Grounding theory question

[jetjaguar]

Hi Team,
I hesitate to ask these questions because I'm not sure even *how* to ask what I'm trying to ask. Sorry in advance. I just don't have a good intuitive feel for grounding and I need to talk it out in some way.

What I think I know: Grounding a system provides an alternate path for electricity to flow so instead of electricity flowing into a human, it flows into the literal earth in an earth grounded system or into the chassis of a vehicle in the case of a mobile system.

Question: In the case of grounding to a chassis, where does the electricity go once it hits the chassis? Does the chassis heat up? Does the current spike and an equipment breaker trip or something? Does/should a fuse blow? Everything I read just says the electricity goes to the chassis. I want to know what happens after that.

In my house, I get that when I ground a washing machine, for example, if a short occurs, the flow will go through the frame of the washer and back to the panel where a breaker will trip due to high current, thus disconnecting the circuit. Please correct me.

Practical application: Let's say I have a battery bank powering a 1000W inverter. The inverter has a small ground lug to which a grounding wire can be attached. Then let's say I connect an AC Appliance to the inverter. Can I ground the inverter to the frame of my washing machine and establish a ground in this way?

 

[acdoctor]

If there is no pathway to earth the chassis becomes energized. If you become the path from chassis to earth you will have a problem.
I have seen mobile homes on blocks in the summer become energized. The door knob would get you. The owner told me you can’t use the back door because of the cement steps. The front had wood.

 

[jetjaguar]

If there is no pathway to earth the chassis becomes energized. If you become the path from chassis to earth you will have a problem.
I have seen mobile homes on blocks in the summer become energized. The door knob would get you. The owner told me you can’t use the back door because of the cement steps. The front had wood.

Hah! Okay, this comports with some research I have done. I was reading about lightning strikes as a proxy for this problem. The internet told me that the lightning would pass through the wheels and tires and into the earth. So it seems to me I could just ground my described system to my washing machine since it's connected to house ground. Right?

 

[acdoctor]

Lightning is whole different animal than a ground fault. Lightning can go to ground through jacks easily. Steel belt tires are doable as well. But the easier path the better. The quicker you can dissipate lightning in earth the less damaging. Telecom grounds everything fencing, metal on building, rebar, battery racks all in a specific order to dissipate it before getting to the equipment.

 

[jetjaguar]

Yeah, I get that it's a different level of the game, but I am reading everything I can to get my head around grounding.

 

[Zil]

The only time a vehicle needs an earth ground is when it is plugged into the power grid. That ground can only be through the green wire in the pedestal back to the main service panel. "Hot Skin" in a vehicle is because the chassis is not properly tied back to the service panel.
The inverter will have a case lug that should be connected to the chassis. The chassis should be connected to the DC negative BusBar.

As posted above, lightning is a different beast. There is nothing to protect from a direct lightning strike. There are means to prevent most direct lightning strikes. But not in a mobile vehicle.

 

[WYtreasure]

Yeah, I get that it's a different level of the game, but I am reading everything I can to get my head around grounding.

You are going to make yourself dizzy trying to figure this out, I did.
Better hurry though, thunderstorms are blowing by me and headed for you.

DC Ground Rod/Grounding Electrode

My inverter is connected to the ground bus bar/grounding conductor in both the AC Main panel as well as the AC sub-panel to which it is connected. There is a lug on the inverter casing specifically for "DC Ground." The manual shows this ground being connected to the battery enclosure - and...

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[jetjaguar]

The only time a vehicle needs an earth ground is when it is plugged into the power grid. That ground can only be through the green wire in the pedestal back to the main service panel. "Hot Skin" in a vehicle is because the chassis is not properly tied back to the service panel.
The inverter will have a case lug that should be connected to the chassis. The chassis should be connected to the DC negative BusBar.

In a vehicle, the ground is the chassis (when not on grid), which, in the event of a short, passes current to the chassis, which will turn pass it to mother earth. Is this correct?

 

[WYtreasure]

I dunno. Rubber tires prevent current from passing.

 

[jetjaguar]

I dunno. Rubber tires prevent current from passing.

This is sort of the heart of my question. Let's say a short occurs and current is now hitting the chassis. Now what happens? Does the chassis heat up? Does the short get detected by equipment and then the circuit opens?

Conflicting information on the internet about whether the tires actually do insulate.

 

[AntronX]

In a vehicle, the ground is the chassis (when not on grid), which, in the event of a short, passes current to the chassis, which will turn pass it to mother earth. Is this correct?

Not to mother earth but to the inverter neutral wire which would complete the short circuit current path and trip the breaker or the inverter (with the assumption that ground and neutral are bonded somewhere).

