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24v GROUNDING HELP and overall critique

The inverter chassis if they have ground points, they must be grounded to chassis, and IF ANY APPLIANCES ARE POWERED OUTSIDE THE VEHICLE the chassis must be grounded to earth.

You mean drive a stake into the ground and bond the chassis to the dirt?
 
Don't over think this. It is a vehicle electric system. 24 volts DC. There is no code. There are good engineering practices. The whole chassis can be the DC negative, depending on how "solid" the construction. ie; One solid piece of metal better than welded sections better than bolted pieces. I would like to know more about "ground loops" as I don't think there is any possibility in this scenario. It is best to have high ampere and critical devices return negative to the battery or negative buss bar using cable. But no danger if they also connect to chassis. Connecting chassis direct from battery terminal is fine but you by-pass the battery monitor shunt if you have one. I have run my uni-body van with solar, battery, inverter and fans, lights and what else with multiple negative connections to chassis as well as case "grounding lugs" to the chassis. I have experienced no problems whatsoever. The body just becomes one big DC negative reference. I think that information is for an earth tied system not a dc vehicle. If you have "shore" power plug in, then you must be sure the ac circuit grounding wire. usually green or bare, is tied back to the grounding at the mains panel. Often there is failure in camp grounds.
 
Joey. see my last few sentences about ac circuit grounding. If not connected to mains the inverter uses its case as reference ground. So the chassis. No more danger without ground stake, that will not meet code anyway.
 
I had issues understanding the use of "ground" when I was starting out as well. I managed to understand it a lot better when I worked this out...

As some others have pointed out you need to think of the Voltages (12V, 24V etc) as being based upon a reference, which is 0V.

Imagine you are standing on a flat surface, the floor. There are three ladders; red, green, and blue, leaning against a nearby wall. The red ladder has 24 rungs (24V), the green ladder has 24 rungs (24V), and the blue ladder has 12 rungs (12V).

However, the green ladder (24V) is not actually standing on the floor like the red ladder (24V). It is standing on a step which raises it 1 rung above the floor. This means that, while it is still 24 rungs (24V), it is potentially 1 rung higher when compared to the red ladder using the floor as the reference point.

Both the floor and the step are the starting points (0V) for their respective ladders so they each only go 24 rungs (24V) high. But, because the green ladder starting point (0V) is 1 rung (1V) higher than the red ladder, if you tried to step directly across from the top of one to the top of the other there would be a problem. If you step from the red ladder 24th rung (24V) to the green ladder you'd end up at the 23rd rung (23V). In the other direction, from the green ladder to the red ladder, you'd end up at a point where a 25th rung (25V) would be, but there isn't one, so you'd fall down 1 rung to the red ladder's 24th rung (24V).

The same issue occurs when you consider the blue ladder with 12 rungs (12V) and realise it is sitting on a step that is 2 rungs (2V) higher than the floor. If you step from the blue ladder 12th rung (12V) to the red ladder you'd end up on its 14th rung (14V)!

Grounding your system to the chassis is the equivalent of forcing every single ladder, whether it has the same number of rungs or not, to start on the floor. So, your ladders will all start at the same point (0V) and all the rungs count up from there.
 
So here are my questions:
1. If grounded to the vehicle chassis, being that this system is 24v and the vehicle is 12v, will this difference in voltage lead to any issues?

All the ladders now start at the same place.

2. Is there a difference in grounding to the chassis vs grounding to somewhere more convenient on the body?

The key with this is that your ground connection point needs to have a nice clear path all the way to your reference point. Also, if you ground every single thing at its location in the vehicle then you'll need to be checking a lot of different places (many wont be easy to access) should there be a fault. The best way to solve this is to bring your negative cables back to your negative bus bar and then run a single ground connection to the chassis from there. One ground = one check when there is a fault.

3. If I do ground to the chassis, can the ground cable run off of the negative bus bar?

As above.

4. If the inverter and charge controller need to also be grounded as per their instructions, should those wires run back to the negative bus bar (which would run to the chassis), should they run to a close spot on the body of the vehicle, or should there be an entirely separate ground bus bar?

Best to to check with the manufacturer.

