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Old 11-01-2018, 05:18 PM   #1
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120 volt AC breaker box: ground to chassis or not?

I'm sure this is beating a dead horse but I am getting conflicting information from different sources.

Do I need to ground my 120 volt AC to the bus?

As of now, all my breakers run to a single grounding busbar inside the work center. This includes both breakers on either side of my inverter and my breaker for my rooftop a/c which is on a completely separate input system. I have gone as far as running a ground wire from each metal breaker box to the grounding busbar on the breaker box.

My question is: Do I need to run a ground wire from this busbar to my chassis/frame?

If my understanding is correct, grounding all of these will prevent "hot skin" if there is a break/loose HOT wire that comes in contact with the bus. I then read it's the opposite? Help me skoolie-wan, your my only hope!

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Old 11-01-2018, 05:20 PM   #2
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Extra info:

I have kept all neutral wires on a separate busbar from the grounds. My inverter has automatic transfer switch.
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Old 11-01-2018, 06:17 PM   #3
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Get an experienced pro to help with shore power stuff.
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Old 11-01-2018, 06:38 PM   #4
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Well, the electrician's I talked to didn't know. From reading a different thread it's not ground the box to the bus but grounding the bus to box. I'll run my ground a ground to the chassis/frame.
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Old 11-01-2018, 06:52 PM   #5
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The info you're looking for should be in here somewhere- http://http://noshockzone.org/rv-ele...0%93-hot-skin/
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Old 11-01-2018, 07:24 PM   #6
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Hello, My name is Kevin, I'm currently in my 5th and final year of my union inside wireman apprenticeship. Sitting here in class, working through a code lesson and had to look it up.

Found this info in my 2017 NEC book. 551.56 Requires bonding of all exposed non-current carrying parts that are likely to become energized shall(must) be effectively bonded to the grounding terinal or enclosure of the panelboard There is an exception to NEC code 551.56.

Any recreational vehicle that employs a unitized metal chassis-frame construction to which the panelboard is securely fastened with a bolt(s) and nut(s) or by welding or riveting shall be considered to be bonded.



If your panel is not bonded by any these means, you shall(must) run a bonding wire from the chassis to the grounding terminal in your panel.

The bonding conductor shall be solid or stranded, insulated or bare, and shall be 8 AWG copper minimum.
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Old 11-01-2018, 07:30 PM   #7
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Quote:
Originally Posted by EastCoastCB View Post
The info you're looking for should be in here somewhere- http://http://noshockzone.org/rv-ele...0%93-hot-skin/
Good info!

It is correct to ground your 120V panel to the chassis of the bus.

Also, make sure that the neutral bus in your breaker panel is NOT bonded to ground. Many breaker panels (load centers) come out of the box with a bonding strap between neutral and ground. This should be removed.


However..... When you connect to generator power you will will need to bond ground & neutral.

Ground and neutral should only be bonded at the source. IE: generator or shore power connection.
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Old 11-01-2018, 08:45 PM   #8
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This seems right but have to wonder 120ac grounded to the bus, and 12 volt dc grounded to the bus, just seems this would do something not good. On my bus both are grounded, so clearly it works.

Anyone have an explanation as to why this does not create a problem being ac/dc plus different voltage?
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Old 11-01-2018, 09:29 PM   #9
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Thank you for the help all.

Just reread the hotskin article ECCB,.great info. I should buy that book.

PNW-Steve, thanks. I made sure to keep ground far from neutral in the main panel.

Helio- great info. I'll step up.my wire size for.the ground connection. I have some spare 8 ga laying around from the old bus electric.

Now, I just need to.call champion and find out about my Genny and if they bonded ground to neutral or not. My inverter has the auto transfer switch but my rooftop doesn't run off the main panel or the inverter and j want to make sure that's plugged in correctly as well.

Thanks again!
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Old 11-01-2018, 09:42 PM   #10
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Quote:
Originally Posted by Ronnie View Post
This seems right but have to wonder 120ac grounded to the bus, and 12 volt dc grounded to the bus, just seems this would do something not good. On my bus both are grounded, so clearly it works.

Anyone have an explanation as to why this does not create a problem being ac/dc plus different voltage?

The confusion arises because the term "ground" doesn't mean the same thing in AC and DC circuits.



A DC ground completes the circuit, just like an AC neutral wire. The AC ground wire is a safety feature that only carries current momentarily when there is a fault in the system like a loose hot wire touching metal. Without the ground connection between the bus body and AC breaker box there would be no way for the breaker to sense a hot wire touching the bus body. That would mean the breaker would not trip and the bus body would be energized. A shocking situation!
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Old 11-02-2018, 07:22 AM   #11
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Right, you are grounding the ground bar, not the neutral. Separate the neutral from the ground.
Quote:
Originally Posted by roach711 View Post
The confusion arises because the term "ground" doesn't mean the same thing in AC and DC circuits.



