Grounding while using a generator

[lostagain]

Following the other generator thread brings this question.

The bus is grounded to the grid through the pole when plugged in, because the neutral wires are isolated from the ground conductors. I understand that part.

When the bus is plugged in to the generator, is it not grounded to anything?

I use a cheap (OMG!) portable unit set on the ground. Should I drive a grounding rod in the earth to ground it?

I don't understand electricity very well.

JC

[cody]

.

[bevans6]

My generator's manual suggests a suitable grounding rod and conductor to ground the generator and hence the bus, yes.  Also many generators do not bond neutral to ground, they float neutral.  Neutral is supposed to be bonded to ground at the source, which is the generator in this case, so I don't know why some generators do not bond neutral.  I would love to know the reasoning behind that.

Brian

[Van]

I am Gonna have to pay attention to this very carefully, I am currently faced with this challenge at this very moment. I have removed the Ac condensor/fan and, which is where my EM5000x is located now.

[john9861]

Van,
      This is the spot where I get tripped up some too. I'm hoping the experts say that the generator grounds to the chassis & the neutral is still isolated(floating). Let's see what they say. Where are you Sean?

[BG6]

There are a couple of different things that we call "ground" -- there is the chassis ground, which EVERY electrical device in the coach should share, and there is GROUND, which is to the planet.

They are two kinds of the same thing -- a zero-potential connection between things which may have their own electrical charge.

If you have ever noticed a strap dragging the ground under a police car, or seen a few links of chain swinging from the brake arm on a school bus, these are both ways to ground the vehicle to eliminate the static electricity charge that builds up while driving.  The cop car uses a "static strap" to improve radio reception, and the bus chain drops to the ground when the park brake is set, so that they don't shock passengers getting on, then is pulled high enough to not hit the ground when the brake is released.

This is why you are required to take gas cans out of the vehicle and set them on the ground to fill them (it's also a good idea to set them on the ground before emptying them) -- the can may have a charge, while the fuel nozzle is grounded.

The more ground, the better.  When I camp, I have a steel spike driven into the ground, and a big alligator clip hooked to it that runs to the coach chassis, thus to every device in the coach, whether it is on the solar, the generator or line power (depending on where I am).  When at the airport I fly from, I hook that alligator clip to the hangar I park next to.

The bottom line is that EVERYTHING in the coach needs to be grounded to your frame, and though not necessary, it doesn't hurt to ground that frame to the planet.

[PP]

BG6, you sound like a very well grounded individual, LOL (couldn't resist)

Will

[Sean]

... Where are you Sean? ...

I'm in my den, licking my wounds from the other thread.  Seriously, I'm at a conference and I have limited time to read and post here.  Let me try to help out:

As you have already noted, RV 120-volt electrical systems intended to be connected to shore power, by code and safe practice, must have the ground and neutral separated aboard the RV.  That's because they are connected together in the shore system, usually at the transformer.  If they were also connected aboard the RV, then a good portion (more than half) of the return current will be carried on the ground, including the vehicle chassis, instead of the neutral.  This will energize the vehicle frame, creating a shock hazard.  That's if everything else is wired correctly; if there happens to be a hot-neutral reversal someplace, such as might occur with one of those two-prong adapters, then things can get much worse.

Simple enough so far.  Adding a generator to the mix, however, also adds complexity.

Vehicle-mounted generators that are designed and listed for that application, as discussed hotly debated in the other thread, will have ground and neutral bonded inside the generator.  There will also be a lug on the generator where it is to be bonded to the vehicle frame.  If you use a simple receptacle on the generator into which the shore cord is plugged, the simplest connection method, then all will be exactly as if a shore connection was used.  There will be a single ground-neutral connection in the generator, all current will return to the generator on the neutral, and any fault to ground will cause a breaker trip.

If you instead use a transfer switch, whether automatic or manual, you will need to select a model that can switch the neutral along with the hot wire(s).  This assures that when connected to shore, the ground-neutral bond is in the shore system, and not on board the RV, yet when connected to the generator the bond is in the generator and not in the shore system.

Portable generators create a different problem.  Some have ground-neutral bonding internal to the generator, and these are fine to use as-is.  There is no need to utilize a "driven ground" unless you are also using portable electric equipment outside the rig.  However, some units, particularly those that are sold or intended for home backup power purposes, will not have this ground-neutral bond present.

This latter type is dangerous to use to power an RV, which is one of the reasons why I urged caution in the other thread.  If there is no ground-neutral bond at all, then "fault current" has no way to return to the neutral lug in the generator and thus the circuit breakers designed to protect personnel and equipment may never trip, even if deadly current is traveling through a person to the vehicle frame.

One way to deal with this is to consult the generator manufacturer's instructions or support department to find out if there is a way to implement the ground-neutral bond inside the generator frame.  Many generators have an option to do just this, usually by connecting two terminals together inside the generator's junction box with a strap or jumper made for the purpose.

If that method is not available, and you must use the generator anyway, then you can implement the ground-neutral bond in a dedicated pigtail used to connect the generator to the shore cord.  This pigtail should be clearly labeled as having ground and neutral bonded and preferably would not have a male connector that can mate to conventional shore receptacles.  Note that this method carries some inherent risk and should be considered "temporary" only.

Here again, there is no need for a "driven ground" so long as no equipment is being operated outside of the rig itself.

In the long run, you should seriously consider upgrading to a listed RV-type generator with proper grounding and bonding for permanent installation.

-Sean
http://OurOdyssey.BlogSpot.com

[Van]

Thanks Sean, I have come to learn of this isolated ground in the past few days, but now I know why thanks again

[RTS/Daytona]

This article is very helpful--> http://www.fmcmagazine.com/Images/stories/pdf/ac_safety.pdf

[john9861]

Thanks RTS/Daytona (Sorry don't know your name) for posting the article. I had saved that one which is very informative but I didn't realize it was available online.
  Van, That article explains it very well.
  Sean, Thanks for kicking in. I wanted a second opinion for comparison to the article.
I'll be hooking up all my house electrical very soon & wanted to only have to do it once.
BG6, Thanks for the info on the grounding of vehicles with strap or chain. I've been wondering how to get rid of that zip I get every time I touch my Ford Expedition. I've got plenty of fingerprints on the driver's window from using it to close the door instead of the HELLO you get when least expected!
Thanks again guys.

[zubzub]

Thanks Sean.....I had not started on my  gen thing yet and was unclear about the bonded unbonded ....it now makes sense and I didn't really need to think hard about.  Very clear and concise.

[Chopper Scott]

Several years ago we had a terrible ice storm which led to devastating damage to the electrical infrastructure in our area and the only power option we had was generators. I also had several portable welders also that made electricity. What everyone was doing was running power to the generator to any 220 volt hookup (dryer, outside condensor, and such) and backfeeding it into the house. It worked really well but you had to watch your power usage and naturally shut off your main switch. On several occasions I heard stories of someone not grounding the generator to earth ground and if it blew a breaker on 1 leg the generator would throw all the power into the other leg and they burned out anything running on that leg at the time.

[lostagain]

Thand you Sean for spending the time to write your answer. Very good. I will look at my gen today to see if neutral and ground are bonded.

JC