Utility Terms

Black Tank. The Black Water Tank is the holding tank in the bowels of a motorhome, 5er, or travel trailer (no pun intended) that stores human waste from the toilet.

Gray Tank. The Gray Water Tank is the holding tank in a motorhome, 5er, or travel trailer that stores waste water from the kitchen sink, the tub and/or shower, and the lavatory sink.

City Water. The water source to the RV when it is connected via a hose to a water spigot external to the motorhome (the usual situation when you are in a campground with electric and water hookups).

Shore Power. The electrical power source when an RV is connected via an electrical cable to a source of electrical power external to the motorhome (the usual situation when you are in a campground with electric and water hookups).

Generator Power. This term should be self explanatory—when the motorhome is getting electrical power from a generator (usually self-contained) rather than being plugged into an external utility power receptacle.

Battery Power. This term should also be self-explanatory. This is the usual state when you are not connected to an electrical source, but you using the lights or other 12-volt items in your RV. The radio and some smaller TVs can run directly off of 12 volts.

There are two separate sets of batteries in motorhomes—one or two for the engine, and two, three, or four batteries for the living spaces of the RV.

Chassis Battery. The chassis battery (sometimes referred to as the engine battery) is just like the one in your car or truck, that starts the engine and is charged from the alternator attached to the engine. Gasoline coaches usually have only one chassis battery, while most diesel coaches have two chassis batteries (needed to start the bigger, much higher-compression engines).

House Batteries. The house batteries are separate RV/Marine deep cycle batteries that are used to power the living spaces in your RV and are especially designed to handle the repeated cycles of deep discharges and then being recharged. The house batteries power all or most of the lights and 12-volt items in your RV, such as ceiling fans, radios, and small TVs, and, yes, even the furnace (which can quickly draw down your batteries).

The house batteries are charged from the engine’s alternator while it is running and charged from your converter when you are connected to an electrical power source.

Converter. A converter is an electronic device that converts 120 volt AC (alternating current) electricity (from the RV shore power cable) to 12 volt DC (direct current) power for powering the 12 volt lights and other small items in your RV, while at the same time charging up the house batteries. Most converters also include a battery charger, so that your house batteries are being charged while you are plugged into electrical power or when you are running your generator.

Inverter. An inverter is an electronic device that takes 12 volt DC from your house batteries and converts it to 120 volts AC to run most of your appliances and electronic items. An inverter allows you to use your regular electrical appliances even when you are not connected to an electrical power source. Some RVs can be fitted with a small inverter to power the front TV, the VCR, and even a satellite receiver. Larger inverters can be used to power the microwave, a curling iron, and other high wattage devices.

Except on the more expensive coaches, an inverter is an optional, extra charge item. But please be aware that you need at least four house batteries to run the larger inverters for the microwave.

Generator. Most of you already know what a generator is—an internal combustion engine connected to a device (a generator) that produces 120 volt alternating current electricity (the same type of electricity that you have at home). Generators are powered by gasoline engines, LP (propane) engines, or diesel engines. Generators can be built into a motorhome, as most are, or they can be free-standing units used by many trailer or 5th wheel owners. Generators come in many different sizes and are rated by the amount of power that they can produce.

Most generators only produce 120 volt AC power, but some of the larger units can produce both 120 volt and 240 volt AC power.

On most coaches, generators are an optional, extra cost item.

Transfer Switch. A transfer switch is now standard on all newer motorhomes, but is not always found on older motorhomes. A transfer switch is connected to both the shore power cable and to the generator and is used to ensure that only one source of AC power is feeding your coach. (Dire consequences can happen if your shore power and generator connections ever get together at the same time.)

A transfer switch allows you to use either source of electrical power without doing anything to change from one to the other. On older coaches without a transfer switch, you had to go outside and plug your shore power cable into the generator to get generator power into the coach.

[Enough talk about electrical terms for now. Solar power, inverters, charge controllers, and battery charging can easily consume an entire seminar.]

I have tried to only acquaint you with the terms that are most commonly used.