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Question on grounding


4x4ff

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I don't have a problem just a question that popped into my head the other day. Just got done installing my new inverter to run the fridge while traveling. I was hooking up the chassis ground from the inverter to the chassis. Whenever I set my front jacks and the rear stabilizers I have some big 6 x 6 blocks that I always set them on. So basically the entire unit is isolated from the ground. Should the unit be in contact with the ground in order to 'ground' it in case of an electrical problem or will in not make a difference? I'm not talking about the 12v system I mean the 110v system. Seems to me if the unit was in contact with the ground it could dissipate an electrical short better but then I see everyone using plastic ground pads under all their jacks so not sure if my theory is valid.

 

No biggie...just a random thought that I am sure somebody can explain.

 

Steve

2007 Pilgrim M378 SA4S-5

 

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If plugged into shore power, your frame is grounded via the power cord.

 

If not on shore power and you power source is a generator or inverter, the power source is tied to the frame, i.e. the loop from power source to ground is within the RV.

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If plugged into shore power, your frame is grounded via the power cord.

 

If not on shore power and you power source is a generator or inverter, the power source is tied to the frame, i.e. the loop from power source to ground is within the RV.

Exactly! :)

Good travelin !...............Kirk

Full-time 11+ years...... Now seasonal travelers.
Kirk & Pam's Great RV Adventure

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Good questions 4 x 4

 

(A) FIRST HERES A BIT OF THEORY (Engineer/Attorneys are just "wired" that way lol)

 

You may be confusing or mixing/matching EARTH GROUNDING with Neutral/Ground BONDING and/or the purpose and function of the Equipment Grounding Buss and Conductor. Obviously, the RV's Chassis/Frame (other then tires etc) is NOT attached to earth ground. However, the Chassis/Frame ISSSSSSSSSS connected to the incoming Utility "EQUIPMENT GROUNDING CONDUCTOR" so if there's a hot to chassis short there's a low impedance fault current return path back to the panel so the breaker trips and clears the fault.

 

NOTE if there wasn't any Chassis/Frame to Equipment Grounding Conductor bond, but instead ONLY the RV wired to an earth ground rod and a hot shorted to frame MOTHER EARTH IS PROBABLY TOO HIGH RESISTANCE CONDUCTOR so the breaker wont trip and if you touch the RV you will still get shocked !!!!! See why having the RV bonded to the Utility Equipment Ground Conductor is more effective then ONLY driving a ground rod and attaching it to the RV in cases involving utility power???

 

The Utility Secondary Power at the Service Entrance has at one place (Single Point Grounding) its Neutral connected to a "Grounding Electrode" often consisting of "made electrodes" such as driven into mother earth copper rods IE The Neutral is "Earth Grounded" to protect against lightning and surges PLUS in the RV Parks distribution system (NOT the RV Panel), the Neutral Buss is BONDED to the Equipment Ground Buss.

 

When you use an onboard built in Genset or an Inverter, they are configured as a "Separately Derived Source" and their Neutral is bonded to a "Grounding Electrode" but in this case instead of that being a rod driven into earth, its the RV Chassis/Frame similar to how in steel high rise structures the iron is a "Grounding Electrode" ALSO Ground is BONDED to Neutral (Genset or Inverter) so the system acts just like when you're connected to the Utility

 

NOTE some small portable gensets have a Floating Neutral in which case there IS NO NEUTRAL GROUND BOND but generally the built in onboard gensets have the Neutral Ground BOND along with the Neutral to "Grounding Electrode" (Chassis/Frame). An Inverter operates in a similar fashion to a Genset in which case when its in use there's a Neutral Ground BOND plus attachment to a "Grounding Electrode" (RV Chassis/Frame) which may take place via a Relay to avoid having more then one single Neutral Ground bond.

 

( B) NOW TO YOR QUESTIONS/STATEMENTS

 

"So basically the entire unit is isolated from the ground."

