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Like real estate, location is important. If at all possible, don't install an inverter in the battery compartment. Battery gasses are corrosive and can cause damage to an inverter's circuitry. At the same time, a delicate balance is called for — the cables running from the inverter to the battery bank must be as short as possible. Long cable runs, or too small a cable — these are at the root of many inverter problems, and can create safety issues as well. ALWAYS follow the specifications provided by the inverter manufacturer when installing cable runs.
When wiring up the power leads, double check battery polarity to inverter connections--reversed polarity usually spells instant inverter demolition. And when you connect your battery terminals, be ready for a spark, particularly with larger inverters. The "pop!" and light flash can be a bit surprising and disconcerting if you're not ready for it. Even with the inverter power switch in the "off" position, most inverters have large capacitors ahead of the power switch.
What do you do with the shore power from the inverter? We're assuming that you're installing a large inverter, capable of powering most "house" loads. As a result, the inverter will be close to the batteries, and out of handy reach for directly plugging in an appliance or accessory. This means you'll want to route the inverter output into your rig's shore power circuitry. The simplest way to do this is to plug the RV shore power cord directly into the inverter. Here's how.
In most cases, that's not real practical, since the inverter will not likely be near the shore power compartment. Many RVers run suitably sized shore power wires ("Romex" and the like) from the compartment where the inverter is located out to the shore power cord storage compartment. On the inverter end of the wiring, install an electric plug that will mate up to the inverter. At the other end, mount a shore power receptacle in a steel work box, running the romex to this receptacle. It's best to firmly mount the work box to the RV. Equipped with a 30 amp, 120 volt receptacle, this is where you'll "plug in" your shore power cable. IF your rig has a 50 amp plug, you'll need to use a suitable adapter to mate up.
By running the inverter output to a receptacle, you'll always be forced to "plug in" the RV shore power plug--thus preventing you from accidentally turning on the inverter while the RV is plugged into utility based power--a disaster if ever there was. As an alternative, an electric "transfer switch" as might be used with a home-based generator system can be used to prevent these problems; it's easier to deal with than having to physically plug in the shore power cord, but is more expensive and complex as an install.
We found it best to put a switch in the 120-volt side of our RV's power converter. Why? Because when our power inverter is turned on, we don't want the power converter chewing up our "home brew" shore power. And if your RV refrigerator automatically rolls off LP and onto shore power, you'll want to disconnect the refrigerator shore power cord when boondocking.
Once again, if you're not comfortable or SURE about what you're doing when working with RV electrics, HIRE qualified help to do the installation.