 

[jetjaguar]

thanks @AntronX . In a DC system are neutral and 'negative' synonymous?

 

[AntronX]

In a DC system are neutral and 'negative' synonymous?

No, i don't think so. There is no DC polarity with AC wiring. Neutral should have 0 volts in relation to safety ground. Hot or Line has whatever is the AC system voltage in relation to safety ground.

 

[WYtreasure]

If the breaker does not trip, the vehicle may experience what is called "a fire of known origin".

You will have a self-contained short. Mother earth won't rescue you. I don't see any point in discussing tires being conductive.

Positive and Negative are terms commonly used with DC.
Line, Neutral and Ground are terms commonly used with AC.
Sometimes folks mix them up, me included.

I think these are excellent references:

Commonly used Forum Acronyms & Abbreviations

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Impress your friends by using correct units and abbreviations

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[jetjaguar]

If the breaker does not trip, the vehicle may experience what is called "a fire of known origin".

You will have a self-contained short. Mother earth won't rescue you. I don't see any point in discussing tires being conductive.

Positive and Negative are terms commonly used with DC.
Line, Neutral and Ground are terms commonly used with AC.
Sometimes folks mix them up, me included.

LOL @ "fire of unknown origin". This thread is helpful. Thank you.

 

[Zil]

This is sort of the heart of my question. Let's say a short occurs and current is now hitting the chassis. Now what happens? Does the chassis heat up? Does the short get detected by equipment and then the circuit opens?

Conflicting information on the internet about whether the tires actually do insulate.

The tires do insulate on such low voltage as found in dc battery and the campground outlet that the RV is plugged into. That is why it is necessary to have the grid earth ground wire, green?, properly connected to the chassis.
What short are you referencing? Why is the circuit not protected by a fuse?

 

[DerpsyDoodler]

Hi Team,
I hesitate to ask these questions because I'm not sure even *how* to ask what I'm trying to ask. Sorry in advance. I just don't have a good intuitive feel for grounding and I need to talk it out in some way.

What I think I know: Grounding a system provides an alternate path for electricity to flow so instead of electricity flowing into a human, it flows into the literal earth in an earth grounded system or into the chassis of a vehicle in the case of a mobile system.

Question: In the case of grounding to a chassis, where does the electricity go once it hits the chassis? Does the chassis heat up? Does the current spike and an equipment breaker trip or something? Does/should a fuse blow? Everything I read just says the electricity goes to the chassis. I want to know what happens after that.

In my house, I get that when I ground a washing machine, for example, if a short occurs, the flow will go through the frame of the washer and back to the panel where a breaker will trip due to high current, thus disconnecting the circuit. Please correct me.

Practical application: Let's say I have a battery bank powering a 1000W inverter. The inverter has a small ground lug to which a grounding wire can be attached. Then let's say I connect an AC Appliance to the inverter. Can I ground the inverter to the frame of my washing machine and establish a ground in this way?

The purpose of a ground is to allow high current to flow so that in the event of a short, a breaker can trip. A ground conductor should be attached to something massive (literally, large mass) so that it can absorb and dissipate all that charge without becoming charged itself. Earth is the best "ground" we have for that purpose. Chassis are the substitute in the mobile space because they are the most massive thing
you can connect to on the vehicle. Just remember that the purpose in either case is to make a breaker trip. If no breaker trips, the chassis will become energized and bad things can happen. Read the link in my signature about grounding.

 

[jetjaguar]

The tires do insulate on such low voltage as found in dc battery and the campground outlet that the RV is plugged into. That is why it is necessary to have the grid earth ground wire, green?, properly connected to the chassis.
What short are you referencing? Why is the circuit not protected by a fuse?

I see now about the neutral and ground being bonded to neutral in many discussions, and this is part of what I was missing. In this case, yes, a breaker/fuse should break the circuit. Thank you!

 

[jetjaguar]

The purpose of a ground is to allow high current to flow so that in the event of a short, a breaker can trip. A ground conductor should be attached to something massive (literally, large mass) so that it can absorb and dissipate all that charge without becoming charged itself. Earth is the best "ground" we have for that purpose. Chassis are the substitute in the mobile space because they are the most massive thing
you can connect to on the vehicle. Just remember that the purpose in either case is to make a breaker trip. If no breaker trips, the chassis will become energized and bad things can happen. Read the link in my signature about grounding.

This is a very helpful description, especially the "large mass" part. I suspected this might be the mechanism, but I didn't have a good intuitive sense of things. Also I didn't see any link in your sig about grounding, maybe it was truncated?