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Thread: Grounding a portable generator

  1. #1
    DIY Member Cubey's Avatar
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    Question Grounding a portable generator

    I plan to occasionally use a portable generator (about 3500w or so in case it matters) when boondocking (camping off the grid) with my travel trailer. Typically proper ground rods are 8ft however, trying to install an 8ft ground rod for temporary use of perhaps only a few days would be highly inconvenient and then I would also have to attempt to pull it up when I'm finished which might be impossible. Plus I would have to store the 8ft metal rod someplace when traveling. Most inconvenient that would be on so many levels (driving it in, removing it, storing it).

    I have found mentions online about using two 4ft rods connected together and spaced 5 feet apart from each other for antenna grounding is almost as good as a single 8ft rod. Two 4ft rods would be much easier to drive into the ground and remove than a single 8ft rod would be, as well as store when not in use.

    So my question is: Would two 4ft rods linked together with 12 gauge wire and spaced 5ft apart be adequate grounding for a portable generator?

  2. #2

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    Save your strength.

    250.34 Portable and Vehicle-Mounted Generators.
    (A) Portable Generators. The frame of a portable generator shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by the generator under the following conditions:
    (1) The generator supplies only equipment mounted on the generator, cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
    (2) The non–current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.
    (B) Vehicle-Mounted Generators. The frame of a vehicle shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by a generator located on this vehicle under the following conditions:
    (1) The frame of the generator is bonded to the vehicle frame, and
    (2) The generator supplies only equipment located on the vehicle or cord-and-plug-connected equipment through receptacles mounted on the vehicle, or both equipment located on the vehicle and cord-and-plug-connected equipment through receptacles mounted on the vehicle or on the generator, and
    (3) The non–current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.
    Just my 2 worth.

  3. #3
    DIY Senior Member BrianJohn's Avatar
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    To simplify 480's post not required, not necessary and would gain you nothing.

  4. #4
    DIY Member Cubey's Avatar
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    As I understand it, most generators have neutral and ground bonded to the frame of the generator and therefore must be grounded.

    The generalized manual for all Coleman generators says this:

    BEFORE OPERATION - GROUNDING THE GENERATOR
    The National Electric Code requires that this product be
    properly connected to an appropriate earth ground to help prevent
    electric shock. A ground terminal connected to the frame of the
    generator has been provided for this purpose. Connecting a length of
    heavy gauge (12 AWG min.) copper wire between the generator
    Ground Terminal and a copper rod driven into the ground should
    provide a suitable ground connection. However, consult with a local
    electrician to insure that local codes are being adhered to.

    --
    Source: http://www.colemanpowermate.com/gene...ors_manual.pdf
    Someone I talk to online who states that he is certified to do RV repairs (so that means he knows a lot I guess) or some such says that he witnessed someone using an ungrounded generator in a campground when a I little girl selling donuts came up and knocked on the guy's door and was electrocuted because the generator wasn't grounded and caused the trailer's ground (chassis) to become hot and somehow prevented the GFI on the generator to kick off because of a lack of proper ground.

    The following is from: http://www.jackssmallengines.com/generator-safety.cfm

    How about grounding?
    Don't worry you say? Oh, you bought an expensive generator that is equipped with a GFI (Ground Fault Interrupter). Well did you know that a GFI might not function at all if the generator is not properly grounded? Recently we had a customer bring in a new generator for service. He should have bought a lotto ticket that day. His generator had an internal short circuit that made the handles on the unit electrically charged (hot as we say). Had he touch the wrong two things, at the same time, it could have killed him.

    Do not use that generator until its been safely ground.
    Grounding is simple, refer to that owners manual. It would most often tell you to attach a #8 copper wire to: a metal water pipe that travels at least 10 feet into the ground, hook to a building ground, or drive a metal rod 8 feet into the earth, etc. Make sure you use a rod that is permitted for grounding. There are minimum sizes and material that will give you the proper grounding.

    However according to this page.. http://www.imsasafety.org/journal/marapr/ma5.htm

    Portable generators are often used for backup power at traffic signals, buildings, structures and special events. Ground rods (grounding electrodes) are only required if the generator is a separately derived system. (For the complete text of sections cited please see the 2002 NEC)

    The key to knowing if a generator is a Separately Derived System is not the generator, but rather the transfer switch. If the transfer switch does not transfer the neutral (grounded conductor), then the generator has a “solidly connected” grounded circuit conductor and the generator is not a separately derived system. [See Fig 2]
    If you refer to Fig 1 vs 2 on the page, you will see that 1 has ground/neutral connected to each other (usual practice on portable generators) where as 2 shows them separated. According to that page, a portable generator with bonded neutral/ground to the frame is NOT a "separately derived system" and therefore: "Ground rods (grounding electrodes) are only required if the generator is a separately derived system." which means it doesn't need it.

    So why does Coleman and folks who appear to know something about generator safety claim such generators do? I guess to play it safe I could at least use a SINGLE 4ft ground rod. Some grounding would be better than none I suppose?
    Last edited by Cubey; 11-10-2007 at 10:11 AM.

