On the night of Sunday, 1 February 2026, four shophouses used as decoration and textile warehouses on Jalan Pajak Raya, Pondok Aren, South Tangerang, caught fire. The head of the South Tangerang fire and rescue service said the fire was suspected to have started from an electrical short circuit in a decoration warehouse of about 500 square metres, then grew quickly because of the amount of wood and styrofoam stored there. Firefighters needed 11 hours to put it out, at 04.20 local time the next morning. Losses were estimated at Rp7 billion, and three people were injured: two residents and one firefighter (Simorangkir, 2026).
The exact cause has not been established. At the time of writing only the firefighters' initial suspicion is available, not an official finding, so we do not speculate about it. What every warehouse, shophouse and factory manager can do is check one basic point in their own installation: whether the load, the protective device and the cable on each circuit are properly matched. This article explains the method and its limits.
The Legal Duty
Indonesia's Minister of Manpower Regulation No. 12 of 2015 on electrical occupational safety and health in the workplace requires employers and managers to implement electrical safety (Article 2) wherever equipment operates above 50 volts AC or 120 volts DC (Article 4). Periodic inspection must take place at least once a year and periodic testing at least once every 5 years (Article 11) (Kementerian Ketenagakerjaan [Kemnaker], 2015a). The amending Regulation No. 33 of 2015 states that inspection and testing are carried out by specialist electrical safety labour inspectors, by the company's appointed electrical safety experts (Ahli K3 bidang Listrik) and/or by experts from a licensed safety service company (PJK3): before handover to the owner, after any change or repair, and periodically (Kemnaker, 2015b).
The Coordination Rule
The low-voltage installation standard IEC 60364-4-43 provides overload protection when two conditions are met: IB ≤ In ≤ IZ and I2 ≤ 1.45 × IZ (International Electrotechnical Commission [IEC], 2023). IB is the circuit design current, In is the rated current or setting of the protective device such as an MCB, MCCB or fuse, IZ is the continuous current-carrying capacity of the cable after correction factors, and I2 is the current that ensures the device operates within its conventional time. The same formulas are used in Indonesian industrial installation studies based on PUIL 2011, the national wiring code (Wiguna et al., 2025).
The logic is simple. In must not be lower than IB, so the device does not trip in normal operation, and In must not exceed IZ, so an overload beyond the cable's capacity is cleared before the insulation overheats. The habit of fitting a larger breaker "so it stops tripping" satisfies the first condition but often breaks the second.
Step by Step
- Collect the single-line diagram and panel schedule. Where none exists, draw one first.
- Calculate IB for each circuit from nameplate data: single phase IB = P / (V × cos φ), three phase IB = P / (√3 × VL × cos φ).
- Record In of each installed device, including the setting of adjustable MCCBs.
- Determine IZ from cable type, size and installation method using ampacity tables with temperature and grouping correction factors.
- Compare the three values, flag circuits that fail, then check I2 from the device's technical data.
- Document the results as part of the periodic inspection.
A Worked Example
The figures below are illustrative and are not data from the fire described above. A 30 kW three-phase machine at 380 V with a power factor of 0.8 has IB = 30,000 / (1.732 × 380 × 0.8) ≈ 57 A. Suppose the circuit is protected by a 100 A MCCB while the cable, after correction factors, has an IZ of only 76 A. The condition 57 ≤ 100 is met, but 100 ≤ 76 fails. Currents between 76 A and 100 A can then flow for long periods while the cable runs beyond its capacity. The fix is to lower the protection to 63 A (57 ≤ 63 ≤ 76) or to replace the cable with one rated at least 100 A, after confirming that the real load is indeed around 57 A.
Such findings are not hypothetical. A study of the installation at a bottled water plant in Bandung found no single-line diagram, cable sizes that did not match actual load currents, MCB and MCCB ratings outside the standard and panels without earthing. On several main loads the installed protective device exceeded the cable's current-carrying capacity and had to be adjusted (Wiguna et al., 2025).
Where It Stops
We see this method as a cheap first screen that needs only nameplate data, a single-line diagram and ampacity tables. It answers one question, however: whether the cable is protected against overload. It does not detect loose connections, ageing insulation, earth leakage or arcing faults, all of which are commonly examined in electrical fire investigations. Equipment added without records also makes the calculation obsolete. The calculation therefore complements, rather than replaces, the periodic inspection and testing required by Regulation 12/2015 (Kemnaker, 2015a).
Factors beyond the cable matter too. In the Pondok Aren fire, officials said wood and styrofoam made the fire spread quickly (Simorangkir, 2026). Combustible goods stacked near panels shorten the time between a first spark and a major fire.
Practical Steps
- Start with the panels that feed storage areas for combustible materials and heating equipment.
- Prohibit replacing an MCB with a higher rating without written approval from the electrical safety expert.
- Keep the space in front of and around panels clear of stored goods.
How Nusa Safety Helps
Nusa Safety helps warehouse, shophouse and factory managers map electrical risk through its Electrical System Assessment, including tracing the single-line diagram and checking protection against cable ratings, and through the Fire and Emergency Safety Audit (FESA). For in-house competence there is electrical safety training; official certification is delivered with licensed PJK3 partners, as Nusa Safety issues only internal training certificates.
This article is general information and not legal or professional advice for any specific case.
References
- International Electrotechnical Commission. (2023). Low-voltage electrical installations - Part 4-43: Protection for safety - Protection against overcurrent (IEC 60364-4-43:2023). https://webstore.iec.ch/en/publication/28432
- Kementerian Ketenagakerjaan Republik Indonesia. (2015a). Peraturan Menteri Ketenagakerjaan Nomor 12 Tahun 2015 tentang Keselamatan dan Kesehatan Kerja Listrik di Tempat Kerja [Minister of Manpower Regulation No. 12 of 2015 on electrical occupational safety and health in the workplace]. Berita Negara Republik Indonesia Tahun 2015 Nomor 540. https://jdih.kemnaker.go.id/peraturan/detail/610/peraturan-menteri-nomor-12-tahun-2015
- Kementerian Ketenagakerjaan Republik Indonesia. (2015b). Peraturan Menteri Ketenagakerjaan Nomor 33 Tahun 2015 tentang Perubahan atas Peraturan Menteri Ketenagakerjaan Nomor 12 Tahun 2015 [Minister of Manpower Regulation No. 33 of 2015 amending Regulation No. 12 of 2015]. Berita Negara Republik Indonesia Tahun 2015 Nomor 1535. https://jdih.kemnaker.go.id/peraturan/detail/1156/peraturan-menteri-nomor-33-tahun-2015
- Simorangkir, H. (2026, February 2). Kebakaran ruko dekorasi dan tekstil di Tangsel diduga akibat korsleting listrik [Decoration and textile shophouse fire in South Tangerang suspected to be caused by a short circuit]. Metrotvnews.com. https://www.metrotvnews.com/read/kELCn7q6-kebakaran-ruko-dekorasi-dan-tekstil-di-tangsel-diduga-akibat-korsleting-listrik
- Wiguna, T. A., Tohir, T., & Hikmat, Y. P. (2025). Analisis dan perancangan ulang instalasi listrik industri di PT. Jayamas Dwi Perkasa berdasarkan Standar Nasional Indonesia (SNI) [Analysis and redesign of an industrial electrical installation based on the Indonesian National Standard]. Prosiding Industrial Research Workshop and National Seminar, 16(1), 34-38. https://doi.org/10.35313/irwns.v16i1.6666
