RV Electrical Grounding....

For the Electricions out there; What is your opinion about running an electrical ground wire from the RV chassis to earth?  I realize that when my rig is plugged in to shore power, we are grounded thru the service (hopefully).  What about when running the GEN and we are not on shore power?  I know the GEN is grounded to the chassis, but not to earth.  For safety wouldn't it be best to always run a ground wire to earth when parked?  Just short of pounding in an 8' grounding rod everywhere I go, what would be the best way to ground to earth?  I thought about maybe parking our rig on a steel plate (between a tire and earth) and attaching a ground wire from the chassis to the plate.  Your thoughts?  Am I concerned about nothing?

Thanks!

The purpose of using a ground rod on a service is for lightning protection not to handle fault current, the ground wire is bonded to the neutral at the point of service so fault current has a good solid low resistance path back to the point of generation. The ground rod will provide a path but it will be high resistance and vary depending on the moisture in the soil, the ground rods most important job is the help with lightning protection because the point of generation is the earth not the generation plant. When you are running your generator it is the point of generation so the ground wire and frame should be bonded to the neutral at that point. When you are shore power the separate ground wire not neutral will go all the way back to the point of service where it's bonded to the neutral and ground rod for a good fault current path. So no you don't need a ground rod unless you are worried about lightning and then you don't want to be the best ground around anyway, your tires are good insulators and just put plastic or wood pads under your stabilizers to help isolate the rig from the ground and enjoy your RV trips.

Denny

Actually the National Electrical Code (NEC) likes to have an electrical subsystem (which would include an RV) bonded to ground via the feed, which is the shore power line in this case. However, they do make some exceptions for farm/barn wiring an such, so the definition of the "right" answer for an RV could be argued.

When using a portable generator, a local ground rod MAY be recommended in some situation but generally is NOT. See the OSHA article below for a summary - much easier to read than the NEC. The generator installed in a motorhome is not really portable, but it does meet the OSHA requirements by having everything grounded to its chassis, so no earth ground is required.

Bottom line is that you need not worry.

http://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf

Are you using a portable genset in the toyhauler or is it factory-installed?  If factory installed, it likely meets the requirements of NEC and OSHA for generator wiring. The RVIA standards cross reference to the NEC for electrical wiring.

There are a lot more reason to have a ground wire going to a ground rod than just lightning. All metal parts to electrical machinery are bonded to the ground in case of an insulation failure then the voltage will go to ground and trip the breaker rather than being live and potentially killing someone. A ground wire also helps prevent the buildup of static electricity.


Gary is right, bottom line is you have nothing to worry about.

Re: For safety's sake wouldn't it be better to run a grounding wire to earth"

First, Usually the generator is NOT grounded to the chassis on the 120vac side (it is on the 12 volt side though)

And no, it would not be safer.. In fact it's more dangerous.

here is why...

In the old days tools often had 2-wire plugs, Hot/Neutral if used in a home.. but if the tool, say a Skill hand grinder, developed an intermittent short "hot" to Case, well it could give you a fairly good shock.. Why?  Because of history mostly.

Back in the days of world wars, Copper (And even aluminum) were expensive.. So they grounded the low-tension system at the transformer pole.. And ran but a SINGLE 120 volt wire to the house.. They used the earth itself as the return to the transformer.. This saved them 1/2 the cost of the heavy duty drop wire.

Today they still ground at the pole. and at the service entrance to the house.. So neutral and ground are bonded together.

Thus when that hand grinder shorted out.. My arm convulsed and shattered the grinding head (Did I mention I used that grinder).. I tried wearing gloves but that did not work well in that shop. SO I bought my own hand grinder and ... Well it lasted 20 years before it wore out. (A Dremel hobby grade unit.. PLASTIC case)

So, now days devices often come with a 3 wire plug.. Should you get a Hot-Case short. the ground wire takes the current and trips the breaker. (Beats Cardio-Pulmonary Resuscitation)

But what would happen if you slapped an ISOLATION transformer between the outlet and that Skill grinder that tried to knock me on my pride?

The answer is when the short happened. there would be no return path for the current, and no shock to the user.

I know. I use isolation transformers too

IN short. it was the presence of a system ground that enabled it to shock me.

Thus, from a safety standpoint.. Ground on the motor home is not an improvement in the 120volt system.

OH, the Green wire.. That is grounded to the frame, but you may well find 60 volts (At next to zero current) between white and green, or between black and green since both white and black, from the generator, are "hot" Neutral in a 120 volt single phase system is meaningless, there is none.

In a 240 volt center tapped system (120-0-120) the center tap is called "Neutral" because of it's relation to the two end taps (L-1 and L-2)

And that is the one they ground.

But not on a generator.

