Mutiple Chassis DC Negative / (ground) Connections?

[df_2112]

I am in the grunt phase of troubleshooting phase on the install I have going in another thread. The 24V is posing a few challenges I hadn't anticipated and I will outline when I update the post. The question I have at the moment is in regards to using the OEM chassis ground connections. I have a new 1/0 main 'ground' coming from the battery BUS that I installed. At two other sites I re-used the ground up near the tongue where the old batteries were located and just ran wires from my converter to the studs where they were connected. Also behind the panel in the coach where the DC fuses are distributed there is another negative lead that goes from the panel to a bar that catches all of the light circuit returns. That bar is in turn grounded to the frame.

Is there a good reason that I cannot have 3 separate chassis ground connections on the DC side? That is the way they did it from the factory so I am guessing it is reasonable to leave them. I could also isolate them from the frame and only have the one large ground that I installed. Thanks for any input. Can post pics as needed..

[MoonShadow_1911]

I am in the grunt phase of troubleshooting phase on the install I have going in another thread. The 24V is posing a few challenges I hadn't anticipated and I will outline when I update the post. The question I have at the moment is in regards to using the OEM chassis ground connections. I have a new 1/0 main 'ground' coming from the battery BUS that I installed. At two other sites I re-used the ground up near the tongue where the old batteries were located and just ran wires from my converter to the studs where they were connected. Also behind the panel in the coach where the DC fuses are distributed there is another negative lead that goes from the panel to a bar that catches all of the light circuit returns. That bar is in turn grounded to the frame.

Is there a good reason that I cannot have 3 separate chassis ground connections on the DC side? That is the way they did it from the factory so I am guessing it is reasonable to leave them. I could also isolate them from the frame and only have the one large ground that I installed. Thanks for any input. Can post pics as needed..

DC circuit best practice is single point ground. Personally, I would reconfigure everything to a single point ground.

With multiple ground points, you can encounter a ground loop, which can cause DC "stuff" to do wonky things. In an extreme case, it is possible to energize the frame.

Yes, manufactures do it but, it is not best practice and can introduce difficult-to-troubleshoot issues.

Mark & Mary. Currently hailing from New Mexico and going full time in August 2022.
Current coach: 2021 Grand Design Reflection 320MKS
Current Rig: 2019 Ford F350 SD Crew Cab, w/8' box, Lariat, SRW, 6.7l Diesel

[Scott'n'Wendy]

Can't say I agree with MoonShadow on this one. With VAC you don't want the neutral side grounded at more than one point, but with Auto/RV VDC there are always multiple -ve to frame connections. On autos, the frame is treated as a big -ve wire.
IMO, you can attach -ve to the frame anywhere you want with no issue.

[df_2112]

I am guessing that hoping for a 'consensus' may be the best approach here. I am definitely no electrician or electrical engineer or anything of the like, as such I haven't obtained access to the NEC literature for how this should work. In searching a number of forums and threads there are a few things that may contribute so I will start a list.

ITEM 1: Under no circumstances should the AC system and the DC system share a ground or neutral! This can or more likely will lead to the 'hot skin' issue and is under no circumstances a healthy approach.

As for the multiple grounds/bonds etc.

ITEM 2: It seems to me that the factory wiring is more of a 'bonding' of the negatives rather than 'grounding.' This may be semantics but it also has helped me search for additional materials/posts that address the item. Not trying to reinvent the wheel just gather more info.

INFO: https://www.youtube.com/watch?v=B48BUZLomrA
General video on DC grounding. at around 1:33 He refers to the NEC and the voltage of the system. Anything above 50V DC has different requirements per the NEC. He goes on to say that in systems less than 24V the requirements are more relaxed but 'best practice' would be to follow the higher voltage codes.

ITEM 3: According to the info above any system less than 50V doesn't have a grounding requirement but doing so would be a good idea. He makes a few points that might be relevant here and maybe my interpretation is askew but in higher voltage systems having two 'paths' would not be allowed.

