The old air-conditioning panel was working, and we did not consider it unsafe. So why remove it?
It was located only about one meter from the main distribution panel and was connected by a 25 mm² 4-core CV power cable. The building operator wanted the separate panel removed, which raised a practical question: could the existing air-conditioning circuits be integrated into the main panel without unnecessarily replacing equipment that was still usable?
This project took place at a fitness center inside a workforce development facility in Gyeonggi-do, South Korea. The objective was not emergency repair, but panel consolidation, cleaner organization, and better use of the available electrical space.
Location: Fitness center in Gyeonggi-do, South Korea
Main breaker: 150 A
Work: Relocation of existing air-conditioning branch breakers
Crew: Two electricians
Working time: Approximately 9:00 a.m. to 10:30 a.m.
1. Why Change a Working Panel?
A separate electrical panel is not automatically a problem. In this case, the existing arrangement had been operating normally, and we did not identify an immediate electrical safety issue simply because the air-conditioning breakers were installed in a separate enclosure.
However, the separate panel occupied additional space and required a short feeder between two panels located very close to each other. The building operator preferred a more consolidated arrangement.
When nearby electrical equipment can be integrated without compromising capacity, protection, accessibility, or maintainability, consolidation can sometimes reduce unnecessary cable routing and make circuit relationships easier to understand during future inspection and maintenance.
Panel consolidation is not automatically better in every installation. Capacity, protection, conductor arrangement, available enclosure space, accessibility, and future maintenance all need to be considered. In this case, the two panels were already close together, so consolidation was a practical option.
2. The Existing A/C Panel Arrangement
The main distribution panel was equipped with a 150 A main breaker. From the load side of this breaker, a 25 mm² 4-core CV power cable ran approximately one meter to a separate air-conditioning panel.
That secondary panel had its own 100 A breaker and supplied two air-conditioning systems.
Each air-conditioning set consisted of:
- 4P 50 A ELB for one outdoor unit
- 2P 20 A ELB for one indoor unit
There were two identical sets, plus two additional 20 A breakers that were retained as spare circuits.
Existing arrangement before modification: a separate A/C panel was installed about one meter from the 150 A main distribution panel and supplied through a 25 mm² 4-core CV cable.
Before and After
150 A Main Breaker → 25 mm² 4-Core CV Cable → Separate 100 A A/C Panel → Individual A/C Branch Breakers
After
150 A Main Breaker → Custom R / S / T / N Busbar Assembly → Existing A/C Branch Breakers
The modification eliminated the short feeder and the separate 100 A panel while retaining the existing air-conditioning branch breakers.
3. Preparing the Custom Busbars
The plan was to install the existing air-conditioning breakers directly below the 150 A main breaker. To do that cleanly, a busbar assembly had to be fabricated to match the dimensions and breaker positions inside the existing panel.
Before the shutdown, we photographed the existing panel and provided its dimensions to an electrical-supply company that we regularly use. A custom busbar assembly suitable for the 150 A main-panel arrangement was fabricated and completed approximately three days after the order was placed.
The assembly provided R, S, T, and N conductors. At this installation, the conductors were identified using brown, black, gray, and blue.
Preparing the busbars in advance was important because the actual shutdown window was short. The more that could be measured, planned, and fabricated before the power was interrupted, the less time the building had to remain without service.
4. Shutdown, Removal, and Reassembly
Work began at approximately 9:00 a.m.. Before dismantling the panel, we contacted the building's disaster-prevention control room and requested that the upstream supply be disconnected from the electrical room.
The modification was therefore carried out as a planned de-energized job.
During dismantling, we removed:
- the existing 25 mm² 4-core CV cable between the two panels,
- the separate 100 A breaker, and
- the separate air-conditioning panel arrangement.
The existing branch breakers were reused. The custom busbar assembly was installed directly below the 150 A main breaker, and the air-conditioning breakers were relocated to both sides of the new busbar arrangement.
The final configuration consisted of two air-conditioning sets. Each set used one 4P 50 A earth-leakage breaker (ELB) for the outdoor unit and one 2P 20 A ELB for the indoor unit. Two additional 20 A breakers remained available as spare circuits.
A significant part of the work was simply organizing the existing conductors and protective-earth connections. There were many wires and grounding connections in a relatively small area, so the final arrangement required careful sorting rather than just moving breakers from one location to another.
Reassembly in progress: the custom busbars were installed below the 150 A main breaker, and the existing A/C branch breakers were relocated into the main panel.
During dismantling, one breaker-terminal bolt refused to loosen. A DeWalt 20 V impact driver eventually released it. Power tools can be useful for removing stubborn hardware, but reassembly is different. I prefer to start critical threaded connections manually whenever possible so I can feel whether the bolt has entered the thread correctly before final tightening.
A damaged thread may appear to be a small mechanical problem, but if a replacement breaker, terminal, or busbar component is not immediately available, it can stop the entire job.
5. Electrical Checks and Functional Test
After the busbars, breakers, conductors, and protective-earth connections had been reorganized, electrical checks were performed before the system was returned to normal service.
N–PE Voltage
With the upstream supply restored, the measured voltage between neutral and protective earth was approximately 0.6 V.
Two-Terminal N–PE Resistance
A two-terminal measurement between neutral and protective earth indicated approximately 2.2 Ω.
This value is recorded as a field measurement from this installation. It should not be interpreted as the result of a conventional earth-electrode resistance test using a dedicated multi-electrode test method.
Field measurements after reassembly: approximately 0.6 V between neutral and protective earth (left) and 2.2 Ω using a two-terminal resistance measurement between N and PE (right).
Insulation Resistance
The relevant circuits were also checked using a HIOKI insulation resistance tester. All of the circuits tested displayed OF MΩ under the selected test condition.
In practical terms, the measured insulation resistance was above the displayed range of the instrument, and no insulation deterioration was identified during these checks.
Insulation resistance testing after reassembly. The tested A/C circuits displayed OF MΩ on the HIOKI insulation resistance tester under the selected test condition.
A panel modification is not complete simply because the breakers fit and the conductors are connected. Electrical checks should be followed by a functional test before the equipment is returned to normal operation.
After the electrical checks were completed, we informed the building's control room that the panel work was finished. Power was restored, and the air-conditioning equipment was operated through the building's automatic control system.
Both air-conditioning sets operated normally. Operating current was not measured during this visit, so the final operational verification was limited to confirming that the air-conditioning systems functioned normally after the modification.
6. What Actually Keeps a 90-Minute Job on Schedule
This panel modification was completed by two electricians in about 90 minutes. That was possible because the busbars had been fabricated before the shutdown, the existing breakers had already been identified for reuse, and the power interruption had been coordinated with the building control room.
But during the job, one stubborn terminal bolt was enough to remind us how easily that schedule could have changed.
Large components such as breakers, cables, and busbars naturally receive most of the attention in electrical work. In the field, however, a damaged thread, a seized bolt, or a poorly seated terminal can stop the entire job when a replacement part is not immediately available.
That is why an impact driver can be the right tool when removing stubborn hardware, while careful manual engagement is often the better starting point during reassembly.
The previous air-conditioning panel was not removed because it had failed or because we considered it dangerous. It was reorganized because the building operator wanted a more consolidated arrangement, and the existing equipment allowed that change to be made without unnecessary replacement.
Good electrical work depends not only on the design of the circuit, but also on how carefully every connection is put back together.
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