Quick Project Summary
This project was carried out in a building in Jung-gu, Seoul, South Korea. Rainwater can collect inside the building's high-voltage cable intake room, so a drainage pump required both a new electrical outlet and a route for its drain hose. Two penetrations were therefore made through an approximately 200mm-thick reinforced concrete exterior wall: one for the electrical conduit and one for the drainage-pump hose. With no usable AC power at the work location, all concrete drilling was completed using a cordless rotary hammer.
1. Site Conditions
This job was carried out in a room where the building's incoming high-voltage cables enter. The room is located beside an exterior landscaped area in Jung-gu, Seoul.
One problem with this location is that rainwater can collect inside the room during heavy rainfall, with no convenient route for the accumulated water to drain away.
A drainage pump was therefore used to remove the accumulated water. For the pump installation, two things were required: a power source for the pump and a route to discharge the water outside.
This meant that two separate penetrations had to be made through the reinforced concrete exterior wall.
- Electrical penetration: For the conduit carrying the new outlet circuit.
- Drainage penetration: For the drainage-pump hose used to discharge collected water outside.
There was another challenge: no usable AC power was available at the work location. All concrete drilling therefore had to be completed with battery-powered equipment.
.jpg "Exterior Area Before Electrical Installation")
2. Checking the Reinforced Concrete Wall
Before drilling, I checked the approximate thickness of the exterior wall. The reinforced concrete section was approximately 200mm thick.
Penetrating a wall of this thickness is not particularly unusual in electrical construction, but the situation becomes more demanding when relatively large holes must be drilled entirely with cordless equipment.
For this job, I used a DeWalt cordless rotary hammer with SDS-Plus concrete drill bits.
Both penetrations needed to be enlarged to approximately 28mm in diameter.
.jpg "Measuring Reinforced Concrete Wall Thickness")
3. Why Two Penetrations Were Needed
The two holes had different purposes.
The first penetration was for the electrical conduit carrying the 3-core 2.5mm² CV cable to the new outlet inside the cable room. This outlet provides power for maintenance equipment, including the drainage pump.
The second penetration was for the drainage-pump hose. When water collects inside the cable room, the pump can discharge it through this hose to the exterior.
Both routes had to pass through the same approximately 200mm-thick reinforced concrete exterior wall.
So although the finished installation may appear to involve only a new outlet, the actual work also included creating a drainage route for the room.
4. Why I Use Staged Drilling
Instead of starting immediately with a 28mm concrete bit, I enlarged each penetration in three stages:
14mm → 22mm → 28mm
This is a practical method I often use when making relatively large penetrations with a cordless rotary hammer.
Lower Initial Load on the Tool
Starting with a smaller bit makes the initial penetration easier and places less load on the cordless rotary hammer than beginning immediately with the largest bit.
Checking for Rebar or Other Obstructions
Reinforced concrete contains reinforcing steel, and there is always a possibility of encountering rebar or another obstruction along the planned route.
If I start with a 28mm bit and drill halfway through a 200mm wall before encountering an obstruction, a considerable amount of drilling time and battery capacity may already have been used.
A 14mm pilot hole is much easier to drill. If an obstruction is encountered at this stage, I can stop and reassess the penetration location before much time or battery capacity has been lost.
Once the 14mm pilot hole passes through successfully, I enlarge it with the 22mm bit and then finish the opening with the 28mm bit.
This is not a mandatory drilling sequence. It is simply a practical technique that works well for me when using battery-powered equipment on site.
Photo 3: 14mm, 22mm, and 28mm SDS-Plus concrete bits used for staged drilling.
5. Drilling Without Site AC Power
Two approximately 28mm-diameter penetrations were made through the approximately 200mm reinforced concrete wall.
Because no usable AC power was available at the work location, the entire drilling process was completed with the cordless rotary hammer.
For this work, I used fully charged 18V-class 5.0Ah lithium-ion batteries.
Actual Field Result:
Three full 5.0Ah battery packs were depleted, and part of a fourth battery was required to complete the two penetrations.
This is not a manufacturer specification or a laboratory performance test. It is simply the actual battery consumption I experienced during this particular job.
Actual battery consumption can vary significantly depending on concrete strength, aggregate, reinforcement, drill-bit condition, rotary-hammer condition, drilling pressure, battery condition, and temperature.
Still, it provides a useful real-world reference for electricians who may need to perform similar concrete drilling work where AC power is unavailable.
.jpg "Cordless Rotary Hammer and Batteries")
Photo 4: DeWalt cordless rotary hammer and 18V 5.0Ah battery packs used during the concrete drilling work.
6. Drilling With Rainwater in Mind
Because the purpose of this work was partly related to water accumulation, I also considered the possibility of rainwater entering through the new wall penetrations.
When drilling from the outside toward the inside, I do not make the penetration perfectly horizontal.
Instead, I drill with a slight upward slope toward the interior. This means that the interior end of the penetration is slightly higher than the exterior opening.
The idea is simple. If rainwater reaches the exterior opening, the slope makes it more difficult for water to travel through the penetration toward the inside of the building.
After the conduit and drainage hose are installed, the space around the wall penetrations is sealed with silicone or another suitable sealing material.
The slope itself is not a substitute for proper sealing. It is simply an additional practical detail I use to reduce the possibility of rainwater entering through an exterior-wall penetration.
