Grounding necessary? question for extension cord style electrical system

[jazty]

Originally Posted by kazetsukai

An argument from authority is not an argument. If you're not willing to do the mental exercise of attempting to reach the truth, I'm not interested in your reply. I'm not willing to delegate my decisions to others blindly, I want to understand the logic.

You can do anything you want.. Just don't do it and plug into anyone else's world. You can create a risk for more than just yourself by doing things improperly (and yes, there is a proper and improper way to deal with AC electrical systems).

Originally Posted by kazetsukai

In a house, yes. I just gave you a scenario where the conditions are dynamic- buses that are mobile with inverters. They are not always going to be grounded or even connected to a pedestal, period. In those cases, what is the behavior of a system that grounds to chassis versus does not?

That is absolutely not a dynamic case. It will be statically wired with an on-off state. You'll just move it around more having it on wheels. Scenario: ungrounded power source with an extension plugged in. Extension cord exits the bus, frays and is in contact with the bus skin. What happens?
Even inside you could have a small, broken appliance that contacts some metal somewhere in the bus. That's hot skin for ya.


GFCIs were brought up above. I wouldn't be without them. My inverter does not have one built in so the first connection is to a GFCI, then the power distributes from there.

[kazetsukai]

Originally Posted by jazty

It will be statically wired.

By virtue of optionally being plugged into shore power, it is not static.

Originally Posted by jazty

Scenario: ungrounded power source with an extension plugged in. Extension cord exits the bus, frays and is in contact with the bus skin. What happens?

Its energized. In your setup, since the chassis is grounded, the GFCI trips.

I think its also worth asking what else you'd have to touch to create a circuit.

Scenario: You have a battery and an inverter. You've grounded the inverter to the chassis, you have the same appliances running as in your scenario, but there is no frayed wire or contact. You walk outside, you touch the skin and steel pipe running into the ground. Are you at risk of shock?

[jazty]

Originally Posted by kazetsukai

Scenario: You have a battery and an inverter. You've grounded the inverter to the chassis, you have the same appliances running as in your scenario, but there is no frayed wire or contact. You walk outside, you touch the skin and steel pipe running into the ground. Are you at risk of shock?

Of course you get no shock.. Everything is working as expected. Electrical hazards present themselves when things go wrong, which is real-life. That's what ground protection is for.. You don't give a hoot about it when everything is working properly. You become very thankful for it when things go awry.

[Mgulley82]

So are we saying busses and RVs aren’t safe unless you have a ground rod in the earth?

[kazetsukai]

Originally Posted by jazty

Of course you get no shock.

Can you perhaps tell me why a house ground leads to a copper-clad rod going into the earth instead of a large brick of metal?

Off-grid electrical systems that are non-mobile also ground using the same method- a copper rod in the ground. It seems that this is done for a reason, no?

I'm not trying to fight with you on this issue. My concern is only going as far as the chassis. If you only need to go that far, why would you run the ground from the pedestal into the bus at all? Why not just lead the hot and neutrals into the bus through a GFI, and then ground that GFI and all the outlets to the chassis? If its not okay to do that, why is it OK if the inverter "only" grounds to the chassis?

I'm evaluating risk, doing the mental labor of exploring possibility. I don't need a lecture.

[jazty]

Originally Posted by Mgulley82

So are we saying busses and RVs aren’t safe unless you have a ground rod in the earth?

No, we're discussing the grounding of the skin. You don't need a ground rod for the bus itself.


If you're using an inverter or generator it will most likely (hopefully) have the ground-neutral bond within itself. If it's properly listed (not all of them are. use GFCIs) a fault can be determined by current being returned through ground. A rod isn't needed for this function.


I think there's some confusion about neutral and ground. Ground should have zero current and will likely be bonded to neutral at a distribution box or the like, depending on the circumstances. Neutral should be return and is almost always rod grounded somewhere in a grid connected system.

[kazetsukai]

Originally Posted by jazty

If you're using an inverter or generator it will most likely (hopefully) have the ground-neutral bond within itself.

I think there's a UL standard around this about a relay connecting these when there's a load (or when the inverter is powered?), but not otherwise.

Edit:
UL1741 listed inverters must allow for the neutral-to-ground bond to only occur at the main AC service panel.
UL458-listed inverters have internal neutral-to-ground switching relays to allow for this bond to occur at the inverter if in off-grid mode, OR at the utility power service if it is connected to a utility hookup.

