30 amp vs 50 amp RV: the watt math

The short version

Why 50 amp is more than 20 amps more

It is natural to read “50” as about two-thirds more than “30.” But a 50 amp service is two separate 50 A circuits at 120 V, one on each leg of the 120/240 V supply. Each leg alone carries 6,000 W — more than a whole 30 amp rig — and together they carry 12,000 W, more than three times as much. That is why big fifth-wheels and diesel pushers with two or three air conditioners, residential fridges and washer-dryers come with 50 amp service.

30 A RV: 120 V × 30 A = 3,600 W
50 A RV: (120 V × 50 A) + (120 V × 50 A) = 12,000 W

What fits in 3,600 watts

Add the top of those ranges and it is clear why 30 amp owners learn to juggle: the air conditioner, fridge and microwave together can approach 3,600 W, and adding the electric water heater or a hair dryer trips the breaker. Running the water heater on propane and not using the microwave while the AC is running are the usual habits.

Generators for each

A 30 amp rig with one air conditioner needs a generator in the 3,500 W class; without the AC, about 2,000 W. A 50 amp rig running two air conditioners needs something like 8,000 W running and more to start them. The detailed sums are on what size generator for a 30 amp camper and what size generator for a 50 amp RV with 2 AC units. Fuel for a weekend is on how long a generator runs on 5 gallons of gas.

One catch: a 14-50R outlet on a generator doesn’t guarantee 50 A on each leg. Champion’s 8500 W inverter, for example, labels its 14-50R as 120/240 V 29.2 A — the generator’s rating, not the plug shape, decides how much it can supply.

Adapters (“dogbones”)

• 50 amp rig, 30 amp pedestal: an adapter lets you plug in, but you only get 3,600 W in total — the rig’s two legs share one 30 A, 120 V supply. Manage loads as if you had a 30 amp rig.
• 30 amp rig, 50 amp pedestal: an adapter connects one leg of the 50 A outlet to your rig. You still have a 30 A main breaker, so still 3,600 W.
• 15/20 amp household outlet: enough to keep the batteries charged and run lights and the fridge; not an air conditioner on a typical household circuit.

Use a surge protector between the pedestal (or generator) and the rig either way. Some also flag low voltage — common at busy campgrounds on hot afternoons — before it harms an air conditioner’s compressor.

Inverters in an RV: converter off, transfer switch on

• Turn the converter off when the inverter runs the RV. The converter — the RV’s built-in battery charger — runs on 120 V. If the inverter feeds the same outlets, the converter would charge the battery from the battery, wasting energy in a loop.
• Use a transfer switch or an inverter-charger to switch the RV’s 120 V circuits between shore power, generator and inverter. An inverter-charger can replace the converter altogether. Have it installed by a qualified RV technician or electrician.
• 30 or 50 amp makes no difference to the inverter. What matters is its continuous and surge rating and the battery behind it — see what size inverter to run a microwave.

Running on solar and batteries instead

Off-grid, 30 vs 50 amp hardly matters: the limit is your battery bank and inverter. A 2,000–3,000 W inverter runs most RV loads except air conditioning for any length of time. How much solar for an RV sizes a boondocking system around a 2 kWh day, and what size inverter to run a microwave covers the inverter.