Replacing an electrical outlet usually seems straightforward: remove the old device, connect the conductors, install the new receptacle, and fit the cover plate.
During the final electrical work on an apartment remodeling project in South Korea, however, we encountered a problem that turned a routine outlet replacement into a much more detailed retrofit job.
The new grounded receptacles would not sit flush with the finished wall. No matter how carefully we pushed them into the existing openings, a visible gap remained behind the cover plate.
At first, the steel electrical box appeared to be too shallow. After removing the device and examining the original mounting structure, we found a different cause: the old box-extension hardware and the new receptacle were physically interfering with each other.
Understanding the Existing Wall Structure
The wall contained a steel electrical box embedded inside the structure. In front of the box was an extension fitting commonly called “Kongkaba” (콘카바) on Korean construction sites.
This fitting helps position a switch or receptacle relative to the finished wall surface. After the steel box and extension fitting are installed, plaster, gypsum board, or another finishing material is applied around the opening.
The important detail on this site was that the existing assembly used a switch-type concave ring. It had worked with the original devices, but its shape did not provide enough clearance for the rear mounting structure of the new grounded receptacle.
Existing steel electrical box and switch-type concave ring installed behind the finished wall.
Why the New Grounded Receptacle Would Not Sit Flush
When we tried to install the new grounded duplex receptacle, it stopped before reaching the finished wall surface.
The reason became clear after comparing the existing concave ring with the back of the new receptacle. The ring had raised screw-mounting sections at the top and bottom.
The new receptacle also had metal mounting sections projecting from its rear. As the receptacle was pushed inward, these two structures contacted each other.
Once they touched, the receptacle could not move any farther into the wall. The result was a visible gap between the receptacle plate and the finished surface.
Interference points between the rear mounting sections of the new grounded receptacle (left) and the raised sections of the existing concave ring (right).
The Modification at a Glance
The diagram below shows the solution more clearly than the job-site photographs alone. Only the two interfering raised sections at the top and bottom of the concave ring were removed.
After additional interference on the receptacle itself was removed, the device could move farther inward. Four available holes in the receptacle frame were then used as fastening points.
Illustration of the field modification: two interference points were removed, and four fastening locations were used to secure the receptacle deeper inside the existing assembly.
Why We Did Not Re-Embed the Steel Boxes
One possible solution would have been to remove each existing steel box, open the finished wall, and reinstall the box deeper with components better matched to the new receptacle.
By the time we discovered the problem, however, the apartment finishes were already completed. Re-embedding approximately 25 boxes would have required substantial wall demolition.
There was another site constraint. Construction noise had already caused several complaints from other residents in the building, and additional hammer drilling was no longer practical.
A surface spacer could also have provided additional clearance, but the customer specifically requested that the finished outlets remain flush with the wall for appearance reasons.
Adding a spacer provides extra clearance, but it also increases the distance between the receptacle and the finished wall surface.
Cutting the Two Interference Points
We used an oscillating multi-tool fitted with a metal-cutting blade to remove the raised mounting sections at the top and bottom of the existing concave ring.
The goal was not to remove the entire extension fitting. We removed only the two areas that were preventing the receptacle from moving inward.
This required controlled cutting because existing conductors were located immediately behind the work area. The blade had to be kept away from conductor insulation and other parts of the box assembly.
An oscillating multi-tool with a metal-cutting blade was used to remove the two interfering sections of the existing concave ring.
Modifying and Repositioning the Receptacle
The receptacle itself also had rear metal mounting sections occupying the same space. Those interfering sections were removed so that the device could move farther into the existing opening.
Once the obstruction was eliminated, the difference was immediately noticeable: the receptacle could now move inward until the front of the device aligned much more closely with the finished wall.
Securing the Receptacle at Four Points
After removing the original interference, the receptacle still needed to be firmly secured.
Four available holes in the receptacle frame were used as fastening points. Self-drilling screws were driven through these locations into the existing steel box structure behind the wall.
Using four points helped keep the receptacle stable and properly aligned while allowing the device to remain farther inside the wall opening. After fastening, the receptacle was checked for movement and alignment before the finish plate was installed.
Four available holes in the receptacle frame were used as fastening points for the field modification.
Final Result: A Flush Finish
After the interference points were removed and the receptacles were secured in their new positions, the cover plates finally sat tightly against the finished wall.
There was no longer a noticeable gap or spacer behind the outlet, and the finished appearance matched the customer's request.
Final result: the grounded receptacle is firmly secured and sits flush with the finished wall surface.
What This Retrofit Taught Us
Existing buildings can present problems that are difficult to predict before devices are removed. A replacement receptacle may look compatible from the front, while a few millimeters of hidden metal behind the device can completely change the installation.
In this case, the useful question was not simply, “Is the box deep enough?” It was: “Exactly where is the new device stopping?”
Finding that exact contact point allowed us to solve the problem without reopening all of the finished walls.
Korean Construction Field Terms
1. 콘카바 (Kongkaba) — Box Extension / Concave Ring
Kongkaba (콘카바) is a Korean construction-site term commonly used for a metal or plastic extension fitting installed in front of an embedded electrical box. It helps position a switch or receptacle relative to the finished wall surface.
In this project, a switch-type Kongkaba had been installed behind the existing outlets. Its raised upper and lower mounting sections interfered with the rear structure of the new grounded receptacles.
Safety and Retrofit Context
This article documents a field solution used on an existing finished installation. It is not intended as a universal installation method for every building or electrical system.
New installations should use properly matched electrical boxes, extension fittings, wiring devices, and fastening methods in accordance with applicable local requirements and manufacturer instructions.
Electrical circuits should be de-energized and verified before work begins. Cutting or drilling near concealed conductors can damage insulation and create shock, short-circuit, or fire hazards.
Korean Electrical Construction · Field Experience · Safety · Technical Education
Website: electrickorea.co.kr
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