[jazty]

Originally Posted by kazetsukai

Can you perhaps tell me why a house ground leads to a copper-clad rod going into the earth instead of a large brick of metal?

Off-grid electrical systems that are non-mobile also ground using the same method- a copper rod in the ground. It seems that this is done for a reason, no?

I'm not trying to fight with you on this issue. My concern is only going as far as the chassis. If you only need to go that far, why would you run the ground from the pedestal into the bus at all? Why not just lead the hot and neutrals into the bus through a GFI, and then ground that GFI and all the outlets to the chassis? If its not okay to do that, why is it OK if the inverter "only" grounds to the chassis?

I'm evaluating risk, doing the mental labor of exploring possibility. I don't need a lecture.

All this ^
Research ground-neutral bond. I think I now understand where the confusion lies.


Ground-to-earth is not necessary. Ground in an AC circuit is a safety precaution. Current over the ground wire triggers disconnect devices.


Hot and neutral will have current when a device is working properly. Ground will have zero current. If there is any sizeable current on ground it is an indication that something has gone horribly wrong. Devices are built to monitor and shut this situation down. Ground doesn't actually mean "stuck in the ground".

[kazetsukai]

Originally Posted by jazty

Ground-to-earth is not necessary. Ground in an AC circuit is a safety precaution. Current over the ground wire triggers disconnect devices.


Hot and neutral will have current when a device is working properly. Ground will have zero current. If there is any sizeable current on ground it is an indication that something has gone horribly wrong. Devices are built to monitor and shut this situation down. Ground doesn't actually mean "stuck in the ground".

This is a good explanation, and in this case I do agree with your overall argument about grounding to chassis.

[jazty]

Originally Posted by kazetsukai

I think there's a UL standard around this about a relay connecting these when there's a load (or when the inverter is powered?), but not otherwise.

Edit:
UL1741 listed inverters must allow for the neutral-to-ground bond to only occur at the main AC service panel.
UL458-listed inverters have internal neutral-to-ground switching relays to allow for this bond to occur at the inverter if in off-grid mode, OR at the utility power service if it is connected to a utility hookup.

You do only want one neutral-to-ground bond. None of the inverters I own have a relay, but they are fully disconnected from the AC wiring circuit when grid power is provided.. otherwise smoke..


The better UL listed inverters will allow for grid-tied connection without disconnecting them entirely. The better ones even double as battery chargers.

[roach711]

Jatzy is correct.

1) Ground your AC panel to the skin. If there is no ground connection a loose hot wire touching the skin would not trip your breaker and the skin would become energized. On a wet day someone with feet on the ground and hand on a metal door frame will get a shock, maybe a fatal one.

2) Ground and neutral wires should not be connected at your bus power panel. Use a branch panel with separate bonding bars. Ground and neutral should only be connected at the shore power panel.


In the picture of your breaker box, the wires with the black tubing would normally be considered to be "coded black" and would be expected by an electrician to be a hot wire (black = hot, white = neutral, green = ground). I expect that they were marked that way to differentiate between circuits.



The white neutral wires should be attached to the bonding bar in the upper left, not on the ground bar with the green wires.

[PNW_Steve]

Originally Posted by roach711

Jatzy is correct.



1) Ground your AC panel to the skin. If there is no ground connection a loose hot wire touching the skin would not trip your breaker and the skin would become energized. On a wet day someone with feet on the ground and hand on a metal door frame will get a shock, maybe a fatal one.



2) Ground and neutral wires should not be connected at your bus power panel. Use a branch panel with separate bonding bars. Ground and neutral should only be connected at the shore power panel.

Well said.

In addition to the above, if you have a generator, ground and neutral should be bonded at the generator.

[o1marc]

I can't find it now, but there was a video posted previously showing the proper grounding methods and how not to electrify the shell.

[Rivetboy]

My 2 cents is to reland those grounds seperately into an individidual ground screw and do not nick the wires when you strip them. With the vibration in your bus they are prone to breaking at the introduced flaw. Also , no squirted strands.
A pair of Ideal or Klein strippers is a wise investment.

[kazetsukai]

Originally Posted by roach711

Jatzy is correct.

To clarify: Assuming there are GFCIs at the right places. Jatzy's explanation was enlightening in this regard. A floating ground without GFIs have all the dangers I pushed back on earlier.