 

Its maybe called "isolated" direct from mother earth where it sets (subject to tires) HOWEVER, its frame is bonded to the Utility Equipment Grounding Conductor,,,, which is bonded to the Utility Neutral,,,,,,,,,, which is attached to mother earth SO ITS NOTTTTTTTTTTTTTT really isolated from ground.

 

 

" Should the unit be in contact with the ground in order to 'ground' it in case of an electrical problem or will in not make a difference?"

 

It wont hurt if its in contact with earth WELL DUH but if there's a hot to RV short its the Equipment Grounding Conductor that can carry sufficient fault current back to the panel so the breaker trips and clears the fault UNLIKE ONLY the jacks to earth which may well NOT trip the breaker and you get shocked.

 

"Seems to me if the unit was in contact with the ground it could dissipate an electrical short better"

 

That statement does have some validity. If there was electrostatic or surge/lightning induced voltage present on the RV frame causing it to rise above mother earth potential and the RV was attached to mother earth SURE that can bleed off the charge,,,, but absent a bond to the Utility Equipment Ground Conductor subject to earths moisture and mineral content and distance to panel, metal jack pads to earth alone probably wont cause the breaker to trip and clear the fault and you still get shocked !!!!!!!!!!!!!

 

Sorry, but that's a brief as I can make it lol Its impossible to explain in a paragraph what may take books and study and experience to fully comprehend (some engineers and techs and electricians still don't get it) but hey I do the best I can

 

DISCLAIMER its been yearsssssssss since I retired from Electrical Engineering so this may be wrong as rain, in which case an expert can correct me (please do, Im never too old to learn) but I believe its still correct DO WHAT THE NEC SAYS NOT ME OR ANYONE HERE is my final advice.

 

DISCLAIMER 2 I don't have any Inverter schematics or diagrams whatsoever and not exactly sure how a relay or switch works to achieve a Neutral Ground Bond when powered up (just a simple relay from Neutral to Ground perhaps???) and/or Neutral to Chassis/Frame bond etc SO THE ABOVE MAY BE INCORRECT but its still correct in theory I believe???? Perhaps Jack M has such information and can correct me if necessary.

 

John T

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That is why transfer switches, including the one inside the Inverter, transfer the Neutral as well as the Hot leg/s to maintain the correct Neutral/Ground bonding.

 

The on board power sources, Inverter or generator, provide their Neutral/Ground bond, the off board source, shore power, at the power panel closest to the power plant.

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Joey - 2016 Bounder 33C Tige - 2006 40' Travel Supreme
Sparky III - 2021 Mustang Mach-e, off the the Road since 2019
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Mark and Dale, I see you have a good handle on this.

 

"That is why transfer switches, including the one inside the Inverter, transfer the Neutral as well as the Hot leg/s to maintain the correct Neutral/Ground bonding."

 

EXCELLENT to expand a bit for anyone who cares lol, in home back up generator systems that use Transfer Switches for 120/240 Volt Single Phase Three Wire Service, sometimes ONLY a cheaper Two Wire (two hots switched) Switch is used in which case the Genset is NOT configured as a Separate Derived Source,,,,,,,,,,Neutrals are NOT switched,,,,,,,,,,,,,,Genset uses a FLOATING Neutral (any internal Neutral Ground Bond is severed) ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,Gensets case/frame is connected to the utility Equipment Grounding Conductor same as any other non current carrying conductive enclosures. I prefer a three pole switch to switch Hots and Neutral and configure the Genset as a Separate Derived Source. At least that's my best recollection but again its been yearsssssssssssss since I designed and specified such so no warranty on this whatsoever.

 

"The on board power sources, Inverter or generator, provide their Neutral/Ground bond, the off board source, shore power, at the power panel closest to the power plant."

