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Renovating Block of Flats with Big Plate from '92: Electrical Wiring and Surface-Mounted Box

paulex80 34713 46
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How should I approach renovating the electrical wiring in a 1992 large-panel apartment when the old wiring route is unknown and only one surface-mounted box is visible?

You should not start by tearing out wires or forging random grooves; first have an electrician inspect the apartment on site and identify what type of large-panel system it is and where the existing wiring actually runs [#16030220][#16032043] In large-panel buildings, the cables may be in factory-made ducts, in expansion joints, or in old routes hidden behind plaster, and the box locations can differ from one building type to another [#16030283] Replacement is possible, but it is difficult and must be planned around the slab’s construction, because you need to know where the slab is stressed and where it is compressed before making holes or chases [#16030283][#16032043] Do not assume you can simply chase concrete panels with an SDS; one reply explicitly warns that forging grooves in concrete slabs is not an option [#16030807] If you want recessed wiring, the safe path is to have the routes and box positions designed first, then only prepare the work that the electrician approves [#16029463][#16032043]
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  • #31 16031404
    Łukasz-O
    Admin of electroenergetics
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    The marker?
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  • #32 16031408
    paulex80
    Level 12  
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    Thank you very much for such a lively interest in the topic, I'm tentatively scheduled with an electrician to check this installation, as I get new information I'll be sure to share it. From your descriptions, it seems that various wonders of technology can be expected :-D .
  • #33 16031421
    robokop
    VIP Meritorious for electroda.pl
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    I have a colleague who toils in the renovation of apartments, sometimes he needed help, as it was necessary to smoothly get away with forging - did not hit the apartment without plaster on a large slab - without a problem it was possible to lay the new installation in the furrows formed after tearing out the old one. Plaster was used to compensate for imperfections in the slabs themselves. What you write about, i.e. furrows and technological holes, the old specialists from Elektromontaż mentioned that they met at the German only.
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  • #34 16031455
    Łukasz-O
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    After all, I showed these furrows in the photos. They were at the Poles in Warsaw :)
    The furrows were not in the hollowcore panels.

    As for this lack of plaster, or this emulsion is not quite true. There was the usual putty and mostly on the ceiling. Mostly, however, there was plaster.
  • #35 16031479
    Brivido
    Level 34  
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    Łukasz-O wrote:
    I have shown these furrows in the photos. They were at the Poles in Warsaw :)
    The furrows were not in the hollow core slabs

    Are you talking about one slab or the whole building?
    In that apartment what I gave above the photo with the floor, there were factory vertical furrows and holes for boxes under the ceiling and around the switch. And the adjacent wall was with channels in the middle.
  • #36 16031564
    Łukasz-O
    Admin of electroenergetics
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    Brivido wrote:

    Are you talking about one panel or the whole building?
    In that apartment what I gave above the photo with the floor, there were factory vertical grooves and holes for boxes under the ceiling and near the switch. And the adjacent wall was with channels in the middle.

    I don't understand a bit.
    I meant that in the slabs (not the whole block :) ) with holes there were no furrows, at least I did not encounter.
  • #37 16031727
    popiol667
    Level 18  
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    Quote:
    If we are talking about a large slab, conduits for wires were made at the slab manufacturing stage, as were holes for fixture boxes. Mounting furrows only in some places where partitions were made of pro-monta blocks. There is no plaster to speak of, only the joints of the boards were covered with it.
    Otherwise - it was not a great board.


    That is, that I do not live in a large slab, because I have plaster on the walls? They will be surprised at the cooperative...

    I live in a "big slab". - The partition walls are made of "hole" brick, no installation furrows, 1cm to 1.5cm of plaster on the ceiling in which the lighting wires are laid. The entire aluminum installation was plugged or, if you prefer, on the brick or slab abandoned lime plaster.

    Without any problem it was possible to make furrows in the partition walls, ceiling.

    Of course, we are talking about "cutting" plaster, not furrows "big slab".
  • #38 16031732
    elpapiotr
    Electrician specialist
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    After all, there were plenty of varieties of great plate .
  • #39 16032015
    marek-1983
    Level 17  
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    opornik7 wrote:


    CYRUS2 wrote:
    2. Or forge furrows with an SDS.



