The arithmetic that explains everything
The names are misleading because they describe amps on a single leg, and the two services do not have the same number of legs.
30 amp service is a single 120V leg at 30 amps. 120 x 30 = 3,600 watts.
50 amp service is two 120V legs, each at 50 amps. 120 x 50 x 2 = 12,000 watts.
So 50 amp is not 67% more than 30 amp. It is roughly 3.3 times the available power, which is why coaches with two air conditioners are all 50 amp and coaches with one are mostly 30.
| 30 amp | 50 amp |
|---|
| Available power | 3,600 W | 12,000 W |
|---|
| Legs | One 120V leg | Two 120V legs |
|---|
| Connector | TT-30, three prongs | NEMA 14-50, four prongs |
|---|
| Typical coach | Travel trailer, small Class C, one roof unit | Fifth wheel, Class A, two or three roof units |
|---|
| Generator to match | 3,500-3,700 running watts | 7,500-12,000 running watts |
|---|
The connectors are not variants of each other
A TT-30 plug has three prongs: one hot, one neutral, one ground. A NEMA 14-50 has four: two hots, one neutral, one ground.
That difference is physical and electrical, and it is why adapters go only one way usefully. A 50 amp coach on a 30 amp pedestal, through a dogbone adapter, gets 3,600 watts — both legs of the coach are fed from the single available leg. Nothing is broken; you simply have a quarter of the power and have to manage loads accordingly.
Going the other way — a 30 amp coach on a 50 amp pedestal — is straightforward, and the coach still only draws its own 30 amps. That adapter is the useful one to carry.
The one genuine trap: a TT-30 looks superficially like a household dryer or RV-style outlet to people who have not met one before. It is 120V, not 240V, and plugging a coach into the wrong thing is an expensive mistake.
What 30 amps actually runs
3,600 watts sounds generous until an air conditioner joins the list.
| Load | Running watts | Share of 3,600 W |
|---|
| 13,500 BTU roof air conditioner | 1,200-1,700 W | Up to about half |
|---|
| Microwave | 1,400-1,600 W at the wall | Another 40% |
|---|
| Water heater on electric | 1,400 W | Another 40% |
|---|
| Converter charging the house battery | 200-600 W | Modest but continuous |
|---|
| Refrigerator on electric | 150-400 W | Small |
|---|
| Lighting and devices | Under 200 W | Negligible |
|---|
RV appliance figures are typical published ranges; microwave draw is input rather than cooking power, which the microwave page explains.
Add the top three rows and you are past 3,600 watts. That is the daily reality of a 30 amp coach: the air conditioner and the microwave are an either-or, and the water heater goes on propane.
Managing 30 amps well
- Put the water heater and fridge on propane. Both appliances usually offer it, and both are large electric loads for no benefit.
- Treat the microwave as a pause. Air conditioner off, microwave on, microwave off, air conditioner back.
- Fit a soft starter if the compressor start is what trips you rather than the running total.
- Watch the pedestal voltage. Older parks sag badly on hot afternoons, and low voltage damages compressors — a monitor with fault diagnostics is worth carrying.
Matching a generator to the service
The principle is the same one that governs house backup: the connection caps the machine, so size them together.
For 30 amp, a 3,500-3,700W inverter generator with a TT-30R is the natural match. Going bigger buys nothing the cord can pass.
For 50 amp, you need a machine with a 14-50R to use both legs. A 7,500W machine covers most real 50 amp coaches; only a very demanding one approaches the full 12,000W.
The RV generator roundup covers the machines, and the RV power station page covers the battery side, which is the better answer for everything except air conditioning.
The short version
- 30 amp is 3,600W. 50 amp is 12,000W. Two legs, not one.
- TT-30 has three prongs; 14-50 has four. Different connectors, not variants.
- A 50 amp coach on a 30 amp pedestal works — at a quarter of the power.
- Match the generator outlet to the service, then size the watts to that.