  5. #5

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    Quote Originally Posted by Cubey View Post
    So why does Coleman and folks who appear to know something about generator safety claim such generators do? I guess to play it safe I could at least use a SINGLE 4ft ground rod. Some grounding would be better than none I suppose?
    Why do they say to do it? Simply put, to reduce lawsuits.

    The two examples you show here do not show there was a shock hazard because the generator not being attached to a ground electrode. There was a problem with the generators themselves. Possibly defective GFIs, wiring of the generator or camper, or other faults in the units themselves. The fact that someone using "an ungrounded generator" caused a shock to someone is merely anecdotal. Without any definite facts, it's difficult to comment. Does it mean there was no ground rod driven, or does it mean the generator's internal ground was not present?
    How many campsites provide you with metal pipe that has 10 feet in direct contact with the ground, for the express purpose of grounding a generator? Do you ever see folks jumping out of their Holiday Rambler for the night, start a fire, set up the awning, and drive an 8' ground rod? And even if you do drive a ground rod, is it an acceptable ground to prevent shock? In the 2005 NEC, Article 250.4(A)(5) states, in part, "The earth shall not be considered as an effective ground-fault current path.".
    So even if you ground the generator, by Code, an electrode in the ground may not provide the protection you seek.

    If you feel so inclined, go ahead a drive a rod. But IMPO, it's unecessary. Youre time would be better spent checking and maintaining the generator.
    Just my 2 worth.

  6. #6
    DIY Member Cubey's Avatar
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    Quote Originally Posted by 480sparky View Post
    Why do they say to do it? Simply put, to reduce lawsuits.
    That was my first thought about the notice to ground but the more I read and was told, the less I believed it.

    Do you ever see folks jumping out of their Holiday Rambler for the night, start a fire, set up the awning, and drive an 8' ground rod?
    *LOL* I couldn't help but laugh at that.

    But in all seriousness, generators which are built into RVs may be a completely different animal from portable generators since they are built for a permanent installation where there is always the same condition for grounding though I guess the same could be said for a portable generator.

    If you feel so inclined, go ahead a drive a rod. But IMPO, it's unecessary. Youre time would be better spent checking and maintaining the generator.
    It seems to be a about a 50/50 divided issue. Some people who use portable generators for RVing insist it is required for safety and have witnessed deaths from people not grounding when the manual tells you to, while others say they have been using generators for a long time and have ever had a problem.

    Is using a plug-in outlet tester a good way to quickly check proper electrical operation of a generator?

    The single outlet in my trailer was wired backwards (or some such issue) according to my plug-in tester. I unplugged the trailer, reversed the connections, plugged the trailer back in and plugged the tester back in and now it shows "Correct". Unsure about the light fixtures but I guess they may be less important than outlets. I added in some extra outlets and they all test out fine as well as the outlet I'm plugging the trailer into. So basically the wiring in the trailer for outlets should be correct now. Perhaps other RVs are wired incorrectly as well which could cause a problem when used with a generator.

  7. #7
    DIY Member Cubey's Avatar
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    I wonder if the risk lies in the RV wiring on older units. I found this on an RV forum with a long debate about portable generator grounding:

    There maybe some old RVs out there that have there neutrals bonded to ground from the factory but that has been against code for 20+ years. This is not a gray area, the code is real specific on that one. RVs are just like sub panels on a house, the ground and neutral are on separate buses. Now their is some debate on permanently installed generators but everyone I have seen has the neutral and ground bonded.
    Could that be the risk involved in running a generator without a ground rod, having an RV with neutral & ground bonded? My trailer is 40 years old so perhaps it has them bonded which is now against NEC code.

    --
    EDIT:

    I have visually inspected the breaker box in the trailer by removing the cover and the neutral/ground bonding screw is NOT present so it should be within current NEC code as far as that is concerned so that should not be an issue. Also, if it were, wouldn't that set off open ground, open neutral or something on the plug-in tester which shows "Correct" for everything?
    Last edited by Cubey; 11-10-2007 at 11:46 AM.

  8. #8
    In the Trades Bob NH's Avatar
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    A generator that has no reference to earth ground, as is the case if neither side of the winding is connected to earth, will not produce any voltage relative to earth ground on EITHER terminal. It is isolated and the effect is the same as grabbing the hot terminal of a battery; nothing happens.

    Because grounding one conductor of a generator causes the ungrounded conductor to have a potential relative to ground, it actually increases the hazard that can exist if one comes into contact with the ungrounded conductor.

    A GFCI doesn't rely on the existence of a ground. A GFCI measures the difference between the hot and the neutral currents and trips if they are not the same. There are many installations where GFCIs are installed BECAUSE no ground is available.

    In most cases a ground rod has too much resistance to trip a breaker even if there is a ground fault. The resistance would have to be 8 Ohms or less to trip a 15 Amp breaker at 120 Volts. It is common for ground rod resistance to exceed 25 Ohms.

