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Recognizing Connected Load in a 1968 Countryside House with 3-Phase

willy1986 48211 34
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Can my existing 3-phase household connection in a 1968 countryside house handle a future 15 kW motor, and how do I check the available connection power?

No — with a 14 kW connection, your installation is probably too small for a 15 kW motor, especially if other household loads run at the same time, so you should first verify the contracted connection power and the pre-meter protection size with the utility. The forum advice is to check the contract with the power company or call the ZE hotline using your customer number, and to have an electrician inspect the installation on site [#7708370][#7708639] One reply states that to start a 15 kW motor you need to increase the connection power and the pre-meter protection to at least 32 A; otherwise the motor will not start even with star/delta starting [#7718614] Another post estimates the motor current at about 25 A in operation, around 35 A during star start, and roughly 150 A during delta start, while a more detailed calculation gives about 213.6 A starting current for a 15 kW motor [#7722213][#8471853] The utility may charge about PLN 130–150 per additional kW, and one reply notes that in G11 the monthly fixed fee does not increase, only the one-time increase fee is paid [#7718466][#7718614]
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  • #31 8387697
    Informacja
    Level 18  
    Posts: 369
    Help: 2
    Rate: 26
    The power measured by the meter is the current times the voltage.
    And the current can be reduced by connecting a capacitor of appropriate capacity in parallel to the motor.
    By the way, such a receiver, due to the lower current consumption, suffices with smaller protections and thinner cables.
    Too much translation.
    I suggest reading about reactive power compensation.
    There are bundles of this on the internet for all levels of knowledge.
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  • #32 8388804
    marian_em
    Level 25  
    Posts: 843
    Help: 60
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    A "normal" meter measures active power, so you can load a 500kvar battery on the wall and your bill will not decrease. As far as I'm not mistaken, these bill cutters from Allegro have just a capacitor inside:]
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  • #33 8389526
    Miwhoo
    Electric installations specialist  
    Posts: 2137
    Help: 128
    Rate: 315
    Since it is already dimmed, when someone is welding, when you start this engine, you will turn off the lights for a few seconds in the entire village :D

    Are you far from the transformer?

    As for the fees, the topic is freshly reheated, so about PLN 120-130 for each kW I think, additionally an increase in transmission and something else, I do not remember exactly ...
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  • #34 8471853
    troll21
    Level 11  
    Posts: 29
    Rate: 13
    Exactly. He will pay about PLN 130 for each "new" kW. And the fixed fee for power will increase, which below 40kW is probably about PLN 1 per kW. However, the starting current of an exemplary motor with the following data: 15kW, In = 26.7A; Ir / In = 8 cos phi = 0.9 will therefore be 213.6A (immediately in the triangle). On the other hand, Markiewicz gives an AM 32A insert for a 15kW motor with star / delta starting, and aM 63A with direct starting. At the same time, I wonder where I would give such an insert? Because not right behind the counter, right? Because it is not a full-range cartridge (gG, gL). So another problem for me. There would have to be some good motor protection (maybe electronic? Eg MiniMUZ-SR - but how much does it cost? Probably more than this motor). However, when it comes to compensation, it is really an exaggeration. Indeed, the current module responsible for the voltage drop will drop and the active power losses caused by reactive power (dPq) will decrease, but at Pn = 15kW, it is hair-splitting. After all, if a colleague buys a 15kW motor for about PLN 1000- 1200, he will also buy a 4mm2 cable or better and will not connect this motor 1000m from the connector, right?
  • #35 8512665
    troll21
    Level 11  
    Posts: 29
    Rate: 13
    The connection power of my building is 3.4kW, even though I have the main single-phase protection with a 25A fuse with an unknown designation (seal), so theoretically, if I also mounted a 25A meter, I could get 5750W on pure resistance. And on the security I have (16A) 3680W. And hence, it is close to the 3.4 kW in the contract. Also, when it comes to ZE's concern about what's behind the meter (for the first security behind the meter), I think it is justified. Because I have heard that some EVs seal (!) The first advance security. My ZE does not do this, could someone deny or confirm this rumor? I can see that the topic of our discussion is "building connection power", so I am giving this example because it shows that the rated current of the fuses in the connection is not of key importance. The more so because I have an electronic counter, although I do not know if it has a memory of max 15-minute power. If it has (although it does not display such data), even if I had all the fuses on the connection adapted to the 15kW (32A) motor, I would still be in a dot by this meter. Because I would not like to pay a penalty for exceeding the contractual power. The more so I do not understand how people in my village put on heaters
    of water 3F 21kW or 25kW (the fact that it is pure resistance) and ZE says it is OK. Is it OK when it comes to the connected power? Because when I asked ZE if I could theoretically install a 3F connection with a power of 25kW + 3kW that now has (I mean the receivers what I have now + the mentioned water heater), they laughed at me and said that if he wanted to get such power, they would have to check if they got it will withstand (!) and whether the nN line (i.e. 70mm2) will do it (!). Come on. I don't understand this approach. It follows that people plug in whatever they want, "pad the plugs", THAT they don't know anything; and everyone is satisfied ... Trafo somehow works well (I think 100kVA for about 20 - 30 municipal consumers + one small industry).
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Topic summary

✨ The discussion revolves around the electrical capacity of a 1968 countryside house with a 3-phase installation, specifically regarding the feasibility of operating a 15 kW motor. The original poster is uncertain about the existing connection power, which is indicated to be 14 kW, and seeks advice on whether this is sufficient for the intended motor use. Participants suggest checking the contract with the power provider for connection details and recommend consulting an electrician for a site assessment. Concerns are raised about the starting current of the motor, which can reach up to 150A, and the potential need for upgrading the connection power to accommodate the motor's demands. The conversation also touches on the costs associated with increasing power capacity and the implications of reactive power on electricity bills. Additionally, the importance of proper fusing and the potential for voltage drops during motor startup are highlighted.
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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

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, post #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]

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?

  1. Fit a star-delta starter or soft-starter (Schneider, Danfoss).
  2. Keep cable runs short and ≥ 6 mm² Cu.
  3. 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, post #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?

  1. Submit written request with new 20 kW load list.
  2. Pay quoted connection fee (≈ PLN 720–900).
  3. Utility replaces seals, installs 32 A NH fuses, and updates contract—work must be done by a licensed electrician [Elektroda, Qnt, post #7718614]
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