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Dim Light in New Installation: Voltage Drop to 225V with Electric Kettle, 100W Bulb, 500/16 Fuse

sapsapl 44511 28
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Why do the lights dim and the voltage drop from about 230 V to 225 V when a kettle or refrigerator starts in a newly renovated apartment, and how can I tell whether the fault is in the apartment wiring or in the supply side?

A slight dimming and a small voltage drop under load usually points to a poor connection, undersized wiring, or a fault upstream of the apartment rather than a normal effect of a correctly made installation [#12401156][#12401752] The thread’s best advice is to measure the short-circuit loop/impedance (LN) at several points: at the dimming lamp, the loaded socket, junction boxes, the switchboard input and outputs, and at the apartment feeder/WLZ; compare the results with what should be expected from the cable length and cross-section, because a large mismatch suggests a bad contact [#12404035] If the problem is already present at the building supply or at the boundary between the utility and the building, the building administrator/community or the network operator should be involved, since the fault may be in the WLZ or outside the apartment [#12813930][#12401752] The 10 A “differential” is likely incorrect for a circuit protected by 16 A fuses, but replacing it is not the real fix if the dimming remains when the differential is bypassed [#12401880][#12402113] The circuits should also be checked against the actual wire cross-sections and separation of lighting and sockets, because mixed or poorly loaded circuits can make the symptom worse [#12403992][#12432719]
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  • #1 12401132
    sapsapl
    Level 10  
    Posts: 45
    Rate: 29
    Hello,

    I have a problem. The apartment has undergone a major renovation, but I have an objection to the electrician.
    There is 230-232 V in the apartment, 500/16 fuse (new)
    Depending on the room, sockets are located on different circuits, lighting also on other circuits.

    The problem is that when you turn on, for example, the aggregator from the refrigerator, and even more so, the electric kettle, the light bulb dies slightly (so far the traditional 100W). There is also a slight voltage drop to around 225V.

    Should this be the case in a new installation? Is there any way to confirm that the wrong cables have been inserted (don't know, maybe bad sections?) Or the reason could be something else?
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  • #2 12401156
    korrus666
    Level 40  
    Posts: 5219
    Help: 584
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    The dimming of lights when switching on loads with high power consumption is most often caused by a poor connection at some point in the installation. I would look for fuses in the area or even in front of them.
  • #3 12401180
    sim_
    Level 18  
    Posts: 194
    Help: 22
    Rate: 26
    Hello. First, check the voltage at the entrance to the apartment. If there is a voltage drop during activation, it means that the outdoor installation may be damaged. And the additional question of whether the electrician performed the measurements of the installation after the work was completed. Regards Janek.
  • #4 12401182
    krzysztofh
    Level 29  
    Posts: 1557
    Help: 101
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    And what is WLZ (length and cross-section)?
  • #5 12401258
    .Jack
    Electrician specialist  
    Posts: 1142
    Help: 361
    Rate: 425
    sapsapl wrote:
    however, I have an objection to the electrician.

    Even the best electrician and the best-made electrical installation cannot eliminate poor-quality electricity coming from the power plant or faulty electricity receivers.
    The defect in the form of a poor contact in the electrical system is probably located outside the apartment in the meter board.
    The only solution is to ask the electrician, who did the renovation of the installation in the apartment, to find out the cause. Because the problem will not be solved via the Internet.
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  • #6 12401622
    sapsapl
    Level 10  
    Posts: 45
    Rate: 29
    The sections are supposed to be good (which I do not know, but I asked another electrician how they were served, what they were bought) - I do not know myself :-)

    Currently, a differential for 10A is inserted, the fuse on the cage is 16A (new). Apparently, this difference may be too weak, but does that explain the behavior?

    @ korrus666: As for the connections, they probably can be on the fuses because the lights are put on these temporary holders, so I guess it's out - another electrician tightened the connections on the fuses yesterday.

    @sim_: of course not; - / Full professed

    @krzysztofh: Unfortunately, I don't know

    @ .Jack: I'm sure you are right, but I try to find potential causes so that I don't stand like a pillar of salt when I require something from an electrician.

    First of all, I still do not know if such a decrease can occur in a well-made installation?
  • #7 12401659
    Anonymous
    Anonymous  
  • #8 12401671
    .Jack
    Electrician specialist  
    Posts: 1142
    Help: 361
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    sapsapl wrote:
    is such a drop allowed to occur in a well-made installation?