4. Do ground wires need to be solid wire, and what is the appropriate size for chassis, inverter, and charge controller wires?

*ALL* cable used in a vehicle should be stranded. Vehicle manufacturers use it for good reasons. Solid copper does not cope with vibration and movement very well. Over time it work hardens, becomes brittle, and eventually just breaks. Sure, it can take a while (depending on how much vibration the cable is subjected to), but it does happen. Also, stranded is far more flexible so wont cause as many headaches when you're pulling it through the nooks and crannies and around the corners you will when wiring up your vehicle.

5. Can/should the solar panel frames be grounded straight to the body somewhere on the roof?

I've seen examples of both but never seen a definitive reason why I think it is essential. Generally I guess it shouldn't cost a lot to add a ground to the solar module frames so if you can then there's no reason why not to? I'm happy to be corrected though as I just don't know for certain one way or the other.

I have seen people doing it for lightning protection though? But again, not sure whether it's absolutely necessary.

6. Some people recommend not grounding to the vehicle chassis/body at all, citing the discrepancy between the vehicle's power and the sensitive components is a solar system. Is this insane and if not, how should protection be implemented?

I've heard of situations where people have fried their house electrics because they jump-started the vehicle battery. I would suggest installing a way to isolate the electrics of any system before jump-starting or doing anything with the potential to flood a lot of voltage or current into either of them.

I recall their was a YT video by Kinging It where they had roadside assistance come out and jump their bus and it fried their house electrics. They didn't go into detail why that happened but did mention they hadn't isolated the house from the vehicle beforehand.
 
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edit: damnit.. I always comment before checking to make sure there are no further comments below what I am responding too, if anything I said has already been addressed skip over it

Ok...

“ground” means SOOOOO many things...

ground or earthing also is for atmospheric dissipation of static, and lightning...

Vehicle batteries get “grounded” to chassis because wire is expensive, and the chassis is there anyway.

Lets not go there, it just muddies the waters, I wish the car people of yesteryear had never started calling that 'grounded' I get how it started but it has made terminology soo much less clear. Chassis-return (using the chassis as the negative wiring) and Chassis-ground (using chassis as a stand-in for true earth-ground) are much clearer terms. I believe neither OP nor I are talking about chassis return, so the conversation will be simple if we don't go there.

On an inverter bank battery, unless you use the chassis for device current path, I don’t see the need for grounding it... and it could create a dangerous shock hazard with voltages above 24V...

As far as I know it is recommended by nearly all reputable inverter manufacturers to bond the inverter chassis to the grounding/bonding system.

I try to use “bond” instead, as it is less confusing. bonding metal parts to provide a fault path. Allows damaged systems to trip breakers. Needs to be unbroken continuous path to current source.

We are on the same page here, mostly
Equipment ground, or equipment ground conductor/wire, is the term I tend to use in this context, but bond conveys a similar concept I think. The main distinction being bonding and equipment grounding = connecting the not-normally-current-carrying parts of the system to one another, and to the system grounding point (the 1 point where an actual connection between the grounded conductor (DC negative, AC neutral) and Earth-ground or its stand-in (i.e. Chassis-ground) is made). Are we on the same page here?

The inverter chassis if they have ground points, they must be grounded to chassis, and IF ANY APPLIANCES ARE POWERED OUTSIDE THE VEHICLE the chassis must be grounded to earth.

I don't quite follow this, can you explain or give a link or search term?
I know that if the power source is outside the vehicle, there needs to be a single ground path back to that source (this is why UL458 inverters are important), but I did not realize this applied to loads, and would like to understand why.

remember, the marine codes don’t take this aspect into consideration much... water IS EARTHED, and it’s hard to avoid that path... RV... not so much.

Good point, I wish more was available on RV grounding, its really hard to find clear info or reputable information.
 
Disclaim. If there is a shared generator that should be thought of as a "mains supply" the same as Con Ed Cosmic Demonic Power Company. The only time you need an true earth ground is if connected to the mains power. Then it must only be at the main power entry point ie; meter box. You do not have any worry about your inverter in your vehicle powering any device inside or outside the vehicle. You can get shocked the same if earth rod ground or not earth rod ground. You only need an earth rod ground for mains supply and then only at the meter.
 
