The information on low voltage interruption was obtained from SESB database called Trouble Call System (TCS) and LGBnet. Trouble Call System store the breakdown information from complain consumer who called in. LGBnet is a database system which store information on interruption duration, frequency, no of affected consumer and reliability index such as SAIDI and SAIFI.

Major cause of interruption on low voltage distribution systems is over-current from illegal connection. Short circuit or fault on overhead line also contributes to low voltage interruption. Both of the cases led to blown fuse at a feeder pillar located in a secondary distribution substation hence causes power outage to surrounding consumer.

Breakdown for May 2009 at SESB Tawau was analyzed and Tepekong Cina Substation was highlighted due to its frequent breakdown involving fuse blow. After investigation, illegal connection from squatter housing causes over-current or high load to the LV systems and blown the fuse use for transformer protection. A single illegal connection can rate up to 200A and brings around 50 kW of load to the system.


From interview and observation, it’s not just tree branches that causes short circuit and fault but also causes by illegal connection. Double line short occurs when insulation of the illegal wire has torn. Multiple tapping of illegal connection on different phases lead to phase-to-phase short circuit due to incompetent wiring. Illegal wires were also laid crosses drain and puddle.

Unbalance load on a three phase system can occurred when loads connected to each phase were uneven. High load on a single phase cause fuse blow. It can be avoided if load were connected evenly on the three phases. Unbalance load occurred because of multiple tapping of connection to a single phase and there is no load monitoring system for LV distribution systems. Responsible technician for new service connection tapped random phases whichever they think suitable.