If you read my last post, we began a discussion about grounding and bonding of portable generators. To begin, we talked about a standard residential electrical service and specifically discussed the ground wire system, the neutral wire system, and the single bonding point between the two systems. Lastly and most importantly, we also described what we referred to as a sub-panel and how important this is to us as RVers.
So, here we go with the next point: the breaker panel in your RV is a SUB-PANEL. When you pull into the campground and plug in your shore power, you are becoming a sub-panel to the main panel which is permanently installed at the campground. Therefore, the neutral wiring system and the ground wiring system in your motorhome are not bonded together. All the ground wires terminate in a ground bar within the breaker panel, and all the neutral wires terminate at a seperate bar within the breaker panel. The neutral and ground systems are kept isolated from each other. The bonding or connecting together of the two wiring systems is taken care of in the campground wiring system not in the RV.
Keeping in mind that the above discussion dealt only with the power supplied by the shore power cord, the next step is to look at what happens if your RV has an on board generator set, particularly with an automatic transfer switch. With an on-board generator we are faced with a problem because the breaker panel in the RV has an isolated neutral bar and ground bar, yet proper wiring calls for a single bonding point SOMEWHERE! Thus, the neutral and ground wiring systems coming from the on-board generator is bonded at the generator. This point is important for safety, but it is also important when you consider a portable generator powering an RV.
When you look at most portable generators, you will find that the generator has what is known as a “floating neutral”. What this means is that the neutral from the generator, and the ground from the generator are NOT bonded together at the generator! Why is this? Consider that many portable generators are sold to home owners who are going to use the generator as an emergency power source for their home. When you realize that the generator will probably be connected to the home’s main breaker panel, and remembering that panel is already bonded by code, it would be a code violation for the generator to also be bonded. So, generator manufacturers do not bond the neutral and ground systems. However, when one of these generators is connected to an RV, it is connected to a breaker panel that is NOT bonded. Since the generator and the breaker panel is not bonded, we have a code violation and a safety issue.
There are several ways to address this problem, depending on the generator and we will talk about these methods next post. Until then,
Happy RVing
Larry