I am not trying to take one side or the other here. The one thing that seems to be clear is that there seems to be plenty of gray area. I guess I would hope to have a healthy discussion between the current practices of the manufacturers of our rigs and those that have an interest in upgrades or at least compile more information. As we add a lot more 'power' to our systems we will possibly run up against some of these barriers or have a greater requirement best practices. I am leaning towards taking the extra time to isolate the returns on this build mostly because I am running a 24V system and will have up to 30V in the central part of the wiring and >50V coming in from the solar panels to the MPPTs at peak. At the same time all of my branch circuits and panel supply etc leave from a 24V/12V converter before branching out into the trailer.

[powerscol]

Denniis
The term ground in 12V is a misstatement. It is the negative return path. you will be fine with multiple ones as long as the negative line gauge is equal to or larger than the positive feed. If not the negative side can overheat in a current overload just like the positive side.

Reserve the term ground to AC circuit's that have a true ground going to earth - Like through the power cord to the source box that has the copper rod driven in the ground somewhere in the circuit.

On edit
You will find that GD actually does bond the AC ground to the trailer frame. Find the main ground wire (bare copped) in your distribution box and I'll bet you a cup of coffee that you will find it goes to the frame somewhere. I found mine when I pulled the belly fabric. However in no case should the neutral (white AC circuit wires) tie into the frame. Fortunately GD used solid copper wire (romex) on the AC side. There are exceptions though.

[df_2112]

Denniis
The term ground in 12V is a misstatement. It is the negative return path. you will be fine with multiple ones as long as the negative line gauge is equal to or larger than the positive feed. If not the negative side can overheat in a current overload just like the positive side.

Reserve the term ground to AC circuit's that have a true ground going to earth - Like through the power cord to the source box that has the copper rod driven in the ground somewhere in the circuit.

Will see if I can edit the thread title. I am learning as I go on this but getting the terms right is important.

On edit
You will find that GD actually does bond the AC ground to the trailer frame. Find the main ground wire (bare copped) in your distribution box and I'll bet you a cup of coffee that you will find it goes to the frame somewhere. I found mine when I pulled the belly fabric. However in no case should the neutral (white AC circuit wires) tie into the frame. Fortunately GD used solid copper wire (romex) on the AC side. There are exceptions though.

You are correct sir!



Quick photo behind the panel inside the rig. The arrow on the right shows the DC negative return bus. The black wire on the left above the arrow goes back to the negative in the panel. The black wire on the right loops up and dives down to the frame where it is bonded to the frame. The solid copper in the circle on the left ties back to the ground bar on the AC side of the panel and is bonded to the frame at the same point as the DC return. I could barely intermittently see the connection using a mirror (goofy angles) but I ran my hand down the line and can feel the bonding connector for both cables.

I am thinking I will disconnect the black wire on the right on the bar and allow the 4AWG negative cable I have run from the 24/12 converter as the only return from the DC side of the panel.

[powerscol]

Will see if I can edit the thread title. I am learning as I go on this but getting the terms right is important.



You are correct sir!



Quick photo behind the panel inside the rig. The arrow on the right shows the DC negative return bus. The black wire on the left above the arrow goes back to the negative in the panel. The black wire on the right loops up and dives down to the frame where it is bonded to the frame. The solid copper in the circle on the left ties back to the ground bar on the AC side of the panel and is bonded to the frame at the same point as the DC return. I could barely intermittently see the connection using a mirror (goofy angles) but I ran my hand down the line and can feel the bonding connector for both cables.

I am thinking I will disconnect the black wire on the right on the bar and allow the 4AWG negative cable I have run from the 24/12 converter as the only return from the DC side of the panel.

You could do that, but there is no real need. Doing that could lead to other issues. Increasing the run of the negative 12V wiring can lead to excessive voltage drop. Remember the current sees the total length (resistance) of the 12V wire run. I would leave things as is. Your lucky that GD did a nice job. All I would do is check the tightness of each connection and not worry about it.

