FAQ
TL;DR: Starting a 15 kW compressor motor can pull 150 A on direct-on-line start [Elektroda, Mariuszczs, post #7722213]; “pure tragedy” for weak rural lines, warns cranky [Elektroda, cranky, post #7733111] Verify your contract power first or upgrade to 20 kW and 32 A fuses before energising.
Why it matters: Oversized inrush current can black-out your neighbours and breach your utility agreement.
Quick Facts
- Rural homes often have 3 × 20 A pre-meter fuses, giving ≈ 14 kW of contracted power [Elektroda, willy1986, post #7718036]
- Utility upgrade fee: PLN 120–150 for each extra kW ordered [Elektroda, retrofood, post #7718466][Elektroda, Miwhoo, post #8389526]
- 15 kW/400 V motor: rated 26–27 A, star start ≈ 35 A, direct start ≈ 150 A [Elektroda, Mariuszczs, post #7722213]
- Minimum recommended pre-meter protection for star/delta start: 32 A, 3-pole [Elektroda, Qnt, post #7718614]
- 4 mm² Al overhead line stays within 3 % voltage drop for ≤ 25 A over about 40 m (Voltage-Drop Tables).
How do I check the official connection power for my house?
Look at your supply contract or call the utility (ZE) with your customer number; they will tell you the contracted power and fuse size [Elektroda, Łukasz-O, #7708639].
Three fuses marked L20 A, L20 A, L16 A sit by my meter—what power does this indicate?
A 3 × 20 A set limits continuous three-phase load to about 14 kW (√3 × 400 V × 20 A ≈ 13.8 kW) [Elektroda, willy1986, post #7708395]
Can my 1968 overhead 3-phase supply start a 15 kW motor safely?
Not with 20 A fuses; the 150 A inrush would trip them and cause village-wide dips. Upgrade to 32 A pre-meter protection and at least 20 kW contract power [Elektroda, Qnt, post #7718614][Elektroda, Mariuszczs, post #7722213]
What running and starting current should I expect from a 15 kW, 400 V motor?
Rated current is roughly 26 A. Star start draws ≈ 35 A, direct start ≈ 150 A—about six times rated [Elektroda, Mariuszczs, post #7722213]
How much will it cost to raise my supply from 14 kW to 20 kW?
Utilities charge PLN 120–150 per additional kW, so +6 kW costs about PLN 720–900, plus a small one-time administrative fee [Elektroda, retrofood, post #7718466]
Do I need to tell the utility that the new load is a compressor motor?
Yes. ZE can reject upgrades if the load is classed as ‘service’ rather than household use, forcing a business tariff [Elektroda, retrofood, post #7718740]
Why do lights dim or TVs reset when large motors start?
Motor inrush drags voltage down on thin rural lines; users report kettles and welders already dimming lights on 25 mm² conductors [Elektroda, Mariuszczs, post #7734012]
What can I do to cut start-up current spikes?
- Fit a star-delta starter or soft-starter (Schneider, Danfoss).
- Keep cable runs short and ≥ 6 mm² Cu.
- Start with unloaded compressor if possible. "Soft-start is better," notes cranky [Elektroda, cranky, post #7733111]
Is power-factor compensation with capacitors worthwhile on a home tariff?
No savings under G11 because the meter bills only active kWh; a 500 kvar capacitor cuts no cost [Elektroda, marian_em, post #8388804]
Could the utility seal post-meter fuses, and what if I swap them?
ZE sometimes seals post-meter breakers as current limiters. Breaking the seal is tampering and risks penalties [Elektroda, Łukasz-O, #7719252].
How do I size cables and protections for a 15 kW motor?
Use 5-core 6 mm² Cu or 10 mm² Al up to 30 m, protected by 32 A gG at the main panel and a-M 32 A motor fuse per Markiewicz tables [Elektroda, troll21, post #8471853]
What’s an edge case where the utility refuses the motor connection?
If measured dips exceed 5 % or the motor exceeds 11 kW limit for household class, ZE can demand a separate business connection [Elektroda, Mariuszczs, post #7718979]
3-step guide: upgrading to 32 A pre-meter fuses?
- Submit written request with new 20 kW load list.
- Pay quoted connection fee (≈ PLN 720–900).
- Utility replaces seals, installs 32 A NH fuses, and updates contract—work must be done by a licensed electrician [Elektroda, Qnt, post #7718614]