    He has the right to perform.
    Electrical installation is an extension of the power grid from the transformer. If this is loaded to the maximum, each time the next receiver is turned on, the voltage drops. But this is already the responsibility of the Power Plant.
    Regarding the installation, the electrician will detect whether the fault is on the side of the power supply or the electrical installation, because it may be hot, loose or tight contact on the N or L cable. And therefore it is important to visit a specialist to see who to complain to and from whom to demand quality improvement electricity without flickering light.
    Interference may also be caused by the refrigerator unit itself with a damaged anti-interference filter.
  • #9 12401752
    robin161
    Level 25  
    Posts: 529
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    krzysztofh wrote:
    Quote:
    And what is the WLZ (length and cross-section)?

    I would add - ... and in what condition is it? What is the power allocation for the apartment? The post shows that this is a secondary market apartment in a multi-family house - right?
    I know from practice that, as a rule, the power allocation for an apartment was 4 kW. After years of operation and loading with receivers of significant power by previous tenants, this installation is in a deplorable condition. And here I would be looking for the cause of your troubles. After consulting the electrician who performed the installation for you - report the problem to the building administration.
  • #10 12401836
    sapsapl
    Level 10  
    Posts: 45
    Rate: 29
    @ robin161: the installation from the staircase (apartment in the block) is new. even the cable connecting the fuses and the meter is new.

    @ .Jack: The electrician will say that it is not his fault (I will probably look for another specialist to verify). Can I require ENEA (operator) to remove the defect? Or ask them for measurements? (would it be cheaper to hire a separate electrician from the free market?)

    @ Bronek22: the fridge is new, gorenje (if it matters), the problem arises when turning on the electric kettle, vacuum cleaner (different socket)


    "My" electrician called, he says that the fault may be on the 10A differential side? says inserting a larger one will help. Is it true or crap?
  • #11 12401880
    BILGO
    Level 38  
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    sapsapl wrote:
    "My" electrician called, he says that the fault may be on the 10A differential side? says inserting a larger one will help. Is it true or crap?

    It seems to me that the problem is rather with small cross-sections of the wires ... Or possibly a poor contact at some connection ...

    And as for the "differential". Is it an RCBO or an ordinary RCD?
    If the RCD is 16A for the upstream fuse, the RCD should be greater than or equal to 16A ... rather certainly not less.
  • #12 12401908
    fighter
    Level 21  
    Posts: 396
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    sapsapl wrote:
    Can I require ENEA (operator) to remove the defect? Or ask them for measurements?

    "My" electrician called, he says that the fault may be on the 10A differential side? says inserting a larger one will help. Is it true or crap?


    We do not know what your receivers and power are, but the 10A differential is a bit small, you can give a bigger one, e.g. 16A / 30mA or 20A / 30mA :)

    I think that ENEA will make you verify by measurements and a visit by an electrician with permissions or the recipient's side everything is as it should be, If you prove to them that everything is ok in the house (apartment), then you can demand something from them, the only question is what they said.

    Colleague, we on the forum will not show you 100% of what is the cause of the problem, we can only give you the direction in which you need to follow, but someone has to do it anyway and it is best if it was an electrician.
  • #13 12402113
    sapsapl
    Level 10  
    Posts: 45
    Rate: 29
    We will exchange the differential for sure. The electrician admitted himself that he mistakenly took one and assembled it. The problem was that after omitting the differential in the circuit, the problem was still there.

    I know that there is no need to visit a specialist, but tips like yours are valuable
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  • #14 12402153
    elpapiotr
    Electrician specialist  
    Posts: 12199
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    sapsapl wrote:
    We will replace the differential for sure. The electrician admitted himself that he mistakenly took one and assembled it.
    Exactly. And he probably forgot his glasses to see what he wrote on it.
    Measurement of a short-circuit loop at a socket and at the switchgear input (comparative) will explain everything in a moment.
  • #15 12402998
    Anonymous
    Level 1  
  • #16 12403281
    TWK
    Electrician specialist  
    Posts: 2326
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    sapsapl wrote:
    @sim_: of course not; - / Full professed
    It is worth finding out the cause of the problem by someone with the appropriate measures.