A DC ground completes the circuit, just like an AC neutral wire. The AC ground wire is a safety feature that only carries current momentarily when there is a fault in the system like a loose hot wire touching metal. Without the ground connection between the bus body and AC breaker box there would be no way for the breaker to sense a hot wire touching the bus body. That would mean the breaker would not trip and the bus body would be energized. A shocking situation!
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Old 11-07-2018, 06:56 PM   #12
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If you have a screw holding an electrical box to the bus frame, it is partially grounded via proper bonding within the electrical box. Might as well use #6 ground wire and bond the panel to the chassis. By doing this there is the path of least resistance for AC current to trip whichever breaker is protecting the circuit; either the panel in the bus or the shore panel.

A ground strap would be a wise investment to attach to the underbelly of your bus. In the event you get a “hot” chassis this strap could save an occupant from getting jolted from AC or DC power.
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Old 11-07-2018, 11:34 PM   #13
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My 12 volt system was already grounded with 4/0 wire. I have grounded the bus to the 120 busbar with 8 gauge as well. Thanks for all of the reply’s and information
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Old 11-09-2018, 04:42 PM   #14
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Yes, you need to have your "safety" conductor bonded together. So,like a lot of people say in north american 120 volt wiring, common practice is:

black is "hot" or where the electrons come from
white is "neutral" or where the electrons want to go to
green is "earth" or safety, which is a catch-all for failures

You always "bond" or connect electrically your safety catch-all to the case or surrounding to everything else that is conductive but electrically zero. Various situations call for your earth to be connected, "bonded" to neutral, or isolated, like others have said.

What piqued my interest is nobody addressed your concern about grounding "bonding" both the AC and DC systems together. Which, by the way, is totally fine in your case.

I'll just go through some thoughts, feel free to skip the blather if you already know about this stuff.





120 volt single phase AC power is defined by the voltage potential swinging through zero volts 60 times per second. Peak to peak, "120 volt AC" is actually much higher voltage, approximately 170 volts. The Root Mean Square of the sinusoidal curve as voltage swings back and forth balances out to 120 volts potential.

DC power in vehicles is a constant voltage potential one direction.

Electrical power from batteries is a chemical reaction, specifically a type of oxidization and reduction of different types of metals sandwiched between a conductive medium (the electrolyte). You have to physically stack up your pile of materials to get the electrons to flow.

This means your stack sort of sits there chemically draws electrons from the material until they reach equilibrium (also known as the battery going dead)

This inherently means that battery sources are DC - Direct current.

AC power, like previously described, is mostly derived from rotational generation. Like a big spinning thing. We can go back in time to the industrial revolution and steam power to see the origins of AC, if needed.

Alternating current ALSO originates, technically, from anode and discharges to cathode. However, they are not referred to as such, because they are switching roles periodically (like, 60 times a second). Therefore we can just refer to them as "electrodes" aka "the place that electrons come from"

In all cases, DC power and AC power can be derived from physical movement, through a magnetic mass (like iron) and inducted into a conductor (like copper) which pushes electrons out the end of the conductor.

Folks realized there were a lot of benefits to Alternating Current vs Direct Current. From safety all the way to the amount of voltage that can safely be distributed via AC.

We won't get into many details about that, but one of the prime safety benefits of AC is that it is self-extinguishing in the case of a fault. A DC arc will continue to persist as long as power exists. An AC arc self-extinguishes 60 times a second, due to it's voltage potential crossing zero 60 times a second.

Basically, you get a big BANG with DC and an big BUZZ with AC.

Work with electricity only happens when you have a potential between your anode and cathode, or between your electrodes. It doesn't matter if it's cycling 60 times per second or constant.

Therefore, when you are "creating" AC power from an inverter or a generator, there is always a "base" or reference voltage of which the relative potential from it to everything around it should be zero volts.

The battery anode, (the negative post) reference is zero. The energy converted to alternating current uses the same zero reference. Generators that may be attached to the same system use the zero reference in the electrical coils.

This is the reason that your inverter or generator generally maintains the only "bond" between your earth and neutral. The alternating current electrons being shuffled back and forth through those devices use the "earth" as the reference for "ground". Without that reference, you get a potential difference, and therefore the possibility of electrons flowing between earth and neutral, and therefore shock hazards.

When power originates from somewhere else (like grid power) the earth to neutral reference is maintained in the utility itself. Adding secondary bonds between earth and ground in those systems can actually add a potential hazard (shock hazard) when an inequality exists, such as consuming some of that energy in a motor, light, or other device.


If you've read this far, the summary is this: internally originated AC electrical sources are friends with internally originated DC electrical sources, because they generally share the same reference voltage. There are of course many exceptions for this, but in this case they are completely compatible and actually necessary.
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