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Old 09-05-2017, 08:19 PM   #1
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Confusion on AC wiring...

Before you ask... Yes, I've been reading through the electric threads in the tutorial section of the site.

Here's what I can't wrap my head around.

When you aren't hooked up to a shore pedestal but are still running 120 volts, how do you ground the system for safety reasons?

We're planning on having a 12v battery bank and an inverter for off grid use. In this case, the entire system is inside the bus.

I've seen frequent mentions of neutral ground bonding, but don't understand exactly how this works or what it achieves.

I've also read people talking about grounding it to the vehicle, but wouldn't this cause a hot skin type of problem? If not, why not? Also, would this not cause any interference with the bus batteries?

These may seem like profoundly dumb questions to people who understand all this, but I appreciate the help.

In the meantime, I'll keep reading more threads...
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Old 09-05-2017, 08:24 PM   #2
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I also have read thread and watched YouTube. However I have the same issue. I am ready to wire the circuit breaker panel but the ground bus bar is the issue also.

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Old 09-05-2017, 09:44 PM   #3
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I'll let you know if I make sense of it all!
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Old 09-05-2017, 09:59 PM   #4
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reply

Make sure you post what you find out so the rest of us can do it as well!
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Old 09-06-2017, 07:15 AM   #5
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Will do.

This is something...

"NEVER, EVER tie neutral and ground
together, manually, in any installation, period! Neutral is
tied to ground at the source of AC power simply to allow
the ground wire to be an alternate path for return current
during a failure where the hot wire touches the chassis of
a device or vehicle. This is intended to trip the breaker.
However, when neutral is tied to ground in the vehicle,
thereís a voltage potential between the ground plane of
the vehicle, and the ground plane of the electrical grid
connection. If thereís resistance on the ground and neutral
wires, the current will find some other potential path back
to earth ground and that path may be you as you open
the door of your vehicle. This isnít the kind of excitement
you want to experience!"

From this document

http://www.xantrex.com/documents/Tec...-Universal.pdf
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Old 09-06-2017, 07:48 AM   #6
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always have a copy of the NEC ... or pretty current copy. u can learn lots.
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Old 09-06-2017, 10:14 AM   #7
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Okay guys I am dumb, you are saying use a grounding bar and is it okay to attach it to the frame?

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Old 09-06-2017, 10:29 AM   #8
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Originally Posted by IWC Bus View Post
Okay guys I am dumb, you are saying use a grounding bar and is it okay to attach it to the frame?

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Please make sure you tap your network of friends and family and find an electrician to check whatever your wiring. I can appreciate wanting to understand and do the work yourself, just put some trained eyes on your work.

People are reluctant to give specific electrical advice in case someone gets injured or kilt. Or worse- your sine wave flux inverter gets melted.

Post some pictures of your electrical diagram and that may help. List your expected loads and sources.
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Old 09-06-2017, 11:16 AM   #9
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Simple solution:

Stop running AC power in your bus. Use DC instead. DC is easier to understand, and at 12v much much safer. Plus, you won't be spending 1/3 of your power budget doing ac/dc conversions.

My bus runs entirely on 12v DC with the exception of my TV and refrigerator, which connect directly to my inverter.

The only time AC at scale comes out ahead is if you're always tethered to shore power.
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Old 09-06-2017, 11:43 AM   #10
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Ok I am probably wrong... When you run shore power, you basically send the neutral and ground through the wire to the shore power breaker/ground.
You need a physical switch to go to gen power... And the ground goes to the chassis(here is where my memory is fuzzy) and the generator has to somehow have the neutral tied into the chassis. Besides here search Google. There is a pretty detailed explanation on "hot skin" that gives the exact wiring.

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Old 09-06-2017, 01:34 PM   #11
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someone else posted elsewhere

https://skywagonskoolie.wordpress.com/electrical/

* was user: The Rockwood Colony
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Old 09-06-2017, 01:37 PM   #12
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To get accurate information you should really put up some pics of the exact equipment you are using. Just guessing otherwise but most breaker panels have neutral and ground busses to connect your service to and the secondary circuits also.
If you have a genny ground the frame of it with a wire going outside and down to a ground rod which you have to hammer into the ground.
I can really understand the reluctance of advising people who have no clue and won't read on this subject.
Break the whole project down to smaller bits and get those bits right first. You need a service cord to feed the bus. Do it. Then a service panel, mount one where useful.
Put in your lights and receptacles and wire back to the panel with appropriate size wire.
I might not be to clear here but the neutral in the panel connects to the neutral in the service cord only for its grounding.
So, no more comments on this from me unless I see what you have.

John
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Old 09-06-2017, 03:26 PM   #13
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As others have said, much of the detail depends on the specific equipment you want to use. That said, I'll try to offer a few general thoughts that may be useful.

As you recognized, it's important to do something with the ground wire in order for it to be useful as a safety. The specifics of what to do vary depending on circumstances, but once a person gets a good handle on how the safety systems work, it all starts to make sense.

