Generator outlets look similar but are not interchangeable. Here is how to tell 5-20, TT-30, L14-30, and 14-50 apart, and how to match a cord to your generator.
The 30-second answer: Generator outlet types come down to a few common receptacles: the household 5-20R (120V, 20A), the RV TT-30R (120V, 30A), the twist-lock L5-30R (120V, 30A), the four-prong L14-30R (120/240V, 30A), and the 14-50R (120/240V, 50A). Match your cord’s plug shape and amp rating to the outlet, and never use a cord with a male plug on both ends.
The short version
- The number after the dash is the amp rating. Voltage and prong layout tell you what it’s for.
- A 30-amp 120-volt outlet delivers about 3,600 watts. A 30-amp 120/240-volt outlet can deliver up to about 7,200 watts across both legs.
- Cords and adapters must match both the plug shape and the amp rating, or they overheat.
- A cord with a male plug on both ends can energize live prongs and backfeed your house. Never make or use one.
What Do the Outlet Names on a Generator Mean?
Those letters and numbers come from NEMA, the standards group that defines plug and receptacle shapes in North America. Take “L14-30R” as an example. The L means twist-lock, the 14 is a configuration number that tells you it’s a 120/240-volt, four-wire layout, the 30 is the amp rating, and the R means receptacle, the female side on the generator. The matching plug on the cord ends in P. Once you can read that code, you can look at any outlet on a generator and know what it’s built to do. I’ve stood in more than a few driveways helping people figure out why a cord that “looks right” wouldn’t fit, and nine times out of ten it’s one digit in this code that doesn’t match.
The Common Generator Outlet Types
| Outlet | Voltage and amps | Max power | Typical use |
|---|---|---|---|
| 5-15R / 5-20R duplex | 120V, 15 or 20A | 1,800 to 2,400 W per outlet | Household cords, tools, lights, chargers |
| TT-30R | 120V, 30A | About 3,600 W | RV hookups |
| L5-30R | 120V, 30A, twist-lock | About 3,600 W | Larger portables, locking connection |
| L14-30R | 120/240V, 30A, four-prong twist-lock | About 7,200 W at 240V | Transfer switches, 240V equipment |
| 14-50R | 120/240V, 50A, four-prong | Up to about 12,000 W at 240V | Large generators, big RVs, welders |
Those wattage figures are the outlet’s maximum. The generator’s own rating is the real limit, so a 3,500-watt generator with a 30-amp outlet still only makes 3,500 watts. I always tell people to size by the generator, not the plug, and it’s easy to buy a 50-amp cord for a generator that can’t feed it.
The Household Outlets: 5-15R and 5-20R
These are the standard duplex outlets for everyday cords. Many generators use a 5-20R, which has a T-shaped slot on one side so it accepts both 15-amp and 20-amp plugs. Most come with GFCI protection built in or on the panel. If one is dead, check the GFCI reset button first, then the breaker (GFCI outlet not working). If the breaker keeps tripping, see generator keeps tripping breaker.
The RV Outlet: TT-30R
The TT-30R is the 30-amp RV receptacle with three angled blades. It’s 120 volts only. You’ll find it on many mid-size portables and inverter generators intended for campers. Most RV power cords use this plug, so it connects directly. If you plug in a household adapter, you’re limited to 15 or 20 amps at that adapter, which caps your power. That surprises a lot of people. A 30-amp RV running an air conditioner can pull more than a household cord can carry, so I always suggest running the RV cord straight into the TT-30.
The Twist-Lock 30-Amp Outlets: L5-30R and L14-30R
Twist-lock plugs rotate and lock in place so they can’t vibrate loose or get yanked out. That’s why bigger portables use them.
- L5-30R is 120-volt only, three-prong, 30 amps.
- L14-30R has four prongs: two hot legs, a neutral, and a ground. It supplies 240 volts across the two hots and 120 volts from each hot to neutral. It’s the outlet most people use to feed a home through a transfer switch (interlock kit vs. transfer switch).
Some generators have a selector that lets you choose 120-only or 120/240 output on the same outlet, so check the panel and the manual before you plug in.
The Big One: 14-50R
I treat anything at this amperage with respect. The 14-50R is a four-prong, 50-amp, 120/240-volt receptacle, similar to the one on an electric range or a large RV. You’ll see it on bigger portables, usually 7,500 watts and up. These need heavy cords with thick gauge copper, and they’re expensive. If you don’t have a specific reason to use one, it probably isn’t the right choice for you.
Cords and Adapters That Are Safe
Adapters are fine when you respect the amp limits. A few examples I use myself:
- A TT-30 to household adapter lets you run regular cords from an RV outlet. Each household cord is limited by its own rating, usually 15 amps (1,800 watts).
- A 14-50 to TT-30 adapter lets a big generator power an RV. The RV only draws up to 30 amps, even though the generator outlet can supply more.
- An L14-30 breakout cord splits one outlet into several 120-volt household outlets. Keep each leg under its amp rating and spread the loads between the two legs.
Heavy loads need heavy cords. If the cord feels warm, that’s a warning. See what size extension cord for a generator and cord overheating or melting.
Safety — quick reminders.
A cord with a male plug on both ends, meant to plug a generator into a wall outlet, makes the exposed prongs live when the generator runs. It can electrocute someone and backfeed power onto utility lines, endangering line workers. If you want to power your house, use a transfer switch or interlock kit installed by a qualified electrician. I won’t build one of these, I’ve never installed one, and I’d urge you not to either.
How to Pick From the Generator Outlet Types
- Look at the amp and voltage rating on the equipment you want to power. It’s printed on the label.
- Find the outlet on the generator that matches that plug shape and rating.
- Check that the generator’s total capacity covers the load (what size generator do I need).
- Use a cord rated for at least the equipment’s amps and the length you need.
- Plug in the biggest load first, then add smaller ones.
A tip from my years in the shop: when an outlet seems dead, don’t assume the outlet is bad. Check output at the generator with a meter before you start replacing parts (multimeter output test). Nine times out of ten, a tripped breaker or a reset button is the problem, not the receptacle.
Grounding and Safety Basics
Generators with a bonded neutral and a ground connection to the frame need proper grounding in some setups. The rules differ for portable use and for home connections, so read grounding a portable generator before you plug into anything permanent. And never run a generator in wet conditions without protection (run a generator in the rain).
Video walkthrough
Frequently Asked Questions
Can I plug an RV into a household outlet on a generator?
You can with an adapter, but you’ll be limited to about 15 or 20 amps. It’s usually better to use the TT-30 or a 14-50 to TT-30 adapter for full power.
What’s the difference between L14-30 and 14-30?
The L means twist-lock. A 14-30 (no L) is a straight-blade dryer-style plug. They’re not interchangeable, and it’s an easy mistake to make at a hardware store counter.
How many watts can a 30-amp outlet deliver?
At 120 volts, about 3,600 watts. At 240 volts across both legs, up to roughly 7,200 watts. The generator’s rating is the real limit.
Can I use a 20-amp cord on a 30-amp outlet?
With the right adapter, yes, but the cord limits the current to its own rating. I’d never use a cord with an amp rating below what the load needs.
Why does my generator have both 120 and 240 outlets?
Most home appliances use 120 volts, and large items like well pumps, dryers, and ranges use 240. Having both makes the generator more flexible. See generator for well pump sizing if you’re planning a pump.