Two field methods for fitting German-style switch boxes into existing Korean concrete walls.
Introduction — The Switch Fits the Design, but Not Necessarily the Wall
The client on this project preferred the clean, simple appearance of German switches. The switches and their dedicated mounting boxes were purchased online for installation in an existing Korean building.
The difficulty was not the appearance of the switch. It was what was already inside the wall.
The walls were finished concrete, with conventional Korean switch boxes already embedded inside. Because the German switches and their dedicated round boxes were not directly compatible with these existing boxes, the installation method had to be decided after opening each location and inspecting what was actually behind the finished surface.
Interestingly, two locations in the same building required two different solutions.
- German switch boxes may not fit conventional Korean wall boxes.
- A sufficiently large existing box may sometimes be retained rather than demolished.
- A smaller existing box may have to be removed and the concrete opening enlarged.
- Compact German boxes are relatively easy to embed, but their limited internal space makes wire management more difficult.
- The practical installation method depends on the actual condition behind the wall.
Completed German rotary and toggle switches installed in a finished Korean concrete wall.
Case 1 — When the Existing Box Is Large Enough
The first location originally had a Korean three-gang switch. After removing the existing switch and carefully removing the thin cement finish around the opening, a relatively large rectangular wall box was exposed.
This turned out to be fortunate. The dedicated German box was shallower than the existing embedded box, so there was no practical reason to remove the entire original box or unnecessarily demolish more concrete. Instead, the existing space was reused.
The existing Korean switch box was exposed after removing the original three-gang switch and the thin surface finish.
Reusing the Existing Opening
The German box was positioned inside the existing opening and initially secured with a screw. A small amount of polyurethane foam was then applied around the box to help hold its position before the surrounding wall surface was restored.
The critical issue here was not the depth of the box. Because the German box was shallower than the existing embedded box, depth was relatively easy to accommodate. The more important task was keeping the new switches at the same height and correctly aligned.
The existing switch locations were approximately 1,200 mm above the floor. A tape measure and spirit level were used to position the new boxes side by side.
The 1,200 mm dimension describes the existing switch height on this particular project. It is not presented as a German switch installation standard.
.jpg "German switch box retrofit inside an existing Korean wall opening")
The shallow German mounting box was positioned within the space of the larger existing Korean wall box.
Restoring the Finished Concrete Wall
Once the electrical box was positioned, the surrounding wall had to be restored.
The wall surface was first rebuilt with plaster or mortar. Wall patching compound was then applied, allowed to harden, and sanded to create a smooth transition between the repaired area and the existing finished wall.
The surface was finally finished with two coats of white water-based paint matching the surrounding wall. These finishing stages were carried out by the respective trades responsible for plastering, surface preparation, sanding, and painting.
The wall was repaired around the newly positioned switch box before final surface finishing.
.jpg "Finished German switch installation after concrete wall restoration")
After patching, sanding and two coats of white water-based paint, the modified opening blends into the finished wall.
Case 2 — When the Existing Box Has to Come Out
The staircase location was different.
Here, the existing wall contained a much smaller single-device box. Unlike the first location, there was not enough room to install the German box within the existing opening. Trying to force the same method used in Case 1 would have made little sense.
The old box was therefore removed.
The smaller existing box at the staircase could not accommodate the new German mounting box.
Enlarging the Concrete Opening
After removing the existing box, the opening was enlarged with a Makita corded demolition hammer.
Only the amount of concrete necessary to accommodate the new box was removed. With the appropriate tool, enlarging the opening was relatively quick. The objective was not to demolish more of the wall than necessary, but simply to create sufficient space for the new mounting box.
Installing the New Box
Once sufficient space had been created, the dedicated round box was positioned in the wall. The surrounding area was then repaired and finished in the same general manner as the first location.
This location ultimately received the two-gang toggle switch.
.jpg "German switch mounting box installed after concrete chiseling")
The dedicated German box was installed after enlarging the original concrete opening.