 

In our jurisdiction as far as the end users secondary service is considered, REMC and Public Service, the incoming Neutral was Earth Grounded (Earth served as the Grounding Electrode) at EITHER: The weatherhead riser where overhead utility connected to customer,,,,,,,,,,,,,,,,,,,,,,,,OR,,,,,,,,,,,,,,,,,,,,,,,,,In the Meter Base,,,,,,,,,,,,,,,,,,,,,,,,,OR,,,,,,,,,,,,,,,,,,,,,,,,, in the Main Distribution Panel. Then in the Main Distribution Panel often Neutral Ground Bonding was accomplished by the use of a Cross Tie Bar that bonded the Ground Buss to the Neutral Buss. On the HV Primary, Neutral was earth grounded at every 3 overhead utility poles. Of course, at service transformers Neutral bonded to the Grounding Electrode Conductor (No 4 bare copper wire down pole to ground rod) and the case of the transformer.

 

Fun sparky chatting with you at the risk of boring others to tears lol

 

John T

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(A) FIRST HERES A BIT OF THEORY (Engineer/Attorneys are just "wired" that way lol)

I do believe that both careers have classes that teach how to take a simple question and make the answer very complicated... :lol:

Good travelin !...............Kirk

Full-time 11+ years...... Now seasonal travelers.
Kirk & Pam's Great RV Adventure

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Good afternoon my friend, you state "I do believe that both careers have classes that teach how to take a simple question and make the answer very complicated..."

 

TRUE perhaps lol all are entitled to their own opinion. FYI Here's where I'm coming from. I try my best to educate the poster and EXPLAIN the Theory as well as the Practical Application to educate the poster as well as other readers, because if they understand the theory, they can figure things out the next time and be safe. For years older more experienced gentleman have helped me and I figure now its payback time, so I try to help others in the only way I know how. I subscribe to the old proverb "Give a man a fish, feed him a meal, teach him how to fish, feed him for life" Of course, I realize its impossible to teach in a paragraph on a Forum what can take years of study and experience to comprehend, but hey I try my level best. I've NEVER had anyone who asks a question (such as 4 x 4 here) complain I gave them too much information!!! What you consider "complicated" may not be complicated to one who has learned and now understands that which I have explained. While the theory of Grounding and Bonding and the differences and similarities may be "complicated" in your words, ITS NOT TO THOSE who understand it. I figure if 4 x 4 who asked the question doesn't like my answer, HE (or you or anyone else) is free to ignore it. However, its indeed a "complicated" subject and there's no way around that or sugar coat or simplify it, sorry. In my 40 year career in the electrical industry I read too many horror stores where Billy Bob and Bubba who thought they "knew it all" and it was "simple" ended up getting electrocuted or their house burned down grrrrrrrrrrrrrrrr. I try to remain polite, professional and courteous in my responses and never belittle a mans question or chosen occupation. I worked long and hard to get my education and where I'm at, and yes I'm very proud of it.

 

PS if you think my Grounding and Bonding explanation was "complicated" or long winded lol, look at this EXCELLENT PRESENTATION written by Jack Mayer who is a great educator on this forum https://docs.google.com/document/d/1X0A0bD4D-0n-GJmtEKK_ls5mYFdupgmqA1Xtb06JDLM/edit?pli=1

 

 

Take care my friend and thanks for all the help you have provided me and the other gents here. Perhaps I can visit you sometime in 2017 so us old retired sparkies can talk the talk lol ???

 

Best wishes and God Bless all here

 

John T

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John, I hate to say it, but I completely understood everything you said about grounding, but I used to have one of those "half amper" licenses (PLT) and at every single 8 hour continuing ed class there was a minimum of two hours spent on grounding. It is actually surprising the number of individuals that don't grasp the difference between grounding and grounded......

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Simplest answer I can think of:

 

If the RV's power source is totally isolated from ground, it doesn't matter if the RV is grounded or not. The voltage is not ground referenced, so there's no way it can deliver a shock to someone standing on the ground. Just like a bird can land on an energized power line and not get shocked.