Don't over think this. It is a vehicle electric system. 24 volts DC. There is no code.

I'm not sure this is actually true. Are you? There is no code inspection, but there are various relevant codes. The significance of which might become very important in the case of an insurance claim for instance (and of course just general safety). It may be that owner-modifiers are exempt, so long as they were not negligent (I have no idea), and/or can demonstrate they tried to follow code (again no idea), but I wouldn't count on it personally without explicit knowledge that that is the case. And code compliance aside, I think its important to try to design things as safely and logically as possible (one of the reasons I like referring to marine standards / ABYC-- I think they do a more than half decent job of a DIY friendly standard).

As to using the chassis as DC negative, i've heard (and this is hearsay not first hand info) that even modern cars have moved away from the practice of chassis-return for the electronics.
 

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  • magnum-msh-rv-grounding.pdf
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  • evo-grounding.pdf
    3.8 MB · Views: 8
  • VFX-RV-Grounding+wiring.pdf
    8 MB · Views: 10
I had issues understanding the use of "ground" when I was starting out as well. I managed to understand it a lot better when I worked this out...

As some others have pointed out you need to think of the Voltages (12V, 24V etc) as being based upon a reference, which is 0V.

Imagine you are standing on a flat surface, the floor. There are three ladders; red, green, and blue, leaning against a nearby wall. The red ladder has 24 rungs (24V), the green ladder has 24 rungs (24V), and the blue ladder has 12 rungs (12V).

However, the green ladder (24V) is not actually standing on the floor like the red ladder (24V). It is standing on a step which raises it 1 rung above the floor. This means that, while it is still 24 rungs (24V), it is potentially 1 rung higher when compared to the red ladder using the floor as the reference point.

Both the floor and the step are the starting points (0V) for their respective ladders so they each only go 24 rungs (24V) high. But, because the green ladder starting point (0V) is 1 rung (1V) higher than the red ladder, if you tried to step directly across from the top of one to the top of the other there would be a problem. If you step from the red ladder 24th rung (24V) to the green ladder you'd end up at the 23rd rung (23V). In the other direction, from the green ladder to the red ladder, you'd end up at a point where a 25th rung (25V) would be, but there isn't one, so you'd fall down 1 rung to the red ladder's 24th rung (24V).

The same issue occurs when you consider the blue ladder with 12 rungs (12V) and realise it is sitting on a step that is 2 rungs (2V) higher than the floor. If you step from the blue ladder 12th rung (12V) to the red ladder you'd end up on its 14th rung (14V)!

Grounding your system to the chassis is the equivalent of forcing every single ladder, whether it has the same number of rungs or not, to start on the floor. So, your ladders will all start at the same point (0V) and all the rungs count up from there.
Thank you for that analogy, that really helps in wrapping my head around the concept.

The inverter chassis if they have ground points, they must be grounded to chassis, and IF ANY APPLIANCES ARE POWERED OUTSIDE THE VEHICLE the chassis must be grounded to earth.
I also would like to understand this better - you replied that an actual stake in the ground should be bonded to the vehicle chassis if we're going to work with power tools off the inverter while outside the vehicle. I absolutely intend on doing this. Where does the danger lie in this situation?

I'm starting to get a more clear path forward here: I'm going to follow the diagram in my Outback controller and have a dedicated ground bus bar, have the inverter and controller ground wires come back to this bus bar, and connect the bus bar to the vehicle chassis as well as the negative bus bar. I wanted the vehicle chassis connection to go straight to my lowest battery's negative terminal, but then I read in another manual specifically NOT to do that. The manual is from a Magnum MS series converter posted by RandyP in the post that Dzl perviously linked to here. It is very informative and thorough with installation instructions. 64-0007-12-04-MS-Manual.pdf
Here's the excerpt:
Screenshot (8).png

Based on that I will have to buy some more 2/0 wire since I don't have quite enough to reach up to where I'll put the ground bus bar. Apparently the ground wires coming out of the inverter and controller going to the ground bus can be smaller (my inverter manual says 14AWG or larger, controller doesn't spec), I need to figure out what makes sense for those wire sizes.
I'll re-sketch this out to post later.
 

