Extension cord sizing for a 15 A pressure washer

Read the plate on your washer. Most consumer electric units land at 13–15 A on 120 V while the pump is running. That number is continuous-ish draw under spray, not the first instant the motor spins up. Start surge is uglier, same as an air compressor. A cord already sagging at nameplate sags more on that hit. Pressure falls, the motor heats, the outdoor GFCI trips, and people blame the washer.

Gas washers are a different product: they do not want an extension cord. Some larger electric units are 20 A or 240 V and want a dedicated receptacle, not a 15 A outdoor reel. This page is the 13–15 A, 120 V driveway load. Many manuals say use the shortest cord you can, or none. If the hose can reach from an outlet, let the hose travel.

Shop picks for a 15 A electric washer

Same copper planning math as the master chart — NEC Chapter 9 Table 8 resistances on 120 V, not a lab score for a named reel. At 25 and 50 feet, 12 AWG is the default. A short 14 AWG run is close on paper and still the wrong aisle for a motor that runs the whole driveway — see 12 vs 14. At 100 feet, 10 AWG is the honest 15 A answer — the 100-foot guide and 10 vs 12.

Why a thin cord trips and heats

Voltage drop is a resistor you can hold. On start, and again under a long spray, the motor asks for more current than a work light. A thin, long cord drops more volts, so the pump sees less voltage when it needs more amps. Current stays high, copper I²R heat rises along the run, wet contacts warm, and a garage or outdoor GFCI opens. The jacket can be warm the whole length, not just at a loose plug. That is a gauge-and-length problem, not a “weak washer.”

Leaving the reel coiled under that load makes it worse. Unspool what you are using. Two thin 50-foot cords chained together are a 100-foot drop plus extra wet contacts — see daisy-chaining. Buy one cord in the gauge the load wants.

Outdoor jacket is SJTW — not thicker copper

A pressure washer lives in spray, puddles, and sun. Buy a weather-rated jacket in the gauge you already chose: SJTW (or a harder outdoor type). The W letter keeps water and UV from eating the insulation. It does not add copper. A 16 AWG “outdoor” Halloween-light reel is correctly outdoor-rated and still the wrong product. Keep connections off the wet concrete where you can. A thicker cord is not a GFCI.

12 AWG default, 10 AWG on a long driveway

12 AWG is the default for a 13–15 A electric washer at 25–50 feet: one outdoor reel that can take the start hit and a continuous spray without being the weak link. Step up to 10 AWG when the run is a full 100 feet — house outlet to the far curb, a second bay, a boat — when lights already dip on a 12 AWG start, or when the washer lives on the cord all afternoon. 14 AWG is already the wrong aisle past a short run.

Circuit and wet work, not just AWG

• A 15 A washer wants a 15 A or 20 A circuit that is not already running a heater or a compressor. Two 15 A motors on one 15 A breaker is how driveways invent trips.
• GFCI protection outdoors is normal. A thicker cord does not fix a tired GFCI.
• Match the plug to the receptacle. Filing a 20 A blade to fit 15 A is how people invent a fire.
• Indoor SJT stays indoors. Driveway work is SJTW in the gauge you already chose.

Signs the cord is too thin

• The motor hums and will not start, or pressure sags in a normal spray then recovers when you let off the trigger.
• Lights on the same circuit dip when the washer starts.
• The breaker or GFCI trips on start, then holds if you plug in at the wall.
• The cord jacket is warm along the run, not just at a loose or wet plug.

Those signs can also mean a clogged nozzle, a kinked hose, or a tired GFCI. Check the washer. Then check gauge and length.

What “best” does not mean here

We are not ranking brands and we do not have a 9.4. A 12 AWG, 50-foot, SJTW cord with intact 15 A ends from a known listing is the product for a typical electric washer. Brand paint, lighted ends, and a retractable reel are convenience. They are not a substitute for copper, and a 16 AWG “heavy duty” outdoor reel is still 16 AWG.