Quiz on the Code
Article 450 - Transformers
For a transformer rated 1,000 volts or less with primary-only overcurrent protection (no secondary OCPD), Table 450.3(B) limits the primary protective device to what maximum percentage of the transformer's primary full-load current? [Table 450.5(B)]
115%
125%
175%
250%
When both primary and secondary overcurrent protection are provided on a transformer rated 1,000 volts or less, Table 450.3(B) allows the primary OCPD to be sized up to what percentage of primary full-load current? [Table 450.5(B), Note 1]
125%
150%
200%
250%
Under the "25-foot tap rule," transformer secondary conductors may run without overcurrent protection at their source, provided their length does not exceed____ feet and the secondary conductors shall have an ampacity that is not less than the value of the primary-to-secondary voltage ratio multiplied by one-third of the rating of the OCPD protecting the primary of the transformer. [240.21(C)(6)(1)]
10 ft
15 ft
25 ft
50 ft
Per 450.16, a disconnecting means is required for transformers of any voltage, with one key exception. Which transformers are exempt from this disconnecting means requirement? [450.16]
Dry-type transformers under 15 kVA
Class 2 or Class 3 transformers
Transformers installed in a supervised location
Single-phase transformers under 25 kVA
On the secondary side of a transformer rated 1,000 volts or less, Table 450.5(B) sets the secondary overcurrent protective device (when required) at what percentage of the secondary full-load current? [Table 450.5(B)]
100%
115%
125%
175%
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