    How many circuits (fuses / switches) are there in the apartment and what are they responsible for? Because if the lighting and socket circuits are mixed up, then such situations with dimming of the lighting occur, especially when powerful receivers are connected to the socket far from the switchgear. But to do so nowadays is against the law.

    sapsapl wrote:
    claims that the fault may be on the 10A differential side?
    Hmm. The smallest RCD current rating I had in my hand was 25A. We will ask for a photo of what is installed in the apartment.
  • #17 12403830
    sapsapl
    Level 10  
    Posts: 45
    Rate: 29
    @TWK: The switchgear has: 9 fuses B16 (605510) Legrand + one differential B16 08402 Legrand. The lighting is definitely on a different fuse than the sockets. Kitchen (as I remember correctly) for 2 + 1 (lighting), the room also divided into zones (for computers) and the rest, etc. So if they are not mixed up (only light on the safe - in several rooms) then it should not be done?

    @ 15kVmaciej: yes, I know, I'll try to arrange one, maybe some list what to ask for?

    @elpapiotr: I will try to take care of these measurements this week. Any other measurements advisable?
  • #18 12403992
    TWK
    Electrician specialist  
    Posts: 2326
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    sapsapl wrote:
    one differential B16 08402 Legrand.
    There is no such difference, probably something more is written. Please provide photos.

    sapsapl wrote:
    9 fuses B16 (605510) Legrand
    There should probably be B10 for lighting ...

    sapsapl wrote:
    So if they are not mixed up (only the light is safe - in several rooms), then it shouldn't be done like that?
    It should not - it means that a possible fault is upstream of the circuit separation (upstream of the switchgear). But again - the measurements will explain where the problem lies.
  • #19 12404009
    Anonymous
    Level 1  
  • #20 12404035
    TWK
    Electrician specialist  
    Posts: 2326
    Help: 220
    Rate: 509
    15kVmaciej wrote:
    For my part, I will propose the measurement of the L-PE loop resistance in the table
    L-PE will not do much, rather LN ...

    I would measure this impedance (or resistance, depending on the meter) successively at the following points:
    - a fading lamp,
    - sockets after the load of which this lamp dims,
    - in places where these circuits are connected (boxes)
    - in the switchgear, both at the output of the circuits and at the input
    - at the terminals of the departure to the apartment from WLZ
    - if there is access, it is available at WLZ on the lower floors

    I propose to compare the results (or rather their differences) with what should come out theoretically (estimation based on the length and cross-section of the conductors) - any greater inconsistency suggests a bad connection. If the IPZ is bad at the point closest to the power supply, you need to notify the electrician from the co-operative / community or EV.
  • #21 12432719
    sapsapl
    Level 10  
    Posts: 45
    Rate: 29
    from the additions that turned out, it turned out that the lighting installation is 1.5 ^ 2, the sockets for the stove, washing machine, refrigerator and computer are 2.5 ^ 2, and the rest (i.e. under the TV), rooms and others are at 1, 5 ^ 2. All these circuits are on fuses 16 (as I wrote earlier).
    They are not combined anywhere. Could this be it ?!

    PS. specialist measurements this week.
  • #22 12487669
    sapsapl
    Level 10  
    Posts: 45
    Rate: 29
    Apparently the measurements have been taken. Everything is supposed to be ok.
    Apparently, the phase on which the apartment is located was crazy, on another phase it is (supposedly) ok - on that one it supposedly even fell to 216V, on this one it is ok.

    Although according to my meter it is the same from 228V to 224V when connecting a kettle (2.5 ^ 2 circuit), measured on 1.5 ^ 2 circuit.

    An electrician suggests a problem on the operator's side.

    Do I need any documents to call the Operator (Enea)? It is probably not normal for the decrease to be ~ 5V, and because of this decrease the light dimmed very slightly, but still?
  • #23 12487886
    gogi20
    Level 24  
    Posts: 794
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    sapsapl wrote:
    Supposedly measurements were taken. All supposedly okay.
    Supposedly the phase where the apartment is in was a mess, the other phase is (supposedly) ok - on that one supposedly it even dropped to 216V, it is ok.

    sapsapl wrote:
    Electrician suggests the problem on the operator's side.
    If the specialist assessed it like that I guess he is right.
    sapsapl wrote:
    It's probably not normal for the drop to be ~ 5V
    Why? It depends on what load. Certainly the voltage will not increase with a higher load. It may be normal, but it's a bit hard to say on the Internet.
  • #24 12813893
    sapsapl
    Level 10  
    Posts: 45
    Rate: 29
    Unfortunately, the problem reappeared, everything that burned down recently (hdmi TV, hdmi amplifier, pc graphics card) replaced, but unfortunately not everything is guaranteed yet.