  9. #9
    DIY Member Cubey's Avatar
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    What I am concerned about is if there is a failure of the GFCI outlet on the generator, will it sent hot current into the trailer's ground/chassis/aluminum skin? Seems like it might if the generator's neutral/ground is bonded. It would therefore bond the trailer's neutral and ground at the generator (I think?). I would not be able to exit the trailer without being shocked if that occurs unless I use something insulated to open the door and if someone touched the skin of the trailer they would be shocked. Also the propane tanks and pipes would be at risk of exploding. Scary thought!

    Perhaps I could use a secondary plug-in GFCI adapter between the generator and the trailer as extra insurance. One of these: http://www.altgarden.com/store/cart....t_detail&p=476 This way if the generator's GFCI fails, the extra one should work. If BOTH were to fail I guess it must just be my time to die since I would have done everything possible to be safe in terms of GFCI protection.

  10. #10
    DIY Senior Member BrianJohn's Avatar
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    Driving a rod/ground rod/electrode into the earth will serve NO PORPOSE. I defy anyone posting here to tell me what will be gained by this.

    In order for electrical grounding to be effective all metallic parts need to be bonded together.

    As for the RV guy knowing something about grounding GIVE ME A BREAK, he may know engines he may know generators, I can assure you he knows nothing about grounding.

  11. #11
    DIY Member Cubey's Avatar
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    Quote Originally Posted by BrianJohn View Post
    Driving a rod/ground rod/electrode into the earth will serve NO PORPOSE. I defy anyone posting here to tell me what will be gained by this.

    In order for electrical grounding to be effective all metallic parts need to be bonded together.

    As for the RV guy knowing something about grounding GIVE ME A BREAK, he may know engines he may know generators, I can assure you he knows nothing about grounding.
    Will using a plug-in GFCI adapter add a good backup in case the generator's GFCI fails? Plug the GFCI adapter into the generator and then plug in the extension cord for the trailer to the adapter. It would also be good for a backup GFCI at campgrounds/RV parks in case their GFCI fails. $20 seems like cheap insurance to ensure working GFCI. It might be overkill but if it helps me sleep at night, I'll spend the $20 for it.

    My trailer is a 15A system (not 30A or 50A like most RVs) so a standard 120v GFCI adapter like I posted above will work without using 30A cheater adapters or overloading the adapter.

  12. #12
    Electrical Contractor/Instructor jwelectric's Avatar
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    250.4 General Requirements for Grounding and Bonding.
    The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.
    (A) Grounded Systems.
    (1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

    The rod will do nothing unless the generator is struck be lightning

  13. #13
    DIY Senior Member BrianJohn's Avatar
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    Exactly and if you feel the need to ground the generator due to possible lightning strikes (which is possible) you should drive a electrode everytime you park it.

    If you have a proper GFCI and all metallic parts are bonded you are/should be safe. I say should because I have not seen/inspected your RV and do not know for a fact the wiring is safe.

  14. #14
    DIY Member Cubey's Avatar
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    Quote Originally Posted by BrianJohn View Post
    Exactly and if you feel the need to ground the generator due to possible lightning strikes (which is possible) you should drive a electrode everytime you park it.

    If you have a proper GFCI and all metallic parts are bonded you are/should be safe. I say should because I have not seen/inspected your RV and do not know for a fact the wiring is safe.
    Well, I did check the breaker box. The cover has a label and points out the neutral bonding screw location on the neutral strip and that hole is empty meaning the neutral/ground bonding screw isn't present, so the chassis/ground of the trailer is not bonded to the neutral so it should be "safe" and up to current NEC code as far as that is concerned.

    I think I will probably invest in the $20 plug-in GFCI to be extra safe with the generator as well as campground and RV parks that may have questionable GFCI on the electrical hookups.

    Typically lightning comes within thunderstorms that contain rain. Since I won't be running the generator exposed to rain, risk of lightning will be pretty much non-existent. If a storm is brewing off in the distance, I'd shut down the generator, move it up near the trailer and let it cool off as long as possible before the rain starts so I can cover it with a tarp just as the rain begins. I really have very small electrical needs and can actually get by without any electricity if need be in extreme situations if I have to short of very high temperatures since all I would be lacking is air conditioning/fans.

    The RV fridge is old so it is all mechanical, not 12v/computer controlled like new ones, the range is also 12v-less, the sink is pressurized (no electric pump), there is a single LP wall lantern which provides light and heat, I have a catalytic heater so I don't have a furnace requiring electric to operate. The generator is mostly for the air conditioner, the microwave and the converter which charges the battery and powers the 12v system.

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    DIY Senior Member BrianJohn's Avatar
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    I did not re-read the complete post, but if the RV panel has a neutral that is not bonded to ground, you need to utilize a 3-wire cable for 120 VAC (one hot/energized, one neutral one grounding conductor) or a 4-wire cord for 240/120 VAC (2-hots/energized, one neutral and one grounding conductor). This all assumes the neutral is properly bonded to the generator frame.

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