RV Electrical Basics For First-Time Owners

The two systems

Two consequences fall straight out of that table. If your lights work but the air conditioner does not, you have a 120 V problem — shore power, breaker, or the pedestal. If your air conditioner works but the lights are dim, you have a 12 V problem — battery, or the converter not charging it.

Converter: the box that turns 120 V shore power into 12 V to run the 12 V system and charge the battery. Not to be confused with an inverter, which does the opposite — 12 V battery to 120 V, for running outlets without shore power.

Shore power: the 30 or 50 amp question

Look at the plug on your cord. Three prongs with one angled is 30 amp, a single 120 V circuit of about 3,600 watts. Four prongs is 50 amp, two 120 V legs of about 12,000 watts total.

On 30 amp you are managing a budget. The air conditioner takes 12–16 amps running, the microwave 10–13, the electric water heater 10–12. Two of those at once is usually fine; three trips the breaker. The two services compared.

And the pedestal is not to be trusted. Buy an EMS before you buy anything else electrical — low voltage in a full park is the fault that actually damages equipment. Surge protector vs EMS.

The battery, and why it is flat

Your trailer’s battery runs the 12 V system. It charges from shore power via the converter, from the tow vehicle while driving (slowly), and from solar if fitted.

Three things drain it faster than people expect. The propane and CO detectors run continuously — they have to. The furnace blower is a surprisingly heavy 12 V load, so a cold night off grid takes a real bite. And the refrigerator control board draws constantly even when the fridge is running on propane.

Which is why a trailer left in storage with the battery connected is flat in a few weeks. Use the battery disconnect switch if yours has one, or disconnect a terminal.

Breakers and fuses: two panels, not one

Open your trailer’s electrical panel and you will usually see both systems in one cabinet.

Breakers — the switches — protect the 120 V circuits. One main, then branch breakers for the air conditioner, outlets, water heater and converter. These reset.

Fuses — usually blade fuses in a row — protect the 12 V circuits. These do not reset; you replace them, and you carry spares in the sizes your panel uses.

A tripped breaker trips for a reason. Resetting it once is diagnosis; resetting it repeatedly without finding out why is how a problem becomes a fire.

The GFCI nobody tests

One of your trailer’s outlets — usually in the bathroom — is a GFCI, and it protects several other outlets downstream of it. When it trips, several outlets stop working at once and people conclude the trailer has a serious fault.

Press the reset button on that outlet. It solves “half my outlets stopped working” a remarkable proportion of the time.

And test it occasionally with the test button, or with a receptacle tester that has a GFCI test. A GFCI that will not trip when tested is a GFCI that will not protect you, and that is worth knowing before you need it.

The five things to do first

1. Find out whether you are 30 or 50 amp and buy the matching protector.
2. Buy an EMS, not a surge protector, and lock it to the pedestal.
3. Buy the 50-to-30 dogbone adapter — the one you will use most — and the 30-to-15 for home.
4. Learn your 30 amp budget. Which two appliances you can run together and which three you cannot.
5. Find the battery disconnect and the GFCI outlet. Both will save you an unnecessary service visit.