First principle: conductive parts should never be left electrically "floating" -- meaning, having an indeterminate voltage on them. If a conductor isn't intended to supply electric current to a known load then it should be grounded. Imagine a conductor that is expected to be non-energized. A metal hand rail, maybe. If we've "bonded" (connected) it to "ground" potential, then if ever some fault happens and a live wire comes into contact, we'll immediately know about the fault. It'll arc and spark until a circuit breaker trips or a fuse blows. If that hand rail were not bonded to ground then nothing would immediately happen when the live wire came into contact. That hand rail would sit there energized until somebody's grandma came along in her bare feet on the metal stairs and grabbed the hand rail for support (for example). It would be the (last) shock of her life. The rationale for this principle is that if things that should not be energized are grounded, then when a fault happens a protective device (circuit breaker etc) will interrupt. It'll prevent the danger from existing indefinitely. Based on this principle, the bus body should be connected to "ground" for both the ac and the dc systems.

Aaaannd.. I've got to run. I'll try to get back tonight to write more about what "ground" is and why it changes depending on the source of ac power.
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Old 09-06-2017, 04:31 PM   #14
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Like I said, I have been researching this basically non-stop for the last few days. I didn't mention any specific equipment because what I want to understand is specifically the 'theory' behind why and how it works. I think I've finally started to put the pieces together.

A lot of my confusion seems to have originated with what I think is relatively poor terminology when it comes to electric stuff.

This may be a long post, but I'm going to explain my current understanding of how this all works. If any experienced people have the time, I'd really appreciate critiques of this.

Every system is going to have to have power inputs (shore, generator, solar), breakers & fuses, and outputs (where the electric is actually being used). Most of us will also have storage, which in almost all cases will be the 12v battery system.

On the A/C side of things, we've got 3 different types of wire: hot, neutral, and ground.
Despite the fact that most places say the hot wire sends the power and the neutral is the return, this isn't how it's actually working. Since the whole concept of AC is that the current alternates, your hot and neutral wires will rapidly switch between sending and returning your power. The real difference is that the neutral wire is bonded to the ground at the

The ground wire is strictly a return. It connects to metal in the device being powered so that if there is a short in the device, there is a low resistance path back to the breaker box to complete the circuit with more power than designed and trip a breaker and stop power from flowing. This prevents the device from becoming energized and a potential shock hazard.

So now we're safe from short circuits within our appliances.

But what about if a wire becomes exposed through rubbing and begins to energize the bus itself? It is a giant box of metal, after all.

That's where the other version of grounding in an rv comes into play. This is why you see people instructing you to make sure your electrical system is grounded to the frame. Once again, the ground never drives power and when everything is functioning properly, it isn't returning any power either.

I may still be thinking about this wrong, but I actually think the way most people talk about this is backwards. We're basically grounding the frame of the bus to the electric panel, not the other way around. This is where a lot of my original confusion came from. I kept thinking, why would we send the extra power into the bus frame? Why would anyone want to ground to the frame? Then I realized we're not, we're giving unwanted energy that may end up in the bus metal or on the 'skin' a path back to trip breakers and kill the power.

That pretty much covers the grounding that I was curious about (when the AC is created by an inverter from a battery bank, all inside the bus).

Now tear that apart

Edit: I think I have the shore power part of things understood well. Someone above mentioned needing an actual ground bar for your generator. I thought there was a way to achieve safety without actually doing a ground bar in a similar fashion as above (using ground wires to trip circuits and stop the power). Putting a ground bar in everytime you park seems too impractical to be the best option out there. What if you park on concrete without close enough access to ground? What if you are somewhere sandy (sand being a poor conductor)? Again, I have to assume safety can be achieved without these.
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Old 09-06-2017, 05:16 PM   #15
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I have never grounded AC in any mobile environment. Every RV I have ever seen does not ground AC to vehicle frame. My Inverter/ Charger has a ground lug on it to send to frame, as does my generator, but those are not the same as the "ground" on AC branch circuits. I use 3 conductor wire to home run hot, neutral, and grnd for each and every outlet, and device. Those in turn are hooked together at the AC/ DC breaker panel (PD5000). That is fed by a 3 conductor wire to AC output of Inverter/ Charger. So in a sense it is "floating" AC system. If somehow an AC charged wire shorts to the frame of vehicle, the ground LUG from the Inverter/ Charger or Generator(whichever is in use at time) senses the power on the frame and shuts down. This is what is stated in the installation manual, and I have tested it. I used a piece of 12/3 wire from PD5000 breaker branch #1 and touched the hot to the lug on Inverter/ charger. It sparked and shut down. After pressing the 2 reset breakers on my Inverter/ Charger everything was back up...NO DAMAGE WAS DONE. I did the same with the neutral side. So by this test and manual instructions for the AIMS3000PICO Inverter/ Charger the ONLY parts that should be bonded to the frame of vehicle are the little brass lugs on the frame of my Inverter/ Charger, and the one on my generator. The actual breakers in my PD5000 distribution center are only for over current protection of equipment. This is also why I use a surge protector on shore input that protects everything beyond the shore input plug, as there is no way to protect the shore feed prior to the inverter. My recommendation is to NEVER ground AC to a vehicle frame. Only DC. This is how every RV I have ever seen is wired.
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Old 09-06-2017, 07:39 PM   #16
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That makes sense and I think it fits in with / builds on my understanding.