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  • 64-0007-12-04-MS-Manual.pdf
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DC Grounding
The inverter/charger should always be connected to a permanent, grounded wiring system. For the majority of installations, the negative battery conductor (black wire) is bonded to the vehicle's safety-grounding conductor (green wire) at only one point in the system. The size for the conductor is usually based on the size of the largest conductor in the DC system. DO NOT connect the battery negative (-) cable to the vehicle's safety ground. Connect it only to the inverter's negative battery terminal. If there are any non-factory installed DC appliances on board the vehicle, DO NOT ground them at the safety ground. Ground them only at the negative bus of the DC load center (as applicable).

I am struggling to interpret this guidance, and also cannot find that specific language in the newer (2020) version of the Magnum MS manual (for the RV specific inverter series MSH3012RV).

How would you interpret the guidance from the Magnum manual you referenced above? How do you think they are defining 'vehicle safety ground'?
Do you interpret this advice as basically saying, ground only at one point, and do so at the DC negative bus/DC load center?

I'm struggling to reconcile the guidance written above, with the example diagram from the manual:
Screenshot_2020-09-13 64-0089 B Owners Manual, MSH3012RV Series indd - 64-0089 B Owners Manual...png

The text (of the older 2004 version) of the manual states:

DO NOT connect the battery negative (-) cable to the vehicle's safety ground. Connect it only to the inverter's negative battery terminal. If there are any non-factory installed DC appliances on board the vehicle, DO NOT ground them at the safety ground. Ground them only at the negative bus of the DC load center (as applicable).

But the image above shows B- going to the DC load center, the inverter, and the ground bus.

Am I misunderstanding the meaning of the disclaimer from the old manual? Or could it be outdated or maybe model specific?
 
I took the " vehicle's safety ground" to mean the connection to the vehicle chassis...

and " For the majority of installations, the negative battery conductor (black wire) is bonded to the vehicle's safety-grounding conductor (green wire) at only one point in the system" to mean that the vehicle chassis connection happens only once, i.e. not connecting to chassis separately for inverter, controller, and batteries, but that they should all come to one point to connect. Upon re-reading I see how that's more of just my interpretation and the text is actually kind of confusing.

And now I'm confused a bit further. The example diagram you just showed which I also previously referenced, shows a nice neat delineation between AC, DC, and Grounding systems. The jumper (SBJ) is going from the negative battery terminal to the ground bus bar, which goes to vehicle chassis. In my Outback controller diagram, the jumper is from the negative bus bar to the ground bus bar...which seems more in line with what the 2004 Magnum manual was saying when it stated " DO NOT connect the battery negative (-) cable to the vehicle's safety ground.", even though they're all connected anyway. Now I'm still struggling to understand what difference it makes whether your one-point connection to the vehicle chassis happens from ground bus bar or or the negative bus bar or the negative battery terminal.

Now, to further confuse matters, on page 13 of the 2020 Magnum manual, figure 2-4 shows the ground to vehicle chassis coming straight off the negative bus bar, and the inverter equipment ground connection going to a terminal with a ground symbol. No ground bus in sight. Why is this different than figure 2-12? ?‍♂️
Screenshot (9).png
 
edit: damnit.. I always comment before checking to make sure there are no further comments below what I am responding too, if anything I said has already been addressed skip over it



Lets not go there, it just muddies the waters, I wish the car people of yesteryear had never started calling that 'grounded' I get how it started but it has made terminology soo much less clear. Chassis-return (using the chassis as the negative wiring) and Chassis-ground (using chassis as a stand-in for true earth-ground) are much clearer terms. I believe neither OP nor I are talking about chassis return, so the conversation will be simple if we don't go there.



As far as I know it is recommended by nearly all reputable inverter manufacturers to bond the inverter chassis to the grounding/bonding system.



