Generator bonding and grounding
In previous posts we have discussed what is meant by “bonding” in an electrical distribution system. This is an important concept. If it seems like I am dwelling on this, I want to make sure we are clear on what bonding means.
The ground wire system and the neutral wire system are two separate wire systems. By code, they are to be connected together at ONE point and only one point. If there is more than one bonding point in the wiring system, you can create ground faults, circulating currents and possibly prevent a breaker from tripping if there is a short circuit. If there is no bond, it is also possible that a breaker will not trip.
The breaker panel in your RV is classified as a sub-panel. As such there is NO bond in the panel and the neutral/ground wiring systems in your RV are NOT connected to each other anywhere in the RV. This is because when you plug in your shore power cord, you become part of the campground electrical system which IS bonded, again, at ONE point in the entire campground, generally at the campground main breaker panel.
If you have a generator that is permanently installed in your RV, such as is typical in Class A motorhomes, the generator has a bond between the neutral and the ground, such that when the transfer switch switches, the isolated neutral and ground systems get connected together.
If, however, you use a portable generator, sitting on the ground or in the back of your pickup truck, a problem occurs. Typically portable generators are made with isolated grounds and neutrals, meaning the ground and the neutral are not bonded in the generator. Since the ground and the neutral are also not bonded in the RV, this creates a code violation and a possible safety hazard which needs to be corrected.
This problem cannot be corrected by driving a ground rod into the dirt, and connecting it to the generator, and it cannot be corrected by connecting the generator case to the motorhome frame. Neither of these procedures connects the neutral to the ground. The only way this can be accomplished is to properly connect the neutral wire to the ground wire with a properly sized and properly connected bond wire installed at the proper location in the electrical system.
When considering solutions to this problem, it is probably not a good idea to consider installing a bonding wire in the breaker panel. Remember, when you unplug the generator and plug into a shore power outlet, the shore power outlet will provide a proper bond and if you have another bond in your breaker panel, you have a new code violation.
The best place to create a neutral/ground bond is at the generator itself.
By doing the bonding at the generator, you preserve the ground/neutral isolation within the RV electrical system. I have been reading instruction manuals for various manufacturers generators and have concluded that they are not too clear on this whole subject. So far I have not seen any of the manuals that even address the subject of neutral/ground bonding. About the only subject that is mentioned is the actual grounding of the generator case which is a whole other subject not connected (no pun intended) to this subject.
Since the manufacturers seem to ignore this subject we are left on our own to solve the problem. If I had a portable generator to be used to power my RV, the first thing I would do, if there was no procedure described in the manual, would be to contact the manufacturer and ask them what they would recommend, and then ask them for the recommendation in writing. Remember we are talking about a potential safety hazard here. The reason I recommend getting it in writing is because we don’t want to have any potential warranty issues.
Of course there is the strong possibility that the manufacturer will not provide a recommended bonding procedure which leaves you on your own to make one up. Assuming you are using the portable generator to power your RV ONLY, and if it were my generator, I would take the case apart and install a permanent jumper between the ground and the neutral wires inside the case. The reason I say this is because if you also plan to use the generator as an emergency power source for your home, the bond wire will need to be removed in order to be in code compliance.
For a 30 amp generator, the bonding wire should be at least a #10 wire. For a 50 amp, 240/120 volt generator, the bonding wire should be at least a #6. I can’t give you specific installation instructions because every generator is different. If you are comfortable doing electrical work, follow the basic suggestions above. If you are not comfortable, I would suggest contacting a generator repair shop to have it done. Keep in mind that this is a subject that creates a great deal of confusion and there is no guarantee that the shop you chose will even understand what you are asking. If they shop you talk to seems confused about your request, search out another shop until you talk with someone who sounds comfortable with your request.
Finally for this post anyway, I would suggest you verify that the modification is done properly. In our next post, we will discuss how you should do this test. Until then,