Design Of Distribution Board Unit For A Business Focus

Abstract

This research focus on adequate sizing of miniature circuit breakers (MCBs) and Molded Case Circuit Breaker (MCCB) of distribution board unit for a business center/focus. The aim of this research is to overcome the tripping and burning of connected loads in the study area. The load survey of the business center was carried out and the current rating of the associated equipment used were computed, using the data obtained from the name plate of the equipment. The rated values of the existing MCBs and MCCB were compared with the recommended values obtained from international codes in order to determine the inadequacy of the existing ones in term of protection for the connected load. The result obtained shows that 11% of the load are adequately protected against over current, 6% of the existing load is under-rated while 83% of the load were not over current protected in the existing DB.  Re-design the DB protective devices was carried out in accordance with the international codes to avoid tripping and frequent burning of loads. The number of MCBs resigned is 22.5 single phase MCBs. 23 single phase DB are not readily available, three phase, 8-Way DB is recommended with 25% future expansion. The voltage drop for the cable between the MCCB and the supply source is lesser (0.4%) than 3% recommended by NEC. 100% of the load are protected in the new design hence protection for all the connected loads against overcurrent damage thus removing tripping and burning of many connected loads in the studied area   Equation to size DB is proposed in this work. Overcurrent protective device (CB) must conform to international standard of 1.25 multiplying factor in order to adequately protect the intending load. This is necessary to reduce cost of maintenance and or otherwise procurement of new one. It is also necessary to avoid disruption of work or service.