Transformers Level II Lesson 4: Understanding Transformer Overcurrent Protection (22 Questions; Third Year) – Qs & As

Transformers Level II Lesson 4: Understanding Transformer Overcurrent Protection (22 Questions; Third Year) – Qs & As The National Electrical Code® (NEC) requirements found in Section 450.3 are for the protection of ? . - Correct Answer The windings of the transformer only Where primary-only protection for transformers is provided with rated currents of nine amperes or more, the basic rule requires that each transformer rated 1,000 volts, nominal, or less be protected by an individual overcurrent protective device on the primary side, rated or set at not more than ? of the rated transformer primary current. - Correct Answer 125%. Table 450.3(B) For an installation with a 25-kVA, 3-phase transformer, a 440-volt primary, and a 120-volt secondary, calculate the maximum overcurrent protection value (not the standard fuse or circuit breaker rating) using the protection method for primary-only protection. (Round the final answer to two decimal places.) - Correct Answer 41.05 A An installation consists of a 30-kVA, 3-phase transformer, a 480-volt primary, and a 240-volt secondary. Calculate the largest standard size circuit breaker permitted for primary-only protection to be used without applying Note 1 of Table 450.3(B) Calculate the maximum standard size circuit breaker permitted for primary-only protection using Table 450.3(B) - Correct Answer 45.11 A circuit breaker 50 A circuit breaker An installation consists of a 300-kVA, 3-phase transformer, a 480-volt primary, and a 240-volt secondary.Calculate the maximum overcurrent protection value (not the fuse or circuit breaker rating) using the protection method for primary-only protection. (Round the final answer to two decimal places.) - Correct Answer 451.59 A circuit breaker For the installation in the previous question, calculate the maximum standard size circuit breaker permitted for primary-only protection to be used without application of Table 450.3(B), Note 1. - Correct Answer 450 A circuit breaker For an installation with a 150-kVA, 3-phase transformer, a 480-volt primary, and a 240-volt secondary, calculate the maximum standard size circuit breaker permitted for primary-only protection using Table 450.3(B), Note 1. - Correct Answer 250 A circuit breaker For an installation with a 225-kVA, 3-phase transformer and a 480-volt primary, determine the maximum standard size circuit breaker permitted where the method of primary-only protection is used