I would like to spend a bit of time discussing switches, particularly as they are used in motorhomes, and more specifically the notorious transfer switch. There are several different kinds of transfer switches but I would like to focus on what is normally called an automatic transfer switch. The word transfer refers to the action of the switch when it takes incoming power, either from a shore cable, or from a generator set, and directs that power into the RV, to the breaker panel.
While it sounds simple, this is actually a fairly complex process involving switching a lot of power, making certain that proper grounding and bonding of electrical wiring is taken care of, and doing so in a manner that is convenient and safe.
Consider this scenario: You have been traveling in your generator equipped RV and you arrive at the campground where you pull into your campsite, pull out your shore power cord, plug it into the power pole and then sit back to enjoy your campging adventure. Since you are lucky enough to have an Onan quiet diesel generator in your RV, in your rush to relax, you have left your generator running, and yet, your RV is now running on the power being supplied through the shore power cable and the power being produced by the generator is being ignored.
This is because you “intelligent” automatic transfer switch has made a decision to select the shore power in preference to the generator power. This selection is by design, and is logical and appropriate. In addition, the shore power is isolated from the generator power for safety so that none of the shore power is present at the generator and none of the generator power is present at the shore power cable. This is obviously for safety reasons. Another safety feature that happens during this changover is that proper grounding is applied. When you are plugged into shore power, the grounding for your RV is supplied by the shore cable and comes from the power pole at the campground. When you are running on your generator, the grounding is supplied by the connection to the generator.
We will talk more about transfer switches in the next post, including contact rating, and how to preserve the life of your transfer switch.