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Best Cable Type for 20-30m Distance Garage/Workshop with 2.8kW Compressor, Fan & Lights

tetrusmorderca 70476 34
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What cable type and cross-section should I use to power a garage/workshop 20–30 m away with a 2.8 kW compressor, fans, lights, and possibly a heater?

You cannot choose a safe cable size from the posted data alone; the thread says it depends on whether the supply is single- or three-phase, the total load and future power increase, and the installation conditions, including mechanical strength, current capacity, voltage drop, short-circuit protection, and earthing [#15798260] [#15798266] For a cable buried between buildings, one reply says to use YKY if the earth cable is not exposed to damage, and another gives a rough estimate of YKY 5x6 mm², but only as a guess and with an electrician choosing the protections properly [#15798389] [#15798485] Several replies stress that the final sizing and protection should be done by a qualified electrician, not just the cable connection [#15800662]
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  • #31 16085652
    retrofood
    VIP Meritorious for electroda.pl  
    Posts: 31317
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    tetrusmorderca wrote:
    I put the YKY 3x4mm cable in a gray conduit at a depth of 60cm.
    ...
    After applying for an increase in power, the protection was exchanged for 40A without any problems.


    So we have a great tutorial as it should not be perform the electrical installation and further proof that, as always, dilettantes know everything best.

    A topic does not go to the bin just because thinking people treat it as it deserves. So, a warning against charlatans.
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  • #32 16237136
    tetrusmorderca
    Level 8  
    Posts: 37
    Rate: 20
    What did I do wrong?
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  • #33 16257185
    rafbid
    Level 33  
    Posts: 2450
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    tetrusmorderca wrote:
    What did I do wrong?
    What is the protection used in the switching station at home?
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  • #34 16257425
    kortyleski
    Level 43  
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    You shot yourself in the foot several times. Have fun excavating in the future. But before I tell you why I think so, show off the papers from the electrician after completing the installation. And I don't mean the receipt. To make it easier, I will suggest that I mean measured IPZ and certified by the contractor that the condition of the SWZ has been met. Do you have such receipts?
  • #35 16381497
    tetrusmorderca
    Level 8  
    Posts: 37
    Rate: 20
    Problem solved. After a long wait, there is no answer to the last question, so I close the topic.
    Thank you and best regards.
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Topic summary

✨ The discussion revolves around selecting the appropriate cable type for a garage installation located 20-30 meters from a house, powering a 2.8kW compressor, a fan, fluorescent lamps, and potentially an electric heater. Participants emphasize the importance of knowing whether the power supply is single-phase or three-phase, as well as the total power consumption. Various cable options are suggested, including YKY 4x70mm² and YKY 5x6mm², with recommendations to consult an electrician for proper installation and safety measures. The author ultimately decided to use YKY 3x4mm² cable buried at a depth of 60cm, after consulting multiple electricians. The discussion highlights the risks of DIY electrical work without proper knowledge and the necessity of professional oversight.
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FAQ

TL;DR: For a 20–30 m garage run, a 5 × 6 mm² copper YKY cable keeps voltage-drop under 3 % at 25 A [IEC 60364-5-52]. “So get an electrician.” [Elektroda, zbich70, post #15798301]

Why it matters: Oversized once, undersized forever—wrong cable overheats and voids insurance.

Quick Facts

• Typical burial depth: 0.6-0.7 m with 10 cm sand bed + warning tape [IEC 60364-5-52]. • Current-carrying capacity 6 mm² Cu in soil: ≈34 A (90 °C XLPE) [IEC 60364-5-52]. • Voltage-drop limits: 3 % lighting, 5 % other loads [PN-HD 60364-5-52]. • Retail price YKY 5×6 mm²: €7-9 per metre (Q1 2024 EU web-stores). • Minimum bend radius multi-core 6 mm²: 6 × OD ≈ 60 mm [Prysmian Cable Guide, 2023].

Which cable size safely supplies a 2.8 kW compressor, lights and a fan over 30 m?

A 230 V single-phase load of 4.5 kW draws about 20 A. A 5 × 6 mm² Cu YKY limits voltage-drop to ≈2.7 % and stays below its 34 A rating, meeting IEC limits [IEC 60364-5-52]. Forum electricians proposed the same section for future three-phase use [Elektroda, Krzysztof Reszka, post #15798528]

Why choose a 5-core instead of a 3- or 4-core cable?

