NCCER Electrical Level 3 Module 5 'Overcurrent Protection' exam(fully solved)(verified for accuracy)

Worn motor bearings are most to result in a(n)___. continuous overload A high-level short circuit current may exceed ___. 50,000A` Accidental contact between an electrical conductor and a grounded enclosure is called a(n)___. ground fault Most arcing faults begin as ___. ground faults A plug fuse with a hexagonal cap has a maximum amperage rating of ___. 15A Under normal operation and at currents near its ampere rating, a fuse operates as a ___. conductor UL classifies low-voltage fuses as those operating at ___. 600v or less A standard circuit breaker frame size is ___. 100A The interrupting capacity of a circuit breaker is based on its rated ___. voltage A feeder circuit with no motor load has a continuous load of 10A and a noncontinuous load of 5A. The feeder overcurrent protective device should be sized at ___. 17.5A 10A(1.25)+5A=17.5A The full-load current rating of a 300kVA, three-phase transformer operating at 480v is ___. 361A 300kVA(1000) 480v(1.73) = 361 If a circuit breaker has tripped and stays on for a limited time before tripping again after being reset, the problem is least likely to be a(n) ___. ground fault Which of the following is true with regard to fuses? Fuseholder clips that have lost their spring cannot be repaired with pliers; they must be replaced. Which of the following best describes the maximum short circuit current that a fuse or circuit breaker will safely interrupt? AIC A plug fuse is typically used in a ____. branch circuit A 600v fuse can be used in ___. A 240v circuit A type of fuse with a grooved ring in one ferrule is a Type ___. R Each of the following is a basic factor to consider when applying any fuse, except ___. manufacture's brand name For proper coordination, the total clearing time of any downstream protective device must be below a curve representing which percentage of the minimum melting curve of the fuse being applied? 75% The minimum interrupting rating of branch circuit listed fuses is ___. 10,000A The minimum voltage rating of branch circuit fuses is ___. 125v All of the following are classifications of medium-voltage fuses, except____. proportion fuses An explosion fuse is best described as a ___. vented fuse in which the explosion effect of gases produced by the arc and lining of the fuseholder, either alone or aided by a spring, extinguishes the arc The maximum fuse size for a single-element, non-time-delay fuse serving a 10hp, three-phase motor is ____. 100A One characteristic of a dual-element, time-delay fuse is that it ___. provides backup protection if the other protective device fail to operate When a common circuit breaker trips, the handle is in the ___. middle position A 60A circuit breaker has a frame size of __. 100A When circuit breakers are classified as a 100A through 2,000A frames, these numbers are normally referred to as the ___. frame size A feeder circuit with no motor load has a continuous load of 15A and a noncontinuous load of 10A. The feeder overcurrent device should be sized at ___. 28.75A 15(1.25)+10A=28.75A The full-load current rating of a 225kVA, three-phase transformer operating at 240v is ____. 542A 225kVA(1000) 240v(1.73) = 542A The full-load current rating of a 150kVA, three-phase transformer operating at 240v is ___. 362 150kVA(1000) 240v(1.73) = 362 The let-through short circuit current of a 500kVA, 120/208v three-phase transformer is ___. 69,444A A circuit breaker that trips instantly or fails to reset is most likely the result of ___. a short circuit A short circuit current is one that flows outside the normal conducting paths and may be either line-to-line or ____. line-to-ground The AIC rating of a circuit breaker or fuse is the _____. maximum fault current that the breaker will safely interrupt If a fault current exceeds the interrupting rating, what can happen? The protective device can be damaged or destroyed; such current can also cause severe damage to equipment and injure personnel. Name the factors that must be considered when calculating the required interrupting capacity of an overcurrent protective device . overcurrent protective device, total impendence, equipment short circuit current ratings The two most common voltage ratings for low-voltage power distribution fuses are ___. 250v or 600v True or False? The voltage rating of a fuse can be greater than the circuit voltage. True: For example, a 600v fuse can be used in a 240 circuit. True or False? The rating that defines the capacity of a protective device to maintain its integrity when reacting to fault currents is termed its voltage rating. False: its is termed "Interrupting rating" Why is the coordination of protective devices important? They prevent system power outages and/or blackouts caused by overcurrent conditions Class H fuses have an interrupting rating of ____. 10,000A The basic factors that must be considered when applying any fuse include the _____. voltage, continuous current-carrying capacity, Interrupting rating True or False: Current-limiting fuses produce arc voltages that exceed the system voltage. True Circuit breakers are grouped for identification according to given current ranges. Name them. 15A-100A