That's the 120vac side of life

Now we get into other stuff.. Like static electricity and RF and son on

Here a good ground is handy...  A ground can prevent static, Imagine hooking or unhooking a propane line and suddenly there is a spark from static electricity build up on the rig.. Not good

A ground (either independent or the service if plugged into shore power) prevents that

And at RF.. The service ground may or may not be good.  But setting up a 2nd ground is usually bad.

seilerbird said:

There are a lot more reason to have a ground wire going to a ground rod than just lightning. All metal parts to electrical machinery are bonded to the ground in case of an insulation failure then the voltage will go to ground and trip the breaker rather than being live and potentially killing someone. A ground wire also helps prevent the buildup of static electricity.


Gary is right, bottom line is you have nothing to worry about.

Click to expand...

The grounding conductor (green or bare) provides a path for the fault current (insulation failure) back to the neutral where it's bonded along with the ground wire that is attached to the ground rod. The neutral is the least path of resistance to the point of generation not the high resistive ground rod so the fault current will flow on the service neutral.

Gary the NEC does have a exception for farms mostly in milking parlors and confinement buildings because of the low resistance of farm animals and the harm stray voltages can cause to the animals so there are some special grounding and bonding that has to be done but that exception applies to farms only and does not apply to anywhere else.

John From Detroit static and RF is a hole different argument that there is no good answer for, I wired a few electronic switch buildings for a phone company and they had some very interesting ways to try and solve the problem, some of the grounding and bonding methods they used did not comply with the NEC but my inspector let it go because he knew what they where trying to accomplish to try and protect their equipment and it was safe but they did set up a better earth ground than the power company had so we get back to the path of least resistance for lightning and other stray voltages.

As far as static electricity and propane and fuel tanks in vehicles we started to see more fires because the fuel systems have better bonds to ground even the fuel hose have a bonding sheath in them. So if you don't touch the vehicle before you begin fueling you can create a static spark when the grounded fuel hose comes close to the tank and causes a static spark that may cause a fire because of the path of least resistance to ground. If you want so interesting conversation get a Fire Marshal and a Electrical Inspector in the same room talking about static sparks and fuel systems.

Denny       

       

Basically, it depends on whether the source of power is connected to ground or isolated from ground.

It's impossible to isolate the entire electrical grid from ground, so it's tied to ground in numerous places including at the main circuit breaker panel (the one immediately after the main electrical meter).  Since the source of power is tied to ground, you can get current flow from the hot side of the circuit through ground back to the source.  If you get between the hot side of the circuit and ground, part of the current will flow through you and you'll get a shock.

The point is you have to become part of the current path back to the source to get shocked.  With a grounded source, ground is part of the path so you can get shocked if you're touching a voltage source and ground.

If there's no ground path back to the source, no shock hazard exists between the voltage source and ground.  It's like using an isolation transformer on commercial power.  Shock hazard exists between the hot and neutral leads, but not from the voltage to ground because the source is not connected to ground.

An ungrounded RV (or portable) generator is isolated from earth ground, so it acts like an isolation transformer.  Since the power source is isolated, there's no way for part of the current to flow back to the source through the ground and there's no shock hazard from the voltage to ground.  It's the same principle that lets a bird land on an energized 12,000 volt power line - as long as there bird is isolated from ground, no current flows through the bird and he isn't harmed.

Lou's explanation is clear, correct & right on the money. If you are interested in a more technical description of the pros & cons of grounding generators (and RVs), check this Generator Grounding PDF.

Lou is correct with one exeption, the generator on an RV does genereate not only electrostatic, but also genereates EMF (Electromagnetic Filed) around any metal attached to chassis. Simple way to find out, is by running your Genny and a light source (load). Then outside the RV, remove your shoes and socks, get them wet (like when you are at the beach). While getting in the RV, more than likely you are going to have one foot on the ground and one on the steps at the same time your hand is on the handle of some sort. If any of those are attache to the chassis and they are metal, then you will get shock. I usualy have a 10gauge wire with an awning anker to stick on the ground while at the beach to avoid that.

Excellent information everyone..... THANK YOU!  It looks like I am overthinking again (it's a blessing AND a curse).  Anyway, I really appreciate the help.  I am not going to worry about grounding my rig.  As I now understant this, about the only way I MIGHT have a problem is IF the supplied shore power was not grounded properly AND if I had a short somewhere within my trailer (IE; the frame was electrically HOT) then if I were to touch the rig while standing on earth I'd get a shock (how much of a shock would depend on how well I was grounded to earth.... IE; wet shoes = good earth ground = ZAP!).  I do use my mulit-meter to check campground shore power to be sure the hook-ups are wired correctly BEFORE I plug-in.... I have not yet found a problem (however, I have only been to about a half dozen campgrounds so far).  Again, many thanks!   

If you use a powerline monitoring system like the Surge Guard , it will check for a number of shore power faults, including an open ground.    Examples include high & low voltage, reversed hot and neutral, open ground, and reversed neutral & ground. While not strictly necessary, these monitors will protect you and your equipment from a variety of electrical faults.

http://www.surgeguard.com/index.html

Fred G. said:

Lou is correct with one exeption, the generator on an RV does genereate not only electrostatic, but also genereates EMF (Electromagnetic Filed) around any metal attached to chassis. Simple way to find out, is by running your Genny and a light source (load). Then outside the RV, remove your shoes and socks, get them wet (like when you are at the beach). While getting in the RV, more than likely you are going to have one foot on the ground and one on the steps at the same time your hand is on the handle of some sort. If any of those are attache to the chassis and they are metal, then you will get shock. I usualy have a 10gauge wire with an awning anker to stick on the ground while at the beach to avoid that.