Photo 5: Two completed penetrations through the reinforced concrete wall — one for the electrical conduit and one for the drainage-pump hose.
7. Installing the CV Cable and Flexible Conduit
For the new outlet circuit, I used 3-core 2.5mm² CV cable.
The cable was routed inside black weather-resistant flexible conduit through the outdoor section.
The flexible conduit provided additional protection for the cable and made it easier to route the circuit along the existing building structure and landscaped area.
The conduit passed through one of the newly drilled penetrations and entered the cable room.
The other penetration was reserved for the drainage-pump hose.
After the conduit and hose were installed, the wall penetrations were sealed to help reduce the possibility of moisture entering the building.
.jpg "Outdoor Flexible Conduit for CV Cable")
8. Stripping CV Cable With a Knipex Tool
One tool I particularly like for this type of work is a Knipex cable stripping tool.
The outer sheath of CV cable can be removed with a utility knife, but this requires care because cutting too deeply can damage the insulation of the conductors underneath.
With a dedicated cable stripper, the outer sheath can be removed quickly and cleanly.
For electricians who regularly work with CV cable, this kind of tool can save a surprising amount of time during cable preparation and termination.
It is one of those small tools that may not look especially important, but becomes very useful once you start using it regularly on real job sites.
Photo 7: Removing the outer sheath of the 3-core CV cable with a Knipex cable stripping tool.
9. Protective Conductor Identification
The 3-core CV cable used for this installation did not contain a dedicated green/yellow core.
For this circuit, one conductor was assigned as the protective conductor.
At the termination point, that conductor was clearly identified using green/yellow marking tape.
This makes the conductor's function easier to recognize during future inspection or maintenance.
The important point is that the original core color itself should not be interpreted as the protective-conductor color. The green/yellow identification at the termination indicates the function assigned to that conductor in this installation.
10. Installing the Earth-Leakage Circuit Breaker
At the supply side, I installed a 2-pole 20A earth-leakage circuit breaker with 30mA residual-current sensitivity inside a separate protective enclosure.
Incoming and outgoing cables entered through fittings at the bottom of the enclosure.
The protective conductor was also connected to the grounding point inside the enclosure.
Because this circuit supplies an outlet in a room where water may accumulate, earth-leakage protection is an important part of the installation.
.jpg "ELCB Internal Wiring")
11. Installing the Covered Outlet
A covered double outlet was installed inside the cable room.
The CV cable entered through the protective flexible conduit, and the line, neutral, and protective conductor were connected to the receptacle.
The new outlet provides a convenient power source for maintenance equipment, including the drainage pump used when water collects inside the room.
When looking only at the finished outlet, the installation may appear relatively simple. However, much of the actual work happened before the final connection was made.
- Checking the approximately 200mm-thick reinforced concrete wall
- Drilling two separate wall penetrations
- Using 14mm → 22mm → 28mm staged drilling
- Managing cordless-tool battery capacity
- Creating a route for the drainage-pump hose
- Routing and protecting the CV cable
- Installing flexible conduit
- Sealing the exterior-wall penetrations
- Identifying the protective conductor
- Installing earth-leakage protection
- Completing the final outlet connection
.jpg "Covered Double Outlet Installation")
Practical Notes From This Job
The most useful part of this installation was not simply adding an outlet. It was solving several practical problems at the same time.
Water could collect inside the cable room, so the drainage pump needed both electrical power and a route to discharge the water outside.
That required two separate penetrations through an approximately 200mm-thick reinforced concrete exterior wall. At the same time, there was no usable AC power available for the drilling work.
Starting with a smaller pilot hole reduced unnecessary load on the cordless rotary hammer and made the initial drilling easier to control.
Progressively enlarging the penetration also reduced the amount of time and battery capacity that could be lost if reinforcement or another obstruction was encountered during the initial drilling stage.
Giving the exterior-wall penetrations a slight upward slope toward the interior, followed by proper sealing around the conduit and hose, helped reduce the possibility of rainwater traveling into the building.
Using flexible conduit provided additional protection for the electrical cable, while the second penetration provided a dedicated route for the drainage-pump hose.
None of these individual tasks were particularly complicated. But on a real job site, small practical decisions like these often determine whether the entire installation works smoothly.
Final Thoughts
At first glance, this may look like a simple outlet installation.
In reality, the job was also about solving a drainage problem inside a high-voltage cable intake room.
The drainage pump needed power, the drain hose needed a route to the exterior, and both routes had to pass through approximately 200mm of reinforced concrete.
The work therefore involved concrete drilling, cordless-tool battery management, cable routing, flexible conduit installation, a drainage-hose penetration, wall sealing, protective-conductor identification, earth-leakage protection, and final electrical termination.
This is one reason I like documenting actual electrical construction work.
The finished installation often looks simple, but the interesting part is everything that happened before the cover was closed.
Real construction sites rarely follow perfect textbook conditions.
Electricians have to understand the basic principles, inspect the conditions in front of them, and choose a practical method that works safely and reliably.
This is how the job was actually carried out on a building site in Seoul, South Korea.
Document ID: EK Construction #002
Published: August 7, 2026
Publisher: Electric Korea — Real Electrical Construction & Field Experience from South Korea
Written by: Foreman Hong | Electric Korea
Website: electrickorea.co.kr
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