FAQ
TL;DR: A 3.3 kW washer can pull ~18 A, and “3×2.5 mm² is no doubt” [Elektroda, ergonus, #6066856; jurekN, #6072960]. Undersized 3×1.5 mm² over 30 m can drop >5 % of voltage, overheat, and void warranty. Why it matters: choosing the right cord avoids burnt motors and lost guarantees.
Quick Facts
• Continuous current for 3.3 kW/230 V single-phase motor: approx. 18 A (cos φ ≈ 0.9) [Elektroda, ergonus, post #6066856]
• Resistance of 30 m run (60 m loop) in 1.5 mm² Cu: ≈ 0.70 Ω [*IEC 60228*].
• Resulting voltage drop at 18 A: ≈ 12.6 V (5.5 %)—over the 5 % portable-equipment limit [IEC 60364-5-52].
• 3×2.5 mm² drops only ≈ 7.6 V (3.3 %), keeping you within spec [*ResCalc*].
• Coiled cable derates capacity to about 60 %—acts like a heater [Elektroda, A-Mail, post #6084397]
What cable size should I use for a 3.3 kW STIHL washer over 30 m?
Use a 3-core 2.5 mm² copper extension. It holds 18 A with <5 % voltage drop and meets IEC 60364 limits [Elektroda, jurekN, #6072960; IEC 60364-5-52].
Can a thin 1.5 mm² cord really burn out the motor?
Yes. At 18 A the voltage can sag to ~217 V, the motor draws more current, heats, and its fan cools less. Repeated stress can char windings [Elektroda, zibq, post #6062171]
How much current does a 3.3 kW single-phase motor draw?
Rated current ≈ 18 A at 230 V and cos φ 0.9; start-up inrush may hit 5 × rated (>90 A) for a few cycles [Elektroda, ergonus, #6066856; Siemens Motor Guide].
How do I calculate voltage drop for an extension?
- Double the run length (out + back).
- Find conductor resistance (Ω/m) from IEC 60228.
- Voltage drop = I × R.
Example: 60 m of 1.5 mm² (0.0117 Ω/m) → 0.70 Ω; at 18 A drop ≈ 12.6 V [ResCalc].
What happens if I leave the extension cable coiled?
Coiling creates a compact inductor that traps heat. Capacity falls to ~60 %, so 18 A through 1.5 mm² can turn the reel into a 200 W heater [Elektroda, A-Mail, post #6084397]
Will using 1.5 mm² always void my warranty?
Many service centres deny claims when the cord is under-sized because manuals specify ‘suitable conductors’. Evidence of 1.5 mm² gave grounds to reject repair in the forum case [Elektroda, jurekN, post #6072960]
Are there protections that stop low-voltage burnout?
A motor-rated thermal overload or electronic undervoltage relay trips when current rises 10–20 % over FLA, preventing damage. The washer in the thread lacked or had faulty protection [Elektroda, P_Kamil, post #6081882]
Is a 3.3 kW single-phase motor unusual?
Yes. Standard IEC frames top out at 2.2 kW on 230 V. Larger powers need custom windings and higher start currents, stressing cables [Elektroda, P_Kamil, #6081882; ABB Catalog].
How can I quickly test if my extension is good enough?
- Measure no-load voltage at socket (should be ~230 V).
- Start washer; measure voltage under load.
- If drop exceeds 11 V (5 %), switch to thicker cord [IEC 60364-5-52].
Which outdoor extension reels come with 2.5 mm² cable?
Brennenstuhl Garant, Masterplug Pro-XT, and Karcher Premium reels ship with 3 × 2.5 mm² HO7RN-F cable rated 25–30 A, IP44 splash-proof [Manufacturer datasheets, 2023].
Will the washer start on 1.5 mm² but trip later?
Edge-case: it may start when cold but stall after 5 min; copper warms, resistance rises 40 %, voltage dips further, overload trips or motor overheats [Copper Dev.].
Does leaving the cord partially unrolled affect magnetic fields?
Magnetic fields in a two-wire coil cancel, so inductive heating is minor. Heat build-up stems from I²R losses with no airflow [Elektroda, ergonus, post #6078924]
