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Selecting the Right Cable Gauge for a 3.3kW STIHL Pressure Washer Over 30m Distance

piotr zieliński 51410 21
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Can a 30 m 3×1.5 mm² extension cord cause a 3.3 kW pressure washer motor to overheat or burn out, and what cable cross-section should be used instead?

A 30 m 3×1.5 mm² extension is too small for a 3.3 kW single-phase washer; a 3×2.5 mm² cable was recommended as sufficient for that load and length [#6072905] A too-thin cable can create enough voltage drop that the motor receives much less than 230 V, runs weaker, draws load like full power, and heats up more, especially if plugs or sockets have poor contact [#6062171] The rated current for such a motor was estimated at about 18 A, so the cable and connections need to handle a fairly high current [#6066856] However, several replies note that the washer should have overload protection, and if it does not trip under undervoltage or overload, the protection may be missing or faulty rather than the extension cord being the only cause [#6081882][#6073350]
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  • #1 6062048
    piotr zieliński
    Level 11  
    Posts: 7
    Rate: 5
    Colleagues, I am asking for help. I have a STIHL pressure washer. The 3.3 kW engine burned out. The website stated that it burned down because the extension to the washer, about 30 meters long, was made of a 3x1.5 kw cable. Is it possible?
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  • #2 6062104
    spinacz
    Level 42  
    Posts: 8524
    Help: 1192
    Rate: 2616
    Total rubbish, the cross section of the wires in the extension cord cannot cause the motor to burn out.
  • #3 6062171
    zibq
    Level 28  
    Posts: 1017
    Help: 83
    Rate: 181
    spinacz wrote:
    Total rubbish, the cross section of the wires in the extension cord can not cause the motor to burn out.


    I would argue. Take into account the voltage drop (1.5mm kW is not enough for this power), throw in poorly twisted plugs / sockets and it turns out that the motor gets, for example, 150V instead of 230V. How will the engine behave when the voltage is lowered? It will be weaker + load as for full power = more heat, less cooling. It is only a matter of time before the winding burns out.
  • #4 6062369
    spinacz
    Level 42  
    Posts: 8524
    Help: 1192
    Rate: 2616
    Well, you're right, buddy, maybe I wrote too sharply, but I suspect that the contact you are talking about with a poorly twisted than a burnt engine would get stoned sooner.
  • #5 6063109
    krzys10000
    Level 2  
    Posts: 2
    Rate: 1
    With this length it must be 2.5mm square. I had a similar case. For the future, buy a karcher washcloth - on this cross-section and with this length of the extension cord you will not start at all, and at 2.5mm sq. It flies like this doll.
  • #6 6066221
    piotr zieliński
    Level 11  
    Posts: 7
    Rate: 5
    I do not have this washer, it is on the site, but what do you think can be the nominal current with such a large single-phase 3.3kW motor.
  • #7 6066728
    Rafik4
    Level 31  
    Posts: 1108
    Help: 214
    Rate: 313
    Probably around 14A.
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  • #8 6066856
    ergonus
    Level 15  
    Posts: 80
    Help: 13
    Rate: 18
    14A, assuming that cos phi = 1 and it certainly is not ... for such a motor, the rated current will be about 18 A
  • #9 6072292
    elektryk13a
    Level 19  
    Posts: 432
    Help: 3
    Rate: 46
    I propose to calculate the voltage drop on a 1.5mm cable and a length of 30m. I understand it's a copper cable. I guarantee it's not 80V.
  • #10 6072905
    grexx
    Level 11  
    Posts: 4
    Rate: 6
    I recommend the site Link , there is a formula for calculating the minimum wire diameter for a given voltage drop. According to my calculations, 3x2.5 mm2 is enough for this washer with your assumptions and the efficiency of the 3.3 kW motor is 0.81.
  • #11 6072960
    jurekN
    Level 23  
    Posts: 566
    Help: 33
    Rate: 116
    That 3X 2.5mm is no doubt and if the service saw a 3X 1.5mm extension cord and the washer is under warranty, they will not recognize this warranty, and what was the cause of the engine burned, you can only guess.
  • #12 6073350
    elektryk13a
    Level 19  
    Posts: 432
    Help: 3
    Rate: 46
    The question was whether the 1.5mm cable damaged this device. In my opinion, a 10% chance of it. And what the cable should be, the producers probably know better. And the fact that the website did the topic in its favor in 3 minutes is a different matter.
    Even if they were sure it was their fault, it would be easier to push it onto the customer.
    But unfortunately the user has no chance of defense in this case.
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  • #13 6074303
    piotr zieliński
    Level 11  
    Posts: 7
    Rate: 5
    But why is there not a word about it in the manual. The user does not need to have an electrical education and know that the extension must use a 2.5mm square cable.
  • #14 6078417
    ubeczek
    Level 11  
    Posts: 11
    Rate: 4
    I may be wrong, but the important thing is whether this 30-meter cable was developed. because if it was not fully developed, a coil could be created.
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  • #15 6078860
    Lol 123456
    Level 13  
    Posts: 57
    Help: 2
    Rate: 6
    hmm, and what will happen when such a coil is created?
  • #16 6078924
    ergonus
    Level 15  
    Posts: 80
    Help: 13
    Rate: 18
    Note that there are two cores in the coiled cable and if the device works correctly, one wire will "flow" into the device and the other will "flow out" ... and thus the induced magnetic fields cancel out ...
  • #17 6081882
    P_Kamil
    Level 2  
    Posts: 2
    Hello colleagues
    You are too deep about the extension cord.
    The 3.3kW motor with single-phase power is a bit big and strange (unnormalized) power (it can take about 20A). For single-phase power, the largest typical motor is 2.2kW.
    But the question is different: why is the motor in the device not protected against overload (motor switch, thermal relay).
    When the supply voltage drops, the motor consumes more current - when the rated value of the motor is exceeded, the protection must switch it off. In this way, it is not allowed to operate in abnormal conditions and damage the engine.
    So, either there is no security or it is malfunctioning.
    Don't get in the service - it's not an extension cord.
  • #18 6084397
    A-Mail
    Level 23  
    Posts: 740
    Help: 22
    Rate: 214
    ergonus wrote:
    Note that there are two cores in the coiled cable and if the device works correctly, one wire will "flow" into the device and the other will "flow out" ... and thus the induced magnetic fields cancel out ...