I guess my next line of questioning would be dealing with any electrostatic potential differences between the chassis and earth (bonding pedestal ground to chassis ground should be sufficient when hooked up), as well as all the noise from having:

• Bus DC Negative
• Solar Panel Ground
• Inverter AC Ground
• Neutral bond

All connected to the same ground.

[roach711]

Originally Posted by kazetsukai

I guess my next line of questioning would be dealing with any electrostatic potential differences between the chassis and earth (bonding pedestal ground to chassis ground should be sufficient when hooked up), as well as all the noise from having:

• Bus DC Negative
• Solar Panel Ground
• Inverter AC Ground
• Neutral bond

All connected to the same ground.

Kaz - I believe the Heisenberg Principle covers all that. We should also investigate the effect of dark matter on solar charging. There might even be some federal grants available for that.

[w8one]

Roach711 has it right.

In a AC circuit:
The purpose of ground is to have a 0 Volt reference, by grounding all metal cases. If short circuit occurs, where humans or other animals can touch something conductive the fuse or breaker should trip BEFORE the human or animal gets shocked.
In ALL cases the neutral and grounds should be isolated from each other, no matter if it is an appliance, house, rv, or boat.
Bonding (Connecting ground to neutral) occurs at the source of AC power only.
For houses this at the main service panel. Having multiple paths to ground or NO paths to ground is what causes electrocution ie. shocks. Your breaker or fuse box in your rv is NOT a power source. Power from the pedestal, inverter, and generator all are sources BUT you can only have ONE bond at a time. A transfer switch will let you select which one you want to use.
There are special "brown out inverters" that can combine two sources safely.
In a DC circuit:
Grounding the vehicle is a shortcut by manufactures (to save money) by NOT running 2 wires to every device than needs power. Because you wont get killed by 12 Volts DC. This has the benefit of reducing or eliminating "rf noise" from your stereo, and saves them thousands of dollars.
All 12v DC sources should be tied together if you want them to work together.
Its fine for AC and DC systems to use the ground.

[Drew Bru]

Originally Posted by w8one

Roach711 has it right.

In a AC circuit:
The purpose of ground is to have a 0 Volt reference, by grounding all metal cases. If short circuit occurs, where humans or other animals can touch something conductive the fuse or breaker should trip BEFORE the human or animal gets shocked.
In ALL cases the neutral and grounds should be isolated from each other, no matter if it is an appliance, house, rv, or boat.
Bonding (Connecting ground to neutral) occurs at the source of AC power only.
For houses this at the main service panel. Having multiple paths to ground or NO paths to ground is what causes electrocution ie. shocks. Your breaker or fuse box in your rv is NOT a power source. Power from the pedestal, inverter, and generator all are sources BUT you can only have ONE bond at a time. A transfer switch will let you select which one you want to use.
There are special "brown out inverters" that can combine two sources safely.
In a DC circuit:
Grounding the vehicle is a shortcut by manufactures (to save money) by NOT running 2 wires to every device than needs power. Because you wont get killed by 12 Volts DC. This has the benefit of reducing or eliminating "rf noise" from your stereo, and saves them thousands of dollars.
All 12v DC sources should be tied together if you want them to work together.
Its fine for AC and DC systems to use the ground.

This is an excellent post. Explains everything in layman's terms and is just the thing for a dummy like me! I really appreciate it.

[roach711]

"Grounding" can be confusing when mixing AC and DC in the same vehicle. As W8one said, the third green ground wire in an AC system is a safety feature. On the other hand, a DC ground is the same as the AC white neutral wire, that being a return wire or path that completes the circuit. Most steel vehicles use the body and frame as the return path back to the battery (doesn't work in a fiberglass body bus like mine) so a typical vehicle DC circuit is one hot wire running to the load (light, radio or whatever) and a short wire attached to the steel body.



So basically, when we're discussing grounding in a vehicle DC system we're talking about making a good circuit.


When we talk about grounding in an AC system we're talking about a safety feature that protects wiring and people.



Nobody said it had to make sense.

[Rivetboy]

Originally Posted by w8one

Roach711 has it right. Its fine for AC and DC systems to use the ground.

And star washers on a ground that's shiny in a high vibration enviornment coated with your favorite whatever is the best defense against that old arch enemy, difference of potential in grounds.
Insert evil BUUUhaha here..