CME Electrical Codes & Standards 2 — Questions and Answers
Question 1: Under NEC Article 230, what is the maximum number of service disconnects permitted for a single-occupancy building?
- Two
- Four
- Six (Correct answer)
- Eight
Correct answer: Six
NEC 230.71 allows a maximum of six disconnecting means for a single set of service-entrance conductors.
Question 2: Which NEC article governs the installation of transformers with a primary voltage over 600V?
- Article 408
- Article 450 (Correct answer)
- Article 480
- Article 490
Correct answer: Article 450
NEC Article 450 covers transformers and transformer vaults, including those rated over 600V.
Question 3: What does the NEC require for overcurrent protection of a 480V, 3-phase, 100 kVA transformer with a secondary of 208Y/120V?
- Primary protection only is always sufficient
- Secondary overcurrent protection must be within 25 feet of the transformer
- Primary protection set at 125% of rated current satisfies the NEC for most cases (Correct answer)
- No overcurrent protection is required for transformers under 112.5 kVA
Correct answer: Primary protection set at 125% of rated current satisfies the NEC for most cases
Per NEC 450.3, primary overcurrent protection set no more than 125% of rated primary current is the standard requirement for most transformers.
Question 4: NEC 310.15 ampacity tables are based on an ambient temperature of how many degrees Celsius?
- 25°C
- 30°C (Correct answer)
- 40°C
- 60°C
Correct answer: 30°C
NEC ampacity tables in 310.15 are based on a 30°C (86°F) ambient temperature unless otherwise noted.
Question 5: According to NEC 250