could tie battery positive to chassis and leave negative at -12V, -24V, -48V whatever. Not likely, but I would check documentation.I'm struggling to follow the logic here, I don't see these as separate questions, I think they are very much related.
If you bond your equipment to chassis-ground but don't bond chassis-ground to the source (battery negative in this case) you have not given current an alternate path back to the source (which is one of--if not the--main purposes of equipment grounding). Ground (in the context of a fault) is not the destination, it is a convenient alternate return path. At least that is my limited understanding.
AgreedVery good conversation with input from great minds! The only thing I'd restate just to clarify what was said is:
Chassis-Return: using the chassis as a bus for the primary circuit should only be considered for low voltage applications, typically no higher than 24V, due to shock hazard. This is why we never consider it for 120V AC, and are unlikely to do it with PV circuits. The commonly discussed automobile case is 12V, which is clearly low voltage.
I don't think we are on the same page here. I use and understand Chassis-Ground to mean Chassis-As-Ground (such as in a non-grid/non-earth connected vehicle based system), not to mean what I think you are referring to (connecting the chassis of a piece of equipment to ground via the grounding/bonding system). This I believe would be considered an EGC ("Equipment Ground Conductor").Chassis-Ground: connecting the chassis to earth ground is commonly a good idea independent of voltage. You are providing a path for static discharge and making it easier to install ground fault detection because you now have access to ground at various locations where you might want to install a ground-fault based breaker, a breaker that will open (disconnect) the primary circuit if current is detected between the ground and a primary conductor.
That's a very useful document.Since I posted here last, I have discovered a good grounding resource. It is a difficult subject, many things to consider code wise.
Here it is. Then Mobile grounding section would apply, but you should read all grounding section types to fully understand the correct grounding requirements.
(PS, you need to select the download button, top right, to view and save the pdf file)
Grounding Made simpler - Part 4: Mobile systems.
To get the paper, click on the orange button at the top of the screen. The subject of grounding is a complex, multifaceted subject, that is often treated as an after-thought but needs to be considered from the beginning of the design and build...diysolarforum.com