    When washing the meter, it shows the load at a maximum of 4 A, the current then drops from 230 to even 223V, it is strange that it does not drop at peak moments. on spin it drops to 226, and goes back to 228V.

    Is it worth calling someone from ENEA?
  • #25 12813930
    elpapiotr
    Electrician specialist  
    Posts: 12199
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    Rate: 3508
    Hello.

    It is worth calling the owner / manager of the building, and it is worth taking measurements as close to the property boundary between the ZE and the Recipient (building) as possible, and only then the network operator (Enea).
    Because the problem may be in the building's WLZ, and this needs to be clarified.
    The burning of 1-phase receiving devices suggests the lack of the so-called "zero" on the power supply.

    Turn off the building's main fuses, check the voltage and SWZ on the building's power supply. Check the continuity of the wires at the WLZ.
    If it does not find the cause, check the continuity of the power supply to the apartment.
  • #26 12814073
    sapsapl
    Level 10  
    Posts: 45
    Rate: 29
    elpapiotr wrote:
    Hello.

    It is worth calling the owner / manager of the building, and it is worth taking measurements as close to the property boundary between the ZE and the Recipient (building) as possible, and only then the network operator (Enea).
    Because the problem may be in the building's WLZ, and this needs to be clarified.
    The burning of 1-phase receiving devices suggests the lack of the so-called "zero" on the power supply.

    Turn off the building's main fuses, check the voltage and SWZ on the building's power supply. Check the continuity of the wires at the WLZ.
    If it does not find the cause, check the continuity of the power supply to the apartment.


    The building is a flat in a block of flats, the administrator is the community.

    As for the burning, the graphics, the amplification device, and the HDMI on the TV went, so maybe the current peaks were too frequent and maybe instead of 5V to the HDMI went more as the current jumped, because as I remember correctly, the measurements at home did not show a lack of zero.
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  • #27 12814289
    GBW
    Level 31  
    Posts: 1419
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    TWK wrote:
    15kVmaciej wrote:
    For my part, I will propose the measurement of the L-PE loop resistance in the table
    L-PE will not do much, rather LN ...

    I would measure this impedance (or resistance, depending on the meter) successively at the following points:
    - a fading lamp,
    - sockets after the load of which this lamp dims,
    - in places where these circuits are connected (boxes)
    - in the switchgear, both at the output of the circuits and at the input
    - at the terminals of the departure to the apartment from WLZ
    - if there is access, it is available at WLZ on the lower floors

    I propose to compare the results (or rather their differences) with what should come out theoretically (estimation based on the length and cross-section of the conductors) - any greater inconsistency suggests a bad connection. If the IPZ is bad at the point closest to the power supply, you need to notify the electrician from the co-operative / community or EV.

    Without Accurate Short Circuit Loop Measurements, it's just a fairy tale.
    4 months have passed since June and my colleague has still not provided the measurement results, have they been made or has the case been forgotten?
  • #28 12818727
    sapsapl
    Level 10  
    Posts: 45
    Rate: 29
    GBW wrote:

    4 months have passed since June and my colleague has still not provided the measurement results, have they been made or has the case been forgotten?


    The measurements were taken, in my absence - I did not get anything on the piece of paper. So probably the measurements are worthy.

    How much should decent measurements cost? Maybe you can recommend someone from Poznań.
  • #29 12820939
    GBW
    Level 31  
    Posts: 1419
    Help: 123
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    Since the measurements were made, the community should have a protocol.
    We only have a short circuit loop measurement here, so it should fit in PLN 200.
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Topic summary

✨ The discussion revolves around a voltage drop issue in a newly renovated apartment, where the voltage drops to around 225V when high-power appliances like an electric kettle or refrigerator are turned on, causing lights to dim. Users suggest that the problem may stem from poor connections, inadequate wire cross-sections, or issues with the power supply from the utility company. Recommendations include checking the voltage at the apartment's entrance, ensuring proper measurements of the electrical installation, and verifying the condition of the wiring and connections. The discussion also highlights the importance of consulting a qualified electrician to diagnose the issue accurately and the potential need to contact the power company for further investigation.
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FAQ

TL;DR: A 2 kW kettle draws 8.7 A; voltage sag above 5 % (≈11 V) breaches EN 50160. “Even the best electrician cannot eliminate poor-quality electricity” [Elektroda, .Jack, post #12401258] Diagnose with loop-impedance tests before blaming appliances.