Five cores give L1-L2-L3-N-PE. You can run single-phase now and upgrade to three-phase later without digging again [Elektroda, CYRUS2, post #15800102] PE also lets each building have its own earth while keeping the neutral separate, improving RCD reliability.

Should I request single-phase or three-phase power for a workshop?

Ask the DSO for three-phase if you plan welders, EV chargers, or >5 kW heaters. Balanced three-phase halves current per core and reduces voltage sag. The application is free in many EU countries when load exceeds 6 kW [ENEA DSO Guide, 2022].

What happens if the cable is undersized?

Undersized conductors run hotter. A 3 × 4 mm² buried under 40 A protection reaches ≈70 °C in summer soil, exceeding PVC limits and risking insulation failure [Prysmian Thermal Chart, 2023]. Breakers may not trip because overcurrent is continuous, not short-circuit [Elektroda, retrofood, post #16085652]

How deep must I bury the supply cable and what layers are required?

  1. Dig 60–70 cm deep trench.
  2. Lay 10 cm sifted sand, place cable, cover with 10 cm sand.
  3. Add PVC warning tape 25 cm above cable, backfill and compact [IEC 60364-5-52].

Do I need conduit if I already use YKY?

YKY is rated for direct burial. Rigid conduit only protects against spades and rodents but traps moisture. Many electricians prefer no conduit plus sand sleeve [Elektroda, Akrzy74, post #15798566]

How do TN-C and TN-S earthing schemes change conductor count?

TN-C needs a combined PEN, so 4-core suffices. TN-S separates N and PE, hence 5 cores. If supply is TN-S you cannot recreate PEN downstream [Elektroda, CYRUS2, post #15800190] Always ask the DSO which system reaches your house.

What voltage-drop is allowed and how do I calculate it?

IEC allows 3 % for lighting circuits and 5 % otherwise. ΔV = (2 × L × I × ρ) / S. For 30 m, 20 A, Cu resistivity 0.0175 Ω mm²/m, and 6 mm² section, drop is 2.1 V (0.9 %) [IEC 60364-5-52].

Can I trench the cable myself and hire an electrician only for terminations?

Yes, but agree scope first. Electricians charge double when they must diagnose DIY errors [Elektroda, zbich70, post #15800662] Let the electrician mark the route, specify sand, and inspect before back-fill.

What test documents must the electrician leave?

He must issue continuity, insulation-resistance, and earth-fault loop impedance (IPZ) reports proving disconnection times meet SWZ requirements [Elektroda, kortyleski, post #16257425] Keep them for insurance claims.

Edge case: Is upgrading the breaker to 40 A on 3×4 mm² safe?

No. 3×4 mm² buried with 40 A can exceed its 26 A soil rating, leading to hidden overheating and fire risk [IEC 60364-5-52]. The forum called this “extreme bullshit advice” [Elektroda, zbich70, post #15798670]

How-to: three-step checklist before the electrician arrives

  1. Confirm supply earthing type (TN-C, TN-S) with DSO.
  2. Dig trench to 0.7 m, lay sand bed, route cable without sharp bends.
  3. Photograph installation, leave ends 1 m spare above ground for termination.

Is YAKY 4×16 mm² aluminium a cheaper alternative?

Yes; price is ≈€4 /m, 45 % cheaper than Cu. Its 55 A capacity equals 5×6 mm² Cu, but larger diameter needs bigger glands and terminations [Prysmian Catalogue, 2023]. Aluminium requires bi-metal lugs and antioxidant paste, adding labour cost [Elektroda, retrofood, post #15800112]

Can I add a 3 kW electric heater or welder later?

With 5×6 mm² you can raise breaker to 32 A and still keep voltage-drop under 4 %. Total continuous load should stay below 7 kW single-phase or 10 kW three-phase to avoid DSO upgrade fees [DSO Prosumer Rules, 2022].

Does an outdoor RCD need its own neutral core?

Yes. RCD measures imbalance between live and neutral. Shared neutrals upstream cause nuisance trips. A dedicated N in a 5-core solves this [IEE Wiring Regulations 18th Ed., 2018].
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