    Magnetic fields cancel out, but a coiled cable can transfer 40% of what is unrolled If you let go of 10 through such a coil, you have a nice heater
    But why did you tell the service technicians that you worked on an extension cord?
  • #19 6086095
    pinokio14
    Level 12  
    Posts: 40
    Help: 1
    Rate: 14
    and are you sure the washer is single-phase? whether the cable cross-section for the extension cord is specified in the manual
  • #20 6086162
    A-Mail
    Level 23  
    Posts: 740
    Help: 22
    Rate: 214
    If the washer was 3-phase, how would it be connected to a 1-phase extension cable?
    Of course I am, but you have to get a bit of work and want it very much! With this 3.3 KW, I would be wondering
    Maybe the type of washer we'll find out?
  • #21 6086244
    jurekN
    Level 23  
    Posts: 566
    Help: 33
    Rate: 116
    The discussion on this topic becomes pointless, so I am asking you to close it, because it will not bring anything in anyway.
  • #22 6088620
    piotr zieliński
    Level 11  
    Posts: 7
    Rate: 5
    Okay, colleagues, I am very glad that you answered my question so spontaneously. There is no doubt that the installation should be changed to 2.5 kw. I will do so and thank you once again and close the topic. Hi
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Topic summary

✨ The discussion centers around the appropriate cable gauge for a 3.3 kW STIHL pressure washer when using a 30-meter extension cord. Concerns were raised about the potential for motor burnout due to using a 3x1.5 mm² cable, with participants debating the impact of voltage drop and current load. It was concluded that a 2.5 mm² cable is necessary to prevent overheating and ensure proper operation. The nominal current for the motor was estimated to be around 18A, and the importance of using the correct cable gauge was emphasized to avoid warranty issues and equipment damage. The conversation also touched on the lack of clear guidelines in the user manual regarding cable specifications.
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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?

  1. Double the run length (out + back).
  2. Find conductor resistance (Ω/m) from IEC 60228.
  3. 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?

  1. Measure no-load voltage at socket (should be ~230 V).
  2. Start washer; measure voltage under load.
  3. 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]
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