The completed two-gang German toggle switch at the staircase.
Small Outside, Tight Inside — The Wiring Challenge
The compact size of the German mounting box has an advantage: it does not require a particularly large cavity in the concrete wall.
But the same compact size creates another problem.
There is very little space inside for the conductors.
Leaving the wires with the amount of extra length commonly accommodated in a larger box made it difficult to push the switch mechanism fully into position. The conductors therefore had to be prepared carefully for the available space.
Only the length needed for the actual connection and installation was retained. After termination, the conductors were carefully folded and guided into the box while the switch mechanism was gradually pushed into position.
This required more attention than simply pushing the switch and excess wiring into the box.
.jpg "Limited wiring space inside a compact German switch box")
Limited internal space means conductor length and placement must be managed carefully while inserting the switch mechanism.
The conductors on this project were trimmed to suit the limited available space while retaining the length necessary for termination and installation. Required conductor length, box fill, termination method and applicable electrical requirements must be evaluated for the actual installation.
Existing Wiring
The original three-gang switch contained conductors that were no longer required for the new switching arrangement.
Those unused conductors were insulated and placed back inside the box. Only the two conductors required for the switch being used were connected to the new device.
The exact conductor function is intentionally not generalized here because wiring arrangements and switch configurations can differ between installations.
.jpg "Existing wiring prepared for German switch installation")
The existing conductors were sorted before the new switch mechanism was installed.
Three Switch Types Installed
Three German-style switching devices were installed during this work: one rotary switch, one two-gang toggle switch, and one single-gang toggle switch.
The purpose of this project was not to demonstrate one universal mounting method for these devices. Rather, it shows how different existing wall conditions required different approaches even within the same building.
.jpg "Round mounting boxes for German-style switches")
Examples of the compact round mounting boxes used with the imported German-style switching devices.
Final Checks Before Completion
After each switch was secured and assembled, four basic points were checked.
The switch was checked for movement or looseness, its alignment on the finished wall was visually confirmed, the operating mechanism was tested for smooth movement, and the connected circuit was operated to confirm that the switch functioned correctly.
A clean appearance alone was not considered sufficient if the device was loose or did not operate smoothly.
Final alignment, mechanical stability and switch operation were checked after installation.
Field Verdict — Clean Design, More Difficult Installation
The finished switches have a clean and simple appearance.
From an installer's perspective, however, they are not as straightforward to retrofit into a Korean building as a conventional locally compatible switch.
The existing wall box may not match the imported device. A dedicated mounting box may be required. Concrete may need to be locally removed, and the compact internal space requires careful conductor management.
The switches themselves were also relatively expensive compared with more conventional alternatives used on this project.
For these reasons, this installation should not be viewed as a simple remove-and-replace project for an inexperienced DIYer.
The finished result may look simple.
The work hidden behind the switch is not always simple.
One Product, Two Walls, Two Solutions
The most useful lesson from this project was not a specific hole size or one fixed installation technique.
At the first location, the existing Korean box was large enough to remain in the wall, allowing the smaller German box to be installed within the available space.
At the staircase, the existing single-device box was too small. It was removed, the concrete opening was enlarged, and the new box was installed directly into the modified opening.
There was no reason to demolish a usable existing box simply because another location required demolition. Likewise, there was no reason to force a new box into an opening that was clearly too small.
Inspect the existing condition first, then choose the simpler and safer practical method for that particular wall.
That was the approach used throughout this project. Flexibility and careful inspection are often the most useful tools in retrofit work.
Related Electric Korea Field Record
This concrete-wall retrofit is a follow-up to an earlier Electric Korea field record covering another German switch installation, including adaptation to an existing Korean wall box and installation in a new drywall partition.
How to Install a German Rotary Switch | THPG Installation in South Korea
This article documents a project-specific field installation in South Korea. Existing wall construction, wiring arrangements, box dimensions and applicable electrical requirements may differ by building and jurisdiction.
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