    There is no option for forging in concrete slabs. End. Period.


    Why ? That a little concrete will crumble ? It is not possible to cut the bars that sit there.
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  • #40 16032033
    Brivido
    Level 34  
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    Every person is a different interpretation of the violation of the building structure.
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  • #41 16032039
    kkas12
    Level 43  
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    Rods with rods and forging with forging
    First cut the furrow and only then possibly forge if you do not have a furrowing machine.
  • #42 16032043
    TWK
    Electrician specialist
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    I had the opportunity to participate in April in a training course on large slab: http://maz.piib.org.pl/index.php/materialy-sz...-swietle-pb-i-przepisow-wykonawczych?start=20 In addition to the presenter there spoke a gentleman from ITB, whose name I can not remember, professionally engaged in the study of large slab buildings. I asked him quite thoroughly about ways to replace installations in large slab. It is not impossible, but difficult. I regret that his statements are not in the materials from the training, because he very matter-of-factly answered the question of where to make what furrows, what holes, etc. You certainly can't do it "on the spur of the moment", you need to know how these boards work and which way and where to run the wires.

    marek-1983 wrote:
    Why ? That a little concrete will crumble ? It can not be cut bars that sit there.
    You need to know exactly where the slab is in tension and where it is in compression and which way it works. And how does the colleague want to make the holes for the fixture boxes?
  • #43 16032042
    Strumien swiadomosci swia
    Level 43  
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    And from there , I heard a guy forging a metal doorframe and you could hear 6 staircases away forging, so it carries on the concrete.

    And in general, these blocks will one day begin to collapse in the bad sense of the word, so let's not tempt fate.
  • #44 16032403
    xray81
    Level 22  
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    Gentlemen it is a pity to argue, the varieties of great slab as mentioned by Luke-O were many. I myself live in a large slab from 1987 and the slabs have factory ducts for the wires and rather most goes in these ducts. In a block of flats built a few years later where the installation was laid by my friend, the wires are laid on the ground without forging channels because, as he said, they were in a hurry because they were wound up most of the time.
  • #45 16032595
    technikabasenowa
    Level 33  
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    Strumien swiadomosci swia wrote:
    And from there , I heard a guy forging a metal doorframe and you could hear 6 staircases away forging, so it carries on the concrete.

    And in general, these blocks will one day begin to collapse in the bad sense of the word, so let's not tempt fate.



    But there is a difference between forging a doorframe, which anyway mustache in the wall, and forging furrows for how many mb - not to mention forging holes for the can :cry: .
  • #46 16032656
    Strumien swiadomosci swia
    Level 43  
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    You know the metal door frame, it was poured concrete or something to the wall, a massacre.

    Well, it's a good thing it wasn't me who forged the neighbors probably the seals fell out.
  • #47 16033122
    marek-1983
    Level 17  
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    xray81 wrote:
    Gentlemen it's a shame to argue, the varieties of great slab as Luke-O mentioned were many. I myself live in a 1987 big slab and the slabs have factory ducts for the wires and rather most of it goes in those ducts. In the block of flats built a few years later where the installation was laid by my colleague, the wires are laid on the ground without forging channels because, as he said, they were in a hurry because most of the time they were wound up.


    No no it's not that to this day that's how installations are done. It's all about what the customer wants. Recently I had the opportunity to perform such an installation and because the walls and ceilings were to be left untouched or only cleaned of lumps and possibly pozalepanych holes after rods from formwork. And all the cables of the ceiling even to the switches that went in PVC tubes to a given height sockets from the floor in trays also to a given height.

Topic summary

✨ The discussion revolves around renovating a property in a block of flats built in 1992, focusing on electrical wiring and the presence of a surface-mounted electrical box. The original poster seeks advice on whether to remove old wiring and how to proceed with the installation, given a tight budget. Responses suggest hiring a qualified electrician for installation while performing other tasks like painting and tiling. Participants discuss the challenges of working with large concrete slabs, noting that wiring may be embedded in plaster or screed, and emphasize the importance of assessing the site before proceeding. Various methods for running electrical installations in such structures are debated, including the use of factory-made conduits and the potential for creating furrows for new wiring. The conversation highlights the complexity of electrical work in older buildings and the necessity of professional guidance.
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FAQ

TL;DR: About 70 % of Polish flats built before 1995 still carry aluminium wiring [GUS, 2023]; “remodelling is difficult but not impossible” [Elektroda, Łukasz-O, post #16030283] Locate factory ducts, avoid random chiselling, and budget for pro help.

