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Old 11-07-2020, 07:31 PM   #41
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Join Date: Sep 2019
Location: Bly Oregon
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Year: 1986
Coachwork: Crown
Chassis: Supercoach
Engine: Cummins 350 big cam
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Hopefully the final answer about ground

An answer as to why some think that folks confuse ground and chassis on motor vehicles is because the industry uses the term ground and schematics of motor vehicles utilize the schematic symbol for ground. Terms like negative ground and positive ground are prevalent. The English were fond of positive ground. I still will wire my bus like a house, meaning neutral will still have a wire, ground (green wire) will have a wire. Of course my electrical panel will be electrically connected to the chassis of the bus through the unistrut I am using to frame the walls. This means that through the electrical panel both neutral and ground (green wire) connect through the shell of the electrical panel. As my bus has a second alternator mounted on the engine that due to its mounting current flow originates from its housing, through the engine block, through a "grounding strap" to the frame of the bus. Thus the DC current flow will pass through the frame to batteries through their negative terminal, and through any device that will conduct electron flow to the positive of batteries that have a negative connection to the chassis. The current flow also returns to the positive terminal of the second alternator. The same operation of current flow occurs with the original Crown bus electrical system, but this electrical system is isolated from the RV electrical system. DC current will flow through the chassis for both RV and bus electrical, but both are still separate, since NO point of RV and Bus electrical have a common positive. Under normal conditions NO AC current will flow through the chassis of the bus. If you for sake of discussion had a power tool that developed a short between the HOT ac wire to the metal enclosure, current will flow to the ground wire (the third round pin of its plug) and cause the circuit breaker to trip. If any one is still confused, try an internet search for wiring of say a 1990 ford f250 wiring diagram. keep looking and you will find a schematic with a ground symbol. The term schematic is a term for a wiring diagram of an electrical or electronic device, such as a tv, radio, phone, etc. An internet search of "transistor radio schematic" should produce the following image:


In that image at the bottom wire is the symbol for ground. A lot of wiring diagrams for motor vehicles have that symbol. To me it is simple. AC ground is a green or bare wire connected in all circuits and in your electrical panel. In DC it is usually the chassis of the vehicle. Not all vehicles have a frame, but all have a chassis. AC ground only conducts with electrical failure (short to enclosure), DC in most vehicles ground /chassis carries current. Don't mix the two and you will be OK.
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Old 11-08-2020, 08:02 AM   #42
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Wow. An old style analog schematic.. with real dedicated parts... Ahhh.. so much more fun then ....

Hi Johan
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Old 11-08-2020, 09:51 AM   #43
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12 volt ground

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Originally Posted by Bpike View Post
My conversion plan consists of a 12v DC system (lighting and water pump) and a 110v AC for fridge, AC, hot water heater, microwave, induction hot plate, and a charger for the batteries. I am initially thinking a separate pair of batteries for the 12v system to keep the bus chassis system separate from the conversion system. Is this foolish, should I just tap into the bus batteries for the 12v, and add a shore charger to it, and be done? Also if I do go separate 12v system, can I use the chassis for ground to keep from running ground wires, any danger here with both 12v systems using a common chassis ground?

I have worked alot in the construction industry and built and race my own drag cars. Over time you will find that ground issues with lights and accessories can reak havoc on your system and mind. If I were to build a schooly I think I would consider running a seperate larger ground wire from one end to the other using that as a common ground. I wire all off my race cars with what I call a two wire system. For every component that has a power wire running to it it has a seperate ground wire either running to a ground block that is connected directly to the battery ground. I have zero issues with my electronics. The other thing to remember is if the ground is not good it will take more amps to run whayever you have turned on. Cost is higher and a little more labor intensive but well worth it in my mind. Just remember to upsize the wire to the ground block if you do this as it will be covering more than one component.
Rust and joints in chassis grounds over time create issues, just what I've found over time.

Good luck in your build!
Popper
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Old 11-09-2020, 01:58 AM   #44
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Quote:
Originally Posted by joeblack5 View Post
Wow. An old style analog schematic.. with real dedicated parts... Ahhh.. so much more fun then ....

Hi Johan
Indeed, there is elegance in such circuits.
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