We are on the same page here, mostly
Equipment ground, or equipment ground conductor/wire, is the term I tend to use in this context, but bond conveys a similar concept I think. The main distinction being bonding and equipment grounding = connecting the not-normally-current-carrying parts of the system to one another, and to the system grounding point (the 1 point where an actual connection between the grounded conductor (DC negative, AC neutral) and Earth-ground or its stand-in (i.e. Chassis-ground) is made). Are we on the same page here?



I don't quite follow this, can you explain or give a link or search term?
I know that if the power source is outside the vehicle, there needs to be a single ground path back to that source (this is why UL458 inverters are important), but I did not realize this applied to loads, and would like to understand why.



Good point, I wish more was available on RV grounding, its really hard to find clear info or reputable information.
I see why you chopped up the post for responding, but ya omitted some info I used, and missed a step.
As I think I said in the post, he INVERTER chassis needs grounding if provisions are present, but the BATTERY needn’t be unless loads are passed through the chassis, especially if the voltage is over 24V...
 
The inverter chassis if they have ground points, they must be grounded to chassis, and IF ANY APPLIANCES ARE POWERED OUTSIDE THE VEHICLE the chassis must be grounded to earth.

I guess the reason is that if I am using a power tool outside the vehicle and it shorts for some reason, then I become the path to ground since the current has nowhere else to go? But if I am using the power tool inside the vehicle, the vehicle is already isolated from earth ground due to the tires. Is this correct?

I remember asking about this awhile back and you suggested the way around this was to use a 1:1 isolation transformer for a portable DIY like the EcoFlow. I have also seen inverters with isolation transformers built in on alibaba....but I don't trust those, I don't know anything about them.
 
I guess the reason is that if I am using a power tool outside the vehicle and it shorts for some reason, then I become the path to ground since the current has nowhere else to go? But if I am using the power tool inside the vehicle, the vehicle is already isolated from earth ground due to the tires. Is this correct?

I remember asking about this awhile back and you suggested the way around this was to use a 1:1 isolation transformer for a portable DIY like the EcoFlow. I have also seen inverters with isolation transformers built in on alibaba....but I don't trust those, I don't know anything about them.
Current goes to it polar opposite.
 
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I took the "vehicle's safety ground" to mean the connection to the vehicle chassis...

and " For the majority of installations, the negative battery conductor (black wire) is bonded to the vehicle's safety-grounding conductor (green wire) at only one point in the system" to mean that the vehicle chassis connection happens only once, i.e. not connecting to chassis separately for inverter, controller, and batteries, but that they should all come to one point to connect. Upon re-reading I see how that's more of just my interpretation and the text is actually kind of confusing.

This all seems reasonable, but I can't arrive at that conclusion from reading the text.

Actually, on second thought, if we assume "vehicle safety ground" refers to what the diagram calls the "grounding electrode" (vehicle chassis), and we don't focus too hard on the particular wording of that paragraph. We could maybe interpret the advice as a sloppily worded attempt at saying not to connect everything directly to chassis-ground (which is how you read it I think, and inline with the picture, and my current understanding), and connect to a ground bus (as pictured) which is then connected to chassis-ground. I can't say that with any confidence though, and never wouldve interpreted the paragraph tha way without the schematic from later versions.

Based on the fact that the paragraph has been removed from later version, and the schematic has been added. For the sake of my sanity and clarity, I'm going to ignore the paragraph for now and try to follow what later versions recommend.

Now I'm still struggling to understand what difference it makes whether your one-point connection to the vehicle chassis happens from ground bus bar or or the negative bus bar or the negative battery terminal.

I still think this is functionally the same thing. A busbar is a flat piece of copper. Regardless of whether you have one flat piece of copper with both negative and equipment ground connections, or you have two pieces of flat copper called 'negative' and 'grounding' busbars, connected by a round piece of copper we call wire, the outcome should be conceptually the same, I think. Just a little tidier in the latter example.

Now, to further confuse matters, on page 13 of the 2020 Magnum manual, figure 2-4 shows the ground to vehicle chassis coming straight off the negative bus bar, and the inverter equipment ground connection going to a terminal with a ground symbol. No ground bus in sight. Why is this different than figure 2-12? ?‍♂️
View attachment 22660

Yeah that does further confuse things. :confused: I can't make much sense of that second image.
 
Current goes to it polar opposite.

