Soooooooo, hey there John T

glennster

Well-known Member
O great exalted one, and master of the electron.....one of your grass hoppers has a question. (see, i buttered ya up pretty good!!) .
is there any difference in gounding/neutral sequences when say you have a motor home in an campground, where you pull in and maybe run a generator, then plug the rv into campground "shore"power. i would assume the rv is electricallly insulated via the tires, up until the point leveling jacks were dropped into the ground, or say an awning was erected and the poles then touch mother earth. or another example is a boat docking at a marina, then plugging in to shore power to run a/c units, battery chargers, microwave, water heater ect. the boats propulsion system being in the water, would also become a mother earth ground. would these follow a similiar proceedure like from a main distributon panel to an out building sub panel where the neutral and ground are not bonded in the sub panel but both return to the main panel? just wondering if a hazard exists and how they deal with it. kind of like you see on the news where someone steps on a metal grate on the side walk or leans against a street lamp post and gets electrocuted. ( happened in chicago several times) just wondering.... thanks.
 

Not John T.
Many RVs are only 120 volts. These have a Green Ground wire/conductor, a white/neutral wire, and black/hot wire.
The green wire attaches to the steel frame of the RV. Only when this wire becomes broken from the shore or the RV frame is there a problem.
There are some RVs that have 240 volt, but they still have a ground wire.

Dusty
 
Flattey will get you SOMEWHERE LOL

On typical 30 amp 120 Volt Motorhomes, that's only 120 VAC single phase, One Hot UnGrounded Conductor, One Grounded (Neutral) Conductor, One Equipment GroundING Conductor. NEMA TT 30

Inside the RV's AC Distribution Panel the Neutral Buss is isolated and insulated from the Equipment Ground Buss, while the metal case/tub/frame is bonded to the Equipment Ground Buss as well as the RV Frame.

On a 50 amp 120/240 volt (larger MH, maybe two AC units) there's two Hot L1 & L2 Ungrounded Conductors (240 VAC across ),, A Grounded Conductor (Neutral), and again the bare/green Equipment GroundING Conductor. Also Neutral and ground are again separate and isolated and insulated.

THE RV FRAME/CHASSIS IS BONDED TO THE EQUIPMENT GROUND BUSS

OKAY, I have to run to Square Dance lessons, were teaching new members on Tuesday nights, but I will answer your other questions when I return.

Its a good question and a valid concern, I will be back later. My friend the good Dusty man as well as several other qualified trained professional electricians are on here to help PLUS I'm sure Billy Bob and Bubba will toss in their two cents worth.

Back later, gotta run for now

John T
 
Back from squared dancing: I already described how they are wired, so heres more info.


"is there any difference in gounding/neutral sequences when say you have a motor home in an campground, where you pull in and maybe run a generator, then plug the rv into campground "shore"power"


Answered below, the RV frame/chassis is bonded to the Equipment Ground Buss so if a hot wire got shorted to it theres a low impedance fault current return path to clear the fault....

" i would assume the rv is electricallly insulated via the tires, up until the point leveling jacks were dropped into the ground, or say an awning was erected and the poles then touch mother earth."

The RV frame is bonded to the equipment ground buss in the RV panel. True it may be somewhat insulated with respect to mother earth subject to jacks or awning supports etc. which would help bring it back down to local earth potential.

"would these follow a similiar proceedure like from a main distributon panel to an out building sub panel where the neutral and ground are not bonded in the sub panel but both return to the main panel?"

It similar in that the Grounded Conductor (Neutral) and Equipment Grounding Conductor (isolated at a sub) are both wired back to the main panel


"just wondering if a hazard exists and how they deal with it"

They deal with it by having the RV frame/chassis/skin etc bonded to the Equipment Ground Buss so if a hot shorts to it the grounding conductor carries fault current back to the panel so the breaker trips


"kind of like you see on the news where someone steps on a metal grate on the side walk or leans against a street lamp post and gets electrocuted"

If the street lamp post was properly bonded to the Equipment Grounding Conductor and a hot shorted to it, the fault would have been cleared.


Nuff said, don't be afraid or hesitant to use proper and safe grounding, ground rods are NOT your enemy a some lay people seem to think.

Hope this helps

John T
 
Glennster,
Not John T, I waited until he was done. I respect him too much to step on his shoes!
As an antidotal item, one of the local fairgrounds requires the campers that park there to put in a ground rod that is tied to the chassis of the camper. Rod only needed to be 4 ft. So the campers would buy a 8 foot rod and cut it in two and share with their buddy.
I went to buy a ground rod when they first enacted this rule and the local Home Depot had run out of rods.
I believe they enacted this rule because of a lightning strike that happened the year before. So like some NEC rules, someone had to have a bad experience in order to bring about this change.

Keith
 


When your on your genny power.. the "return" is to the onboard generator, so the danger of walking up and getting shocked when touching the outside is negligible.

When your on shore power... everything changes as its looking for a ground return and you dont what to be part of that circuit.

So the cord has a ground, and the motorhome will have lots of ground fault plugs. Assuming the cord and grounding system is good, the motorhome should be at ground potential as all times.

If you have an external generator sitting on the ground. things can change again, pending on how the generator neutral is set up.
 