Click to expand...

What you are describing is a capative voltage divider.. The white and black wires running side by side with the green wire form a very low value capacitor, this "Divides" the voltage between them so you get 60 volts.. however due to the very low value of the capacitor you get nearly no current.  I do admit, when I get working on the breaker box with sweaty palms it does tingle a bit.. But more annoying than dangerous.  Not enough to trigger a spasm response.

(Trust me... I've been bit by the kind of current that DOES trip a spasm response, more than once, hazard of working in electronics.. 120 volts bites hard, 500 can dim your lights)

I'm a used motor home owner, but a new RV'r. If I'm bare footed and touch my coach when it's plugged in, it gives my an annoying shock. What could it be?

Chuck Scanlon said:

I'm a used motor home owner, but a new RV'r. If I'm bare footed and touch my coach when it's plugged in, it gives my an annoying shock. What could it be?

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Probably a short between neutral and ground in the motorhome.  More rarely you might be plugging into an outlet where neutral and ground are reversed or where someone didn't run a ground wire and just used neutral for that.

Just to add to Jammer's response, in a motor home or trailer the Neutral wires may have been intentionally bonded (connected) to ground (the coach framework usually) within the coach. This should never be done but sometimes is.

I think the most likely place for that to happen is likely behind the main circuit breaker panel. Check that there are no strange wires on the same buss bar as the neutrals (white wires). Each neutral should pair up with a black wire from behind the breakers. Any orphans need investigating...

There's quite a bit of misinformation in this thread.  For OSHA requirements for connecting a portable generator that is used to provide power to an RV or trailer, please consult and carefully read the following document:
https://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf
Yes, it is an OSHA requirement to connect the chassis of a portable generator, that is used to provide power to an RV or trailer, to an appropriate earth ground.

On a related subject, when powering your RV from a campground pedestal, you want to make absolutely certain that the outlet on the pedestal is wired correctly.  If you don't know how to do this, then purchase one of the many commercially available AC outlet wiring testers.

AreCF said:

There's quite a bit of misinformation in this thread.  For OSHA requirements for connecting a portable generator that is used to provide power to an RV or trailer, please consult and carefully read the following document:
https://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf
Yes, it is an OSHA requirement to connect the chassis of a portable generator, that is used to provide power to an RV or trailer, to an appropriate earth ground.

Click to expand...

That is not my understanding of OSHA rules per the attached document. Read it again.

In my opinion, the poster did not correctly interpret this OSHA document:
Details:
Grounding Requirements for Portable and Vehicle-mounted Generators Under the following conditions, OSHA directs (29 CFR 1926.404(f)(3)(i)) that the frame of a portable generator need not be grounded (connected to earth) and that the frame may serve as the ground (in place of the earth):
? The generator supplies only equipment mounted on the generator and/or cord- and plug-connected equipment through receptacles mounted on the generator, ? 1926.404(f)(3)(i)(A), and
? The noncurrent-carrying metal parts of equipment (such as the fuel tank, the inter?nal combustion engine, and the generator?s housing) are bonded to the generator frame, and the equipment grounding conductor terminals (of the power receptacles that are a part of [mounted on] the generator) are bonded to the generator frame, ? 1926.404(f)(3)(i)(B).
Thus, rather than connect to a grounding electrode system, such as a driven ground rod, the generator?s frame replaces the grounding electrode.
If these conditions do not exist, then a grounding electrode, such as a ground rod, is required. (These conditions do not exist when powering an RV from a generator.)

Chuck Scanlon said:

I'm a used motor home owner, but a new RV'r. If I'm bare footed and touch my coach when it's plugged in, it gives my an annoying shock. What could it be?

Click to expand...

You have an open ground to the shore power system. It is normal to have a hot skin (less then 60 VAC) if the chassis is not connected to the shore power source ground.

If you understand why Grounding is important when plugged into the power Grid (mains power) You understand why it is NOT necessary or possibly even desirable when using a portable generator or inverter.  And again why it is needed in a Home "Standby" Generator (the kind that are NOT portable).

Strangely,,, the people who wrote the code... Seem to understand these things.. As the code reflects said understanding.. Very odd indeed when it comes to rules and regulations (ok, Actually not at all that odd).

I truly do not have the time to explain it all here.. yet again.  But the short version is the safety ground is there to protect you in the event of a hot-case short on a hand tool or device..  IN a home/office/business enviorment such a short can be SHOCKING so the safety ground pops the breaker to protect you    BUT if the GROUND is not connected to the power source (the Mains are Grounded) then there is no path for power to flow THROUGH YOU and even if the hot wire is connected to the case.... The tool works normally.. You never feel a thing shock wise.