 

BUT, if the power source has any connection to ground (i.e. utility power) then the RV must also be grounded to keep stray voltage from leaking to it's frame and skin. Since the voltage is ground referenced, it will flow through any path that comes between the RV and ground. If that path happens to be you when you touch the skin of the RV, you will get a shock.

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Simplest answer I can think of:

 

If the RV's power source is totally isolated from ground, it doesn't matter if the RV is grounded or not. The voltage is not ground referenced, so there's no way it can deliver a shock to someone standing on the ground. Just like a bird can land on an energized power line and not get shocked.

 

BUT, if the power source has any connection to ground (i.e. utility power) then the RV must also be grounded to keep stray voltage from leaking to it's frame and skin. Since the voltage is ground referenced, it will flow through any path that comes between the RV and ground. If that path happens to be you when you touch the skin of the RV, you will get a shock.

Very good answer! If the power supply is inside of the RV, no earth ground needed, from outside it is needed.

 

PS to Lou: Aren't you due into Escapade today?

Good travelin !...............Kirk

Full-time 11+ years...... Now seasonal travelers.
Kirk & Pam's Great RV Adventure

            images?q=tbn:ANd9GcQqFswi_bvvojaMvanTWAI

 

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Morning gang, its a rainy day here in Indiana and I was supposed to get the RV waxed...I'm using Meguiars ? Cleaner Wax then later Collonite 845 Wax Insulator, anyone used that combination???????????????????

 

 

Mn Tom

 

"John, I hate to say it, but I completely understood everything you said about grounding"

 

THANK YOU I try my best to help and glad you "completely understood" everything I said HOWEVER why hate to say it ??????????????? lol that's the very reason I spend time trying to explain things in detail LOOKS LIKE IT WORKED TOO !!!!!

 

"It is actually surprising the number of individuals that don't grasp the difference between grounding and grounded......"

 

SOOOOOOOOOOOOO true as I found in over 40 years or practice, but I do my part to help, it may save someone's life. HOWEVER just as "individuals" may not grasp the difference, that's NOT a bad thing regarding them, most individuals don't grasp the difference when their Doctor explains things to them either !!!! Different strokes and different areas of expertise among different folks out there.

 

 

Lou,

 

 

"If the RV's power source is totally isolated from ground, it doesn't matter if the RV is grounded or not. The voltage is not ground referenced, so there's no way it can deliver a shock to someone standing on the ground. Just like a bird can land on an energized power line and not get shocked."

 

GOOD POINT that's why NEC and OSHA don't require earth grounding of portable construction gensets ( It can even "create an electrocution hazard" ) that serve plug and cord connected tools fed from onboard receptacles. If you come in contact with a hot wire and are on wet ground AS YOU UNDERSTAND THERES NO VOLTAGE REFERENCE TO MOTHER EARTH

 

"BUT, if the power source has any connection to ground (i.e. utility power) then the RV must also be grounded to keep stray voltage from leaking to it's frame and skin. Since the voltage is ground referenced, it will flow through any path that comes between the RV and ground. If that path happens to be you when you touch the skin of the RV, you will get a shock"

 

ALSO A GOOD POINT and to add just a bit, its being in contact with the Utilities Equipment Grounding Conductor affords a low impedance current return path so if a hot shorts to the RV frame the circuit breaker will trip and clear the fault and can save your life!!!!!!!!!!!!

 

 

Great thread, I hope 4 x 4 understand and this helped him???????? What a fine group of gentleman here and I'm glad to be a member and help anytime I can.

 

God Bless yall

 

John T

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Best wishes Steve, glad you feel "enlightened" and don't feel bad, the vast majority of non electricians and non engineers, plus even many professionals get CORNfused about "Ground",,,,,,,,,and Earth Ground,,,,,,,,,,,,and GroundING Conductor,,,,,,,,,,,,,,and GrounDED Conductor,,,,,,,,,,,,,and GroundING Electrodes,,,,,,,,,and Bonding and Grounding. I try my best to help and will continue to do so.

 

Yall take care now, keep safe and happy travels, God Bless

 

John T

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