I've not been to any such campground, but hey when in Rome do as the Romans do I guess (especially if you cant camp there otherwise). As far as the NEC, many of its changes and additions have come about because someone was killed or a building burned down. Some poke fun at the NEC panel of experts and their advice figuring they know more about electrical safety I guess, but there exists a possibility ignoring the rules might endanger their lives. YALL DO AS YOU PLEASE and even some local inspector can get it wrong, but he rules and NO ELECTRICITY until he says so lol

As far as posting, in my opinion peoples postings and stories and experiences and antecdotes have value and I enjoy them all. So often one person has a product or method and claims it worked perfect while the very next poster has the exact opposite story where something didn't work at all lol. And I'm sure not going to call either one a liar, I'm here to help, not fight or argue.

Feel free to step on my toes before or after and add comments anytime anyplace. NO ONE (sure includes me) is perfect, we all make mistakes including me, all inputs are appreciated by me at least. I'm long retired and rusty, while there are several currently active and practicing electrical engineers and technicians and professional trained electricians here who are sharper on this then I am, but hey I help as much as possible. Also wouldn't it be a boring world if we all had the same opinions or methods or preferences or way of doing things lol. As far as I'm concerned, it shouldn't be MY WAY OR THE HIGHWAY HERE as some might think or prefer.

PS Earth Grounding can help as far as surges and lightning strikes are concerned. However what's very important is any outer conductive metal skin/case/frame of an appliance or a metal light pole or a tool or an RV etc have a bonded Equipment Grounding Conductor to clear the fault in case a hot short to case happens YIKES.

Take care and KEEP SAFE

Best wishes n God Bless all here

John T
 
"If you have an external generator sitting on the ground. things can change again, pending on how the generator neutral is set up"

Indeed, some small portable Gensets have a Floating Neutral while others may NOT. Somewhere I saw a list and models which had which.

A genny may be configured as a Separately Derived Source or not, which makes a difference as to how many poles a transfer switch must contain and Neutral bonding.

In cases where plug and cord connected tools are powered direct by onboard mounted genset receptacles, a Grounding Electrode isn't NEC required. (at least when and where I practiced but NO WARRANTY TODAY AND WHERE YOU MAY BE)

There's lots lots more, but nuff for now, good post and fun chattin with ya

John T
 
JohnT. Are travel trailers like mobile homes? Does the metal on a travel trailer needs to be grounded? A few years ago a local was electrocuted because the metal siding on his travel trailer was hot. It was sitting in his back yard running off an extension cord. George
 
Not sure of all your questions George, other then, if the frame and any metal or siding or any potential current carrying conductors are bonded to the Equipment Ground Buss, if a hot short were to develop fault current would have a return current path so the breaker trips and clears the fault. The hazard is where a hot shorts to the frame or case or metal shell and it stays energized so when little barefoot grandson Johnny touches it HE MAY GET KILLED.

John T
 
My question is, Does the metal siding on a travel trailer, like the metal siding on a Mobile home, have to be grounded? If a generator is applying 220v to a travel trailer, then do you use a 4 wire cord and use a grounding rod?
 
George, I see the frames definitely grounded, but not individual pieces of metal siding. That's not to say the metal may not be in electrical contact somewhere somehow with the RV's frame, depends on mounting and attachment methods and fasteners etc. etc.

YES in larger RV's (often have two roof AC units) that use those 50 amp 120/240 volt plugs and receptacles, they are indeed 3 Pole 4 Wire Grounding Receptacles and Plugs, That's Two Hot Ungrounded Conductors, One GrounDED Conductor, One Equipment GroundING Conductor.

Always nice chattin with ya Neighbor

John T
 
John T,
This is in reference to the street lamp post shock. I saw this on TV in the last couple of weeks, a piece on today show (see ulr). This will open your eyes. In MY own experence I have seen THIS. Was sent on a call of people getting shocked in an inground pool when they touched the ladder while in the pool. I looked at everything related to the pool pump/filter/ lighting-- everything!!! could not find where the shock was comming from... I measured around 100 + or- from water to service ground. Even after turning the MAIN breaker off , still had the 100 volts!
The problem turned out to be an old 7200 volt underground feeder to a pad mounted transformer serving several homes in the subdivision. It was an old feeder braking down from age, much like in the rossen report.
As far as I could see the pool and equipment met all grounding / bonding rules.

Back to you John , joe
Rossen reports
 
I know of a person who ran a screw from the outside of Mobile home into a wire. The trailer siding was grounded and melted the tip of screw and blew a hole in wire. Travel trailers are on rubber, so that may expain why a local got fried when he touched the side of camper, no ground.
 
Yep, if the RV had what's called a HOT SKIN due to a hot wire shorted against it (or some other set of circumstances) and there was no fault current return path (no equipment grounding conductor) allowing sufficient current to trip the breaker and clear the fault, and you touched that hot energized surface YOU COULD WAKE UP DEAD..

John T
 

Although not as likely it could also happen on a steel sided building. So with one of the newer code changes, bonding/grounding the steel siding, that should not happen.
I say should not because it's only a friction fit of each sheet of steel and perhaps the continuity could be lost between sheets.

Dusty
 
a neighbor of mine had a problem with getting shocks when opening his front aluminum door at his house. discovered someone put the light switch on the neutral instead of the hot. the outside fixture was mounted on the aluminum siding.
 

Neighbour had one generator that would operate his camp trailer but the other generator would trip it's GFI on the same trailer.
The tripping generator had an internal grounded neutral conductor and the trailer had a bonded neutral in it's panel. The flow of neutral current on the ground system was tripping the gfi.
 

This is where ground rods are supposed to be driven everywhere AND everything metallic bonded together . To obtain a common ground plain by interconnecting all ground rods, water pipes, well casings, building metal etc. one local ground rod on it's own can not hold the voltage down to a safe level during a fault.
 

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