Why it matters: Repeated drops accelerate wear on electronics and signal hidden faults that may start fires.

Quick Facts

• EU supply tolerance: 230 V ±10 % (207–253 V) [EN 50160]. • Permitted voltage drop inside dwelling: 3 % lighting, 5 % socket circuits [IEC 60364-5-52]. • Current-carrying capacity: 1.5 mm² ≈ 15 A; 2.5 mm² ≈ 20 A [PN-HD 60364]. • Short-circuit loop test in Poland: ~200 PLN [Elektroda, GBW, post #12820939] • Refrigerator start-up may reach 6× running current [DOE, 2012].

Is a 5 V drop from 230 V to 225 V acceptable?

Yes, it equals 2.2 %. EN 50160 allows ±10 % so anything above 207 V passes the legal limit. However IEC 60364 recommends keeping final-circuit drops below 5 % (≈11 V), so investigate if loads cause larger sag [EN 50160; IEC 60364-5-52].

Why do lights dim when the fridge or kettle starts?

Motor and heating elements draw high inrush current—4 A for the fridge, 8–9 A for a 2 kW kettle [DOE, 2012]. Any loose, corroded, or undersized connection adds resistance, amplifying the voltage dip [Elektroda, korrus666, post #12401156]

Can a 10 A residual-current device (RCD) cause the dimming?

No. An RCD monitors leakage; its internal resistance is milliohms. Up-rating it to 16 A improves discrimination but does not cure voltage sag [Elektroda, fighter, post #12401908]

How do I pinpoint whether the fault is in the flat or the building?

  1. Measure voltage at the apartment isolator under load.
  2. Repeat at the building’s riser (WLZ) terminals.
  3. Compare results; a large difference means building wiring issues [Elektroda, sim_, post #12401180]

What fuse sizes and cable sections should I have?

Lighting: 1.5 mm² on B10–B13 breakers. Sockets: 2.5 mm² on B16. Dedicated high-power appliances may need 4 mm² on B20–B25 [PN-HD 60364]. Using B16 on a 1.5 mm² lighting line, as reported, exceeds the standard and increases voltage drop [Elektroda, sapsapl, post #12432719]

When should I call the network operator instead of a private electrician?

Call the operator after documented measurements at the supply point show voltage outside 207–253 V or flicker severity exceeding 3 % Pst limit [EN 50160]. Operator must correct upstream issues within 24 h in Poland [URE, 2021].

How do I measure short-circuit loop impedance?

  1. Plug the tester into the most affected socket and record Zs.
  2. Repeat at the distribution board outgoing terminal.
  3. Subtract values; more than 0.2 Ω difference signals weak joints. “Measurement … will explain everything in a moment” [Elektroda, elpapiotr, post #12402153]

What paperwork should I keep before filing a complaint?

Keep the loop-impedance report, voltage-logging chart (10-minute average over 24 h), and electrician’s statement locating the fault upstream. Attach photos of damaged devices for compensation [PSE, 2020].

What damage can a loose neutral in a three-phase building cause?

A broken neutral shifts phase voltages up to 400 V. Sensitive electronics, HDMI ports, and SMPS fail quickly—an edge case noted when TV and GPU burned out [Elektroda, sapsapl, post #12813893]

How much should professional testing cost?

Expect around 200 PLN for loop impedance and basic safety checks in Poznań, confirmed by forum pricing [Elektroda, GBW, post #12820939] Complex 24-h loggers add ~150 PLN/day [GUM, 2022].

What is WLZ and why does its state matter?

WLZ (main riser cable) feeds all flats. Age, corrosion, or overloaded conductors lower voltage for everyone. Upgrading to 10 mm² Cu often restores stability and allows higher allotted power [Elektroda, robin161, post #12401752]

Are LED bulbs more sensitive to voltage dips than incandescent ones?

Yes. LEDs start flickering at 3–4 % rms sag, while incandescents visibly dim only beyond 7 % [IEEE, 2015]. Therefore small dips that seem minor for a 100 W bulb may be very noticeable with LEDs.
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