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.
Highlights
Electricity is dangerous and required proper protection to prevent unwanted voltage from passing through personnel, critical equipment and other nearby metallic objects [1].The security and reliability of the electrical energy infrastructure is of vital importance today more than ever, given the degree to which electric-powered technology has become embedded in all human activities
One of the components involved in power-system protection is the circuit breaker which is responsible for breaking the system when a fault or anomaly occurs in order to protect the electrical equipment [3, 4]
Electrical protection for residential, office and commercial buildings is based on a well- design circuit breaker that will trip or fuses being blown when an overload happens [6, 10].The current state-of-the-art in this field highlights that the traditional circuit breakers are still widely used today for power-system protection, these devices being usually designed to protect against a single power supply grid fault [7]
Summary
Electricity is dangerous and required proper protection to prevent unwanted voltage from passing through personnel, critical equipment and other nearby metallic objects [1].The security and reliability of the electrical energy infrastructure is of vital importance today more than ever, given the degree to which electric-powered technology has become embedded in all human activities. Protecting the electrical power supply system against interruptions due to various faults is researchable [2]. One of the components involved in power-system protection is the circuit breaker which is responsible for breaking the system when a fault or anomaly occurs in order to protect the electrical equipment [3, 4]. Electrical protection for residential, office and commercial buildings is based on a well- design circuit breaker that will trip or fuses being blown when an overload happens [6, 10].The current state-of-the-art in this field highlights that the traditional circuit breakers are still widely used today for power-system protection, these devices being usually designed to protect against a single power supply grid fault [7]. MCCBs are required to trip above rated current [8]
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