Generator cord 30 amp vs 50 amp: which do you need?

Generator cords come in a few plug styles, and they are not interchangeable. The right one depends on the outlet on your generator and what you're plugging into: an RV, or a power inlet box that an electrician installed on your house.

The three plugs you'll see most

Plug	Volts	Amps	Max watts	Prongs	Common use
TT-30	120 V only	30 A	3,600 W	3 (hot, neutral, ground)	RVs and travel trailers
L14-30	120/240 V	30 A	7,200 W	4, twist-lock	Home backup inlets and transfer switches
14-50	120/240 V	50 A	12,000 W	4, straight blades	50 amp RVs, larger home inlets

Max watts = amps × volts. For the 240 V plugs, that's the total across two 120 V "legs."

• TT-30: 30 A × 120 V = 3,600 W. It's a 120 V plug, even though it looks a bit like a 240 V one.
• L14-30: 30 A × 240 V = 7,200 W, or 3,600 W on each leg.
• 14-50: 50 A × 240 V = 12,000 W, or 6,000 W on each leg.

Those are ceilings, not targets. For loads that run for hours, plan on staying below about 80% of the rating. Wikipedia's NEMA article, for example, notes that a 30 A 14-30 plug is limited to 24 A continuous.

30 amp or 50 amp: which do you need?

For an RV, match the RV's plug.

• A 30 amp RV has a TT-30 plug. It's 120 V only.
• A 50 amp RV has a 14-50 plug. It's 120/240 V.

For a house, match the power inlet box your electrician installed.

• A 30 amp inlet usually takes an L14-30 cord.
• A 50 amp inlet often uses a different twist-lock plug on the house end. One maker's 50 A cord, for example, goes from a 14-50 plug to an SS2-50 connector. Check your inlet before you buy.

Your generator decides the ceiling. A generator with only a TT-30 outlet can't feed a 240 V well pump, whatever cord you use. Some larger generators have both an L14-30 and a 14-50 outlet.

Can you use a 30 to 50 amp adapter?

Adapters exist, but an adapter doesn't add power. If you plug a 50 amp RV into a 30 amp generator outlet, you get at most what the 30 amp outlet gives: 3,600 W on a TT-30. Run fewer things at once.

Never use any cord or adapter with a plug on both ends to feed a house outlet. That's a backfeed "suicide cord," and it can kill a utility worker or you. See interlock kits vs transfer switches for the safe ways.

How much power will you actually use?

Amps = watts ÷ volts

Use the calculator above to add up what you want to run. It's pre-filled with a fridge, a ½ HP sump pump, a furnace fan and lights, about 2,200 running watts.

Worked example

That 2,200 W, all at 120 V, is 2,200 ÷ 120 = about 18 A. Even if it all lands on one leg, it fits under a 30 A cord's 24 A continuous limit.

Add a 1,000 W, 240 V well pump. That's 1,000 ÷ 240 = about 4 A on each leg. Now you need a 240 V cord, like an L14-30. A TT-30 can't carry it at all.

If your total running watts climb past about 5,800 W (80% of 7,200 W), step up to a 50 amp setup.

What wire gauge should the cord be?

Lower gauge numbers mean thicker wire. Thicker wire carries more current and wastes less power.

Cord	Typical wire	What the numbers mean
30 A (TT-30 or L14-30)	10 AWG	10-gauge; "10/3" means three wires, "10/4" four
50 A (14-50)	6 AWG	"6/3 + 8/1" means three 6-gauge wires plus one 8-gauge

Makers' own 30 A generator cords list 10-gauge wire, and a 50 A RV cord lists 6/3 + 8/1 AWG. The ampacity table in Wikipedia's wire gauge article gives 10 AWG 30 A and 6 AWG 55 A in its lowest temperature column.

Read the jacket. The amp rating and wire size are printed on it. Don't use a cord rated below the outlet it plugs into.

Does cord length matter?

Yes. Longer cords lose more voltage. A little loss is fine, but a lot makes motors run hot.

Voltage drop ≈ 2 × length (ft) × amps × ohms per 1,000 ft ÷ 1,000

Copper wire resistance: 10 AWG is about 1.0 ohm per 1,000 ft, and 6 AWG about 0.40.

Cord at full load	25 ft	50 ft	100 ft
30 A on 10 AWG	1.5 V (1.2%)	3.0 V (2.5%)	6.0 V (5.0%)
50 A on 6 AWG	1.0 V (0.8%)	2.0 V (1.6%)	4.0 V (3.3%)

Percentages are of 120 V. At lighter loads, the drop shrinks in step.

The takeaway: use the shortest cord that keeps the generator at least 20 feet from your home. For most homes that means 25 to 50 feet. If you need 100 feet, a thicker cord helps.

Cord safety basics

• Inspect it every time. OSHA says never use frayed or damaged cords, and to make sure they're rated for the load.
• Keep all three (or four) prongs. NFPA says to check the grounding pin is there.
• Keep connections dry. Don't run cords or plugs through standing water.

Plugging your generator in with a good cord doesn't make it safe to move closer. It must stay outdoors, 20+ feet from the house, with the exhaust pointed away. Read our generator carbon monoxide safety guide.