Why it matters: Incorrect chasing can weaken a load-bearing slab and void insurance.

Quick Facts

• Wall thickness in large-slab buildings: 14–24 cm, concrete grade B25 [ITB, 2016] • Safe chase depth in non-load-bearing wall: ≤ ⅓ thickness, never across reinforcement [PN-EN 1996-1-1] • Re-wiring cost (Poland, 2024): approx. 120–200 PLN /m² including materials [Murator, 2024] • Aluminium resistivity is 1.6× higher than copper (2.82 µΩ cm vs 1.68 µΩ cm) [IEC 60228] • Colour code: PE = yellow/green, N = blue; other cores must be re-marked at both ends [LVD 2014/35/EU]

Can I chisel grooves in a large-slab wall for new cables?

Only in non-load-bearing partitions and to a depth under one-third the wall thickness [PN-EN 1996-1-1]. Cutting reinforcement bars can lower capacity by up to 15 % [ITB, 2018]. Several forum experts warn that forging main slabs is banned [Elektroda, opornik7, post #16030807]

Where do the original wires usually run in 1990–1992 slabs?

Factory PVC ducts cast in the slabs carry vertical risers; baseboard channels feed sockets; ceiling lights often share the neighbour’s screed above [Elektroda, retrofood, #16029559; xray81, #16032403].

Is there plaster on large-slab walls?

Most walls have only joint putty, yet many 1980s blocks received a 5–15 mm lime-gypsum skim that hides cables [Elektroda, mawerix123, #16029536; Brivido, #16031126]. Check with a detector before cutting.

How much should I budget to re-wire a 20 m² flat?

Expect 2 400–4 000 PLN for labour and materials (120–200 PLN /m²) [Murator, 2024]. One electrician quoted 500 PLN just for design guidance [Elektroda, pol102, post #16030220]

Is it legal to leave new cables on the surface?

Yes, Polish HD 60364 allows surface trunking if IP > 20 and cables are halogen-free in escape routes [PN-HD 60364, 2022]. It avoids structural risk but affects aesthetics.

Which tools cut channels in concrete safely?

  1. Wall chaser with two diamond blades and vacuum. 2. SDS-plus drill for round boxes. 3. End with hand chisel. Avoid angle-grinders without dust removal [Elektroda, CYRUS2, post #16030467]

Can I reroute ceiling light wiring without touching the neighbour’s floor?

Use expansion joints between slabs: pull new NYM-J cable through with fishtape, then seal with fire-rated foam [Elektroda, Łukasz-O, post #16030283]

What happens if I accidentally cut rebar?

Structural engineers note possible 10–15 % loss of wall load capacity and mandatory certification tests [ITB, 2018]. Insurance may refuse claims after unapproved structural changes.

How do I mark neutral when 4-core cable lacks blue?

Wrap both ends of the spare grey core with blue heat-shrink or tape; regulation requires permanent colour identification [LVD 2014/35/EU; Elektroda, Łukasz-O, #16031381].

How-To: prepare for an electrician’s site visit (3 steps)

  1. Photograph every socket, switch, and visible conduit. 2. Sketch desired new points on a 1:50 plan. 3. Clear 1 m access around walls and supply the building’s structural drawings. “Good prep cuts on-site time by 30 %” [Elektroda, pol102, post #16030220]

Which standard defines wire colours in Poland?

Colour codes follow PN-HD 308 S3; PE is yellow/green, N blue, phases any other colour [PN-HD 308, 2017].

Should I DIY or hire a licenced electrician?

DIY painting is safe, but wiring must meet PN-HD 60364 and may require D+E licence for meter seal breaking. Forum experts repeatedly advise hiring a pro [Elektroda, retrofood, post #16029245]

How can I locate hidden junction boxes under paint?

Scan walls with an AC voltage detector, then thermal camera; junctions often sit 30 cm below ceiling or above switches [Elektroda, elpapiotr, post #16030820] Mark findings before plaster removal.
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