I was attending the Gypsy Journal rally at Celina Ohio last week and while attending one of the seminars, the subject of grounding and/or bonding of portable generators came up, associated with a lot of confusion and mis-information on the subject. Let me say up front that I am not an expert on the subject, but before writing this post, I did bone up on the appropriate sections of the National Electrical Code and in that exercise, I learned a little about the subject.
As always when I discuss a subject, I like to have a vocabulary in common with others. On this subject, there are two words we have to agree on, and understand, they are “bonding” and “grounding”. These two words are frequently used together and sometimes even used interchangeably. That is not correct as the two words have two distinct meanings and I believe this leads to a lot of confusion on this issue.
First let’s use a common residential dwelling to begin our discussion. In a newly constructed home, electric code requires the incoming power to be grounded by means of at least one and many times, two ground rods driven into the earth. The ground wire from your breaker panel is connected to this/these ground rod(s) and then continues to run throughout the house with all the ground wires tied together.
In addition to the ground wire system in the house, there is another wiring system known as “neutral”. The neutral wire is generally white in color and similar to the ground wire, it runs to all electrical devices in the dwelling.
Now the important point: At one place, and only one place, the ground wire system and the neutral wire system are tied together. This is know as the bonding point and typically occurs in the breaker panel. Think of this in terms of roadways. You have two roads running side-by-side, but not intersecting, except at one point where there is a connecting street.
Now another consideration: if you add a second breaker panel in your house, that is fed from the first panel, there are special considerations. The most important one is that the grounds and the neutrals cannot be connected in the sub panel, and the ground bus bar is to be isolated. This is to prevent a second bonding point from occuring in the sub-panel, keeping in mind that there is to be one, and only one, ground/neutral bonding point.
Ok, now let’s summarize: from the utility company pole out at the street, you have a total of three wires coming to your house: you have two hot wires, and a neutral wire. All three of those wires enter your house and run through the breaker panel to your outlets and switches and appliances. At a point near the breaker panel there is a ground rod with a wire connected to it. This ground wire also runs through the breaker panel and to the various electrical devices. The ground wire and the neutral wire are only connected together in the main breaker panel, and not in any sub-panels.
Think about all this information and we will see in the next post how it affects the breaker panel in your RV, and how this affects a portable generator connected to your RV.