Now if your installing a heavy draw unit like a Multiplus or inverter that has a large gauge feed wires, it best to have the chassis ground (green screw on frame of multiplus or inverter) be the same gauge as the power feed. This makes sure the power fuse will blow rather than a thin chassis wire, or other unit negative 12V wires from melting in case of n internal short to the multiplus or inverter frame/box. Also theses two negative bond/ chassis ground wires should connect to the frame as far apart as possible. This will help prevent any transient voltage situations. On my unit I tied the negative bond to the far left of my front bay (along with negative side of the battery) and the chassis ground bond wire from all of my solar equipment to the far right of the front bay.

[Jerryr]

DC circuit best practice is single point ground. Personally, I would reconfigure everything to a single point ground.

With multiple ground points, you can encounter a ground loop, which can cause DC "stuff" to do wonky things. In an extreme case, it is possible to energize the frame.

Yes, manufactures do it but, it is not best practice and can introduce difficult-to-troubleshoot issues.

Mark & Mary. Currently hailing from New Mexico and going full time in August 2022.
Current coach: 2021 Grand Design Reflection 320MKS
Current Rig: 2019 Ford F350 SD Crew Cab, w/8' box, Lariat, SRW, 6.7l Diesel

Man, You just woke up some bad memories of hundred of hours troubleshooting buzzing, whining or humming on aircraft audio circuits due to ground loops when multiple grounds were used.

[MoonShadow_1911]

Man, You just woke up some bad memories of hundred of hours troubleshooting buzzing, whining or humming on aircraft audio circuits due to ground loops when multiple grounds were used.

Ummmm, you're welcome? I can't tell you the hours I've spent troubleshooting ground loops in "micro DC" circuits. When I design and build my own circuits, I always have a single point ground. I've got a story where I had a device that was grounded to the bench, and the bench was floating and not grounded. Took me two days to figure that one out!

Mark & Mary. Currently hailing from New Mexico and going full time in August 2022.
Current coach: 2021 Grand Design Reflection 320MKS
Current Rig: 2019 Ford F350 SD Crew Cab, w/8' box, Lariat, SRW, 6.7l Diesel

[SolarPoweredRV]

I am guessing that hoping for a 'consensus' may be the best approach here. I am definitely no electrician or electrical engineer or anything of the like, as such I haven't obtained access to the NEC literature for how this should work. In searching a number of forums and threads there are a few things that may contribute so I will start a list.

ITEM 1: Under no circumstances should the AC system and the DC system share a ground or neutral! This can or more likely will lead to the 'hot skin' issue and is under no circumstances a healthy approach.

As for the multiple grounds/bonds etc.

ITEM 2: It seems to me that the factory wiring is more of a 'bonding' of the negatives rather than 'grounding.' This may be semantics but it also has helped me search for additional materials/posts that address the item. Not trying to reinvent the wheel just gather more info.

INFO: https://www.youtube.com/watch?v=B48BUZLomrA
General video on DC grounding. at around 1:33 He refers to the NEC and the voltage of the system. Anything above 50V DC has different requirements per the NEC. He goes on to say that in systems less than 24V the requirements are more relaxed but 'best practice' would be to follow the higher voltage codes.

ITEM 3: According to the info above any system less than 50V doesn't have a grounding requirement but doing so would be a good idea. He makes a few points that might be relevant here and maybe my interpretation is askew but in higher voltage systems having two 'paths' would not be allowed.

I am not trying to take one side or the other here. The one thing that seems to be clear is that there seems to be plenty of gray area. I guess I would hope to have a healthy discussion between the current practices of the manufacturers of our rigs and those that have an interest in upgrades or at least compile more information. As we add a lot more 'power' to our systems we will possibly run up against some of these barriers or have a greater requirement best practices. I am leaning towards taking the extra time to isolate the returns on this build mostly because I am running a 24V system and will have up to 30V in the central part of the wiring and >50V coming in from the solar panels to the MPPTs at peak. At the same time all of my branch circuits and panel supply etc leave from a 24V/12V converter before branching out into the trailer.

In reading your post regarding the NEC...

I am wondering if the documentation is referring to "Earth Grounding" versus the more common 12v DC practice of using the metal vehicle body as a "return path" to "Negative" terminal on the battery?