Based on what you're saying, the grounding/bonding to the frame happens at the actual inverter/generator, not after these output the a/c. So they're designed with what would essentially be a breaker inside them that will flip if there is a short in the system. That way they'll immediately shut down if a short occurs, ensuring you don't accidentally walk up to the bus/rv and become an actual ground to the earth when you touch it (hot skin).

Did I get that right?
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Old 09-07-2017, 03:35 PM   #17
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The suggestion to keep the metal body of an RV disconnected from the electrical system ground is unsafe for the reason described earlier: if (when) a fault happens such that a hot wire energizes the body, there needs to exist an intentional circuit or path so that a safety device will trip. If the metal body is left floating then that circuit doesn't exist. The body stays energized and when some unfortunate person lays one hand on the metal body and another on something that has a path back to the neutral, that person is going to get a shock. Mike Sokol explains it pretty well in his No Shock Zone RV Safety web site.

An important part of that fault circuit is the "bond" between the ground and the neutral. It's obvious that if hot touches ground no circuit breaker will trip unless ground connects back to neutral. For reasons that only an electrical engineer can love, the connection should exist in only one place. This becomes tricky in the context of an RV because the RV may be self-powered (from an inverter or generator) or it may be grid-powered through a shore power connection at a campground, home, etc.

When powered via the shore power line it's important to use a setup that provides ground separate from the neutral. Use a 4-wire cord for split phase (US style) 240 volt service or a 3-wire cord for basic 120 volt service. Keep the ground and the neutral isolated from one another in the RV. The ground-neutral bond is provided upstream in the electrical system, often at or near the place where the electric utility's meter separates their system from the customer's premises wiring system.

When powered by the inverter or generator the ground and the neutral must be connected together. Some generators and inverters handle this function automatically, but others do not. It's important to understand how ones own equipment behaves in this regard. Lack of a ground-neutral bond is dangerous; extra ground-neutral bonding usually would cause only annoyances but could possibly cause more serious issues as well.
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Old 09-07-2017, 03:45 PM   #18
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No Shock Zone has been a great resource for me in trying to understand all this.

It sounds like it makes a lot of sense to seek out inverters and generators that have the bond built in to keep your system relatively simple.
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Old 09-07-2017, 03:50 PM   #19
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Well.. maybe. So long as there's a way of disabling the built-in bond during times when the RV is shore powered. As an example: if the RV is built with only a shore power cord, and that cord might be plugged in to a real shore power socket or into a generator, then having a ground-neutral bond in that generator makes it easy. The RV's system can always expect the ground-neutral bond to be provided externally.

However, if the same generator is to be hard-wired into the RV in some way, then its built-in bond could be problematic. There would have to be some means of interrupting it when plugged in to shore power. That's why I suggest that choosing an inverter or generator with a built-in bond doesn't remove the need for the RV builder to be aware of bonding issues.
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Old 09-07-2017, 03:53 PM   #20
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Quote:
Originally Posted by family wagon View Post
The suggestion to keep the metal body of an RV disconnected from the electrical system ground is unsafe for the reason described earlier: if (when) a fault happens such that a hot wire energizes the body, there needs to exist an intentional circuit or path so that a safety device will trip. If the metal body is left floating then that circuit doesn't exist. The body stays energized and when some unfortunate person lays one hand on the metal body and another on something that has a path back to the neutral, that person is going to get a shock. Mike Sokol explains it pretty well in his No Shock Zone RV Safety web site.

An important part of that fault circuit is the "bond" between the ground and the neutral. It's obvious that if hot touches ground no circuit breaker will trip unless ground connects back to neutral. For reasons that only an electrical engineer can love, the connection should exist in only one place. This becomes tricky in the context of an RV because the RV may be self-powered (from an inverter or generator) or it may be grid-powered through a shore power connection at a campground, home, etc.

When powered via the shore power line it's important to use a setup that provides ground separate from the neutral. Use a 4-wire cord for split phase (US style) 240 volt service or a 3-wire cord for basic 120 volt service. Keep the ground and the neutral isolated from one another in the RV. The ground-neutral bond is provided upstream in the electrical system, often at or near the place where the electric utility's meter separates their system from the customer's premises wiring system.

When powered by the inverter or generator the ground and the neutral must be connected together. Some generators and inverters handle this function automatically, but others do not. It's important to understand how ones own equipment behaves in this regard. Lack of a ground-neutral bond is dangerous; extra ground-neutral bonding usually would cause only annoyances but could possibly cause more serious issues as well.
You are gifted with the rare combination of quality knowledge and patience.

Thank you for your contributions. Good advice regarding electrical is a valuable commodity here.
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