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Help me understand how to ground our homemade camp trailer

Tomthumb62

Solar Wizard
Joined
Sep 25, 2022
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Forgive such a basic question. I searched but didn’t find an answer though I’m sure it’s been covered.

Is all I need to do is ground the black bus bar with all the DC side of things to the metal chassis of the trailer? And do the same for the AC side? And both AC and DC can ground to the same point? 12v dc and 120v ac. For shore power, most of the time we’d connect to the grid, but on occasion we might charge from a generator.

Also, I assume the trailer is also grounded to the tow vehicle when coupled but I’m not 100% sure how to test this…does it matter either way?

Grounding has always mystified me, so I’d love if someone could double check me here. Thank you!
 
A "ground" usually means a connection to the earth. Trailers and vehicles are on rubber tires and there is no electrical connection to the earth - e.g. "earth ground" is not possible. Using the chassis as the negative for a 12v system is common for vehicles and trailers but just keep in mind that the negative of a 12v circuit is not the same as a "ground" in the 120v sense. Also, 12v systems are not shock hazards the way 120v can be.

As to grounding 120v... in my trailer's 120v system I have a ground wire connected to sockets and appliances (normal 120v US wiring) but it's routed to the incoming grid connection on the side of the trailer. It's not hooked to the chassis and not connected to the12v system at all. When grid from my home is plugged in to power the trailer this connects my trailer's ground to my home's ground and thus the trailer's 120v system is 'grounded'. At a campsite power box or unknown grid power source coming into you're trailer - it should be grounded but I don't have a way to actually test it.

When a generator is hooked up there is no earth ground unless ones grounds the generator. This is possible but not practical for mobile generators. There is the concept of neutral-ground wire bond option at the generator - yet another topic. Personally, I just use my generators (Champion and Honda) as they came from the factory and there is no earth ground.

Bottom line,
- I wouldn't mix 120v and 12v systems - e.g. I wouldn't hook any of the 120v wires or the 120v ground wire to the chassis.
- Agree that the external grid supply (home or campsite or generator) is the right place to think about 120v grounding.

However, I'm not an expert and just sharing what I did to help clarify some talking points. There are true experts on this forum and I'm hoping you'll get some expert advice. It's an interesting topic to me as well.
 
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A "ground" usually means a connection to the earth. Trailers and vehicles are on rubber tires and there is no electrical connection to the earth - e.g. "earth ground" is not possible. Using the chassis as the negative for a 12v system is common for vehicles and trailers but just keep in mind that the negative of a 12v circuit is not the same as a "ground" in the 120v sense. Also, 12v systems are not shock hazards the way 120v can be.

As to grounding 120v... in my trailer's 120v system I have a ground wire connected to sockets and appliances (normal 120v US wiring) but it's routed to the incoming grid connection on the side of the trailer. It's not hooked to the chassis and not connected to the12v system at all. When grid from my home is plugged in to power the trailer this connects my trailer's ground to my home's ground and thus the trailer's 120v system is 'grounded'. At a campsite power box or unknown grid power source coming into you're trailer - it should be grounded but I don't have a way to actually test it.

When a generator is hooked up there is no earth ground unless ones grounds the generator. This is possible but not practical for mobile generators. There is the concept of neutral-ground wire bond option at the generator - yet another topic. Personally, I just use my generators (Champion and Honda) as they came from the factory and there is no earth ground.

Bottom line,
- I wouldn't mix 120v and 12v systems - e.g. I wouldn't hook any of the 120v wires or the 120v ground wire to the chassis.
- Agree that the external grid supply (home or campsite or generator) is the right place to think about 120v grounding.

However, I'm not an expert and just sharing what I did to help clarify some talking points. There are true experts on this forum and I'm hoping you'll get some expert advice. It's an interesting topic to me as well.
Thank you, that’s really helpful to hear. I will just skip the grounding point altogether. Or perhaps I will wire it up and should we boondock in a place for more than a few days, I could pound a rod into the ground that’s connected to the trailer chassis. That said, would it be okay to ground the inverter (through the dedicated ground screw) to the 12v system/chassis? Meaning, I’m not sure if the ground screw is for the AC or DC side of the inverter. It’s a Victron 12/1200.

I thought I had read that it’s fine to “ground” the AC and DC systems together, as in a marine or mobile environment, but it makes me nervous. And your recommendation to not do that just confirms it. Thanks!
 
Thank you, that’s really helpful to hear. I will just skip the grounding point altogether. Or perhaps I will wire it up and should we boondock in a place for more than a few days, I could pound a rod into the ground that’s connected to the trailer chassis.
The trailer-vehicle chassis-metal / 12v does not need a ground as 12v is not a shock hazard.

That said, would it be okay to ground the inverter (through the dedicated ground screw) to the 12v system/chassis? Meaning, I’m not sure if the ground screw is for the AC or DC side of the inverter. It’s a Victron 12/1200.
For an inverter that produces 120v - I would assume the ground lug is for the 120v output (not the 12v input). As I said above, 12v is not a shock hazard like 120v. If you were to connect the 120v ground to the chassis, you could potentially create a situation where you lean on a fender (or metal side of a trailer) or open a door to the vehicle and you're feet on the ground complete the circuit and you could get shocked/hurt.

I thought I had read that it’s fine to “ground” the AC and DC systems together, as in a marine or mobile environment, but it makes me nervous. And your recommendation to not do that just confirms it. Thanks!
You can check with Victron - I understand they have good support and I'd take that over anything I've written here. Meanwhile, I wouldn't connect the inverter ground to the chassis or metal framework of trailer or vehicle. Connect that ground to the 120v wiring ground. Just keep 120v and 12v completely separate.
 
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Yes the battery negative should be bonded to the frame.

Same as the ground connection of the 120v system if the inverter is permanently installed to power a distribution panel. This is only the ground wire NOT the hot or neutral. Not all inverters will like the battery negative attached to the ground. This type of inverter should remain independent and plug items in direct only. Inverters installed should also have a chassis ground connection for the outer case to have an independent connection to the vehicle frame.

The utility power connection will be the only time the ground and frame is actually connected to an earth ground. The utility cord to the generator will plug in direct. Do not create an earth ground for the generator.

This is how every RV is built and meets electric code.
 
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