Which in the case of an AC appliance being powered off a battery bank through an inverter would be the battery negative right?
I believe the situation would be the same if it were the SCC supplying the power, just substitute SCC negative for battery negative.

I guess the reason is that if I am using a power tool outside the vehicle and it shorts for some reason, then I become the path to ground since the current has nowhere else to go? But if I am using the power tool inside the vehicle, the vehicle is already isolated from earth ground due to the tires. Is this correct?

I see what you are saying, but this is not how I understand it to be. Because:
1. Current does have another lower resistance path to take, the ground wire (connecting your appliance back to the inverter, and the inverter back to the power source (your battery bank).
2. Current wants to flow back to the source (and/or to lower potential), earth-ground is a convenient path to get back to the source if we are talking about the grid (or anything off-grid that is grounded to earth). But in this case we are talking about a vehicle, isolated from earth-ground, the convenient path back to source (the battery bank) if there is a short is the grounding system and/or chassis-ground.

The advantage I see to bonding chassis ground to earth ground via a grounding rod, is that it will equalize voltage/electrical potential between chassis, earth, and neutral/negative. But I cant quite grasp why or in what particular situations that would be important. I'm in well over my head with the complexities of vehicle grounding, so I may well be misunderstanding something important.


I see why you chopped up the post for responding, but ya omitted some info I used, and missed a step.
As I think I said in the post, he INVERTER chassis needs grounding if provisions are present, but the BATTERY needn’t be unless loads are passed through the chassis, especially if the voltage is over 24V...

Apologies if I misinterpreted something you wrote, I'll go back and reread your comment.
 
I'm in well over my head with the complexities of vehicle grounding, so I may well be misunderstanding something important.

As am I.....that's why I am asking and I know you are too.

1. Current does have another lower resistance path to take, the ground wire (connecting your appliance back to the inverter, and the inverter back to the power source (your battery bank).
2. Current wants to flow back to the source (and/or to lower potential), earth-ground is a convenient path to get back to the source if we are talking about the grid (or anything off-grid that is grounded to earth). But in this case we are talking about a vehicle, isolated from earth-ground, the convenient path back to source (the battery bank) if there is a short is the grounding system and/or chassis-ground.

I understand what you are saying too. My thinking is if operating a power tool outside the vehicle and there is a short, then I also make a good ground path. I don't know which way the current would flow. Would all of it go back to vehicle ground, would all of it go through me, or both? And what would happen if I had on rubber boots or shoes.

I think @Supervstech had a reason for recommending the vehicle needs to be grounded to earth if using appliances outside the vehicle. I would like some clarification on this so we can all understand the reason.
 
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I understand what you are saying too. My thinking is if operating a power tool outside the vehicle and there is a short, then I also make a good ground path. I don't know which way the current would flow. Would all of it go back to vehicle ground, would all of it go through me, or both? And what would happen if I had on rubber boots or shoes.

I think to some degree you are possibly misunderstanding the nature of 'ground' and of current. As I understand it, current flows to 'ground' in an earth-grounded system because the power sources are also earth-grounded so ground offers a path back to the power source.

In a mobile system, the power sources (excluding shorepower) are not earth-grounded, so earth-ground does not offer a path back to source. In the absence of a path back to source, maybe current will flow anywhere that is at lower potential(?) if possible, (I'm a little fuzzy on this). However in this scenario, the green wire in the appliance cord, offers a convenient low resistance path back to source, with thousands of times lower resistance than the human body and an actual path back to source. So I don't understand why this situation would be inherently more risky, even if a short occured.

30ft of 14awg extension cord = 0.075 Ohms
The human body is between 500 and 100,000 Ohms

I think @Supervstech had a reason for recommending the vehicle needs to be grounded to earth if using appliances outside the vehicle. I would like some clarification on this so we can all understand the reason.

I think so too, and I hope to understand them as well, and understand why my thinking is wrong if it is in fact wrong.

If you want to understand my thinking or learn more about grounding, the Mike Holt videos on youtube are where I have got a lot of my understanding from (He is an Electrician, and NEC code instructor and teacher). RSD Academy has a good video on grounding as well.
 
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