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Old 04-27-2017, 11:08 AM   #1
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Should I bond DC negative with AC ground to bus body?

I've spent some time researching on this forum and others about electrical design but I've been unable to find a consensus on how to properly wire up grounds for a system with parallel AC and DC circuits.

I want to avoid the "hot skin" condition as well as simplify the grounding of my small set of DC devices (LED lights, roof hatch fans, and the fresh water pump). I plan to use marine stranded wiring for the AC circuits.

My proposal would be to ground the DC devices to the body where they are mounted to simplify the number of wires I have to run (hots only) and grounding the 12V power supply to the body as well. Each AC circuit would have a dedicated ground wire all coming back to the power distribution panel which itself would be grounded to the bus body too. AC neutral would remain floating.

Do you guys have any thoughts on my grounding proposal? If this has already been answered I apologize and would appreciate a link to the previous thread(s).
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Old 04-27-2017, 11:34 AM   #2
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Just found this article that illustrates exactly how I planned to setup my system except I won't have a need for an RF ground.

Getting Grounded the Right Way
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Old 04-27-2017, 12:06 PM   #3
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let me start by saying I'm no electrician.

imo, there are more than one way to skin a cat. your diagram works fine but the batteries share a ground so they live and die together. you want to find a way to isolate your batteries from each other. battery isolator or....

my bus house has a floating 12vdc+- completely separate from the vehicle, but you have to run 2 wires to everything.

the advantage of floating 12vdc+- is that the house won't short across the bus, only to itself. i can touch the hot house lead to the bus and nothing happens since the circuit is not complete.

the on board battery charger is grounded to the ac side and bus chassis, but the house current floats.
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Old 04-27-2017, 12:10 PM   #4
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Thanks for that insight. I'm not sure if it matters or not but I'm not actually planning on using any batteries right away. I'm going to use a power supply that converts AC to DC. Typically I have at least a modest AC hookup where I go and I figured I could always complicate the DC system at a later date by adding batteries.

By choosing to forego actual batteries for now I save the cost of batteries, a charger, and an inverter. These are all things I think I can add easily later if I want to do more off the grid stuff, but I also plan to have a generator too, so I may never need battery only.
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Old 04-27-2017, 02:20 PM   #5
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12v Camping converters are pretty cheap, with battery charger built in.

but imo, if you leave off the battery, you'll only be able to run your 12v loads while the engine runs or you are plugged in. the load will kill you starting battery if used with out assistance. so you are opening up yourself for a problem.

vehicle batteries are tapped out doing what they do for the vehicle. you'll still want to protect your start battery from the house load.
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Old 04-27-2017, 04:31 PM   #6
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I don't plan to interconnect the vehicle battery with the conversion at all unless you mean that it may drain the starting battery simply because they share a common ground. For now I'm fine with only having DC power provided by my AC power supply when I'm connected to shore or the generator.
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Old 04-27-2017, 05:38 PM   #7
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Yes, bond the ac ground to the bus body. The ac ground-neutral bond is a bit more involved: when shore power is used, the shore power should provide a ground-neutral bond and the bus should not. However, when portable power is used (most commonly an inverter or generator) then it's your responsibility to ensure that something somewhere provides that bond for you. There are plenty of inverters and generators that do as built by the factory, but plenty also that don't.

One potential problem with keeping systems floating relative to each other is that sooner or later there'll be some piece of equipment that unwittingly ties them. Just as a quick example, a dc-powered TV might be connected to an external antenna which connects to the bus chassis, or a DVD/game console input or AV receiver output with a 3-wire mains plug might provide a path from the dc ground through the ground of the TV's signal inputs to the grounded antenna or mains-powered gear. It won't necessarily create a safety hazard, or even an immediate failure, but those kinds of "hidden" interconnects are something to keep in mind when intentionally isolating systems.
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Old 04-27-2017, 06:54 PM   #8
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Since I plan to ground both AC and DC together at the body from the beginning I guess we'll see what happens. Good point about the neutral binding. I had read about that. I need to test my generator and if it doesn't I'll wire up a simple plug for that bonding.

Thanks for all the great replies. I'm so glad I found this forum!

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Old 06-04-2018, 11:10 PM   #9
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Quote:
Originally Posted by hatchetman View Post
I don't plan to interconnect the vehicle battery with the conversion at all unless you mean that it may drain the starting battery simply because they share a common ground. For now I'm fine with only having DC power provided by my AC power supply when I'm connected to shore or the generator.
I'm getting ready to start planning our panel and shorepower for our bus. I bought a 100amp panel with a 100 amp main breaker that will act as the switch to cut power from the source. The source will always be 30amp.

I watched videos on how to wire the panel and one of them said the ground and neutral are bonded at the panel. Below you can scroll through this YouTube and see what I mean.

https://youtu.be/DVc_4PtZXPQ

Is this the proper way ? I know the RV parking panels usually are grounded ..what I'm asking is if I have to bond the ground and neutral in my panel as this video says in a house application? I can't understand this part since I'm doing this in a bus not a house. Obviously when using a generator I would need to ground the generator with. A rod for safer use.
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Old 06-05-2018, 05:28 AM   #10
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Quote:
Originally Posted by Rawlings View Post
I'm getting ready to start planning our panel and shorepower for our bus. I bought a 100amp panel with a 100 amp main breaker that will act as the switch to cut power from the source. The source will always be 30amp.

I watched videos on how to wire the panel and one of them said the ground and neutral are bonded at the panel. Below you can scroll through this YouTube and see what I mean.

https://youtu.be/DVc_4PtZXPQ

Is this the proper way ? I know the RV parking panels usually are grounded ..what I'm asking is if I have to bond the ground and neutral in my panel as this video says in a house application? I can't understand this part since I'm doing this in a bus not a house. Obviously when using a generator I would need to ground the generator with. A rod for safer use.
I'm not an electrician so if you are unsure you should consult a professional to be safe. I plan to treat the panel in my bus as a sub-panel meaning that I will keep my ground and neutral separate. I also just plan to ground my generator to the chassis, after all using a grounding rod as I'm traveling down the road to run the air conditioner might get complicated.
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My conversion thread: https://www.skoolie.net/forums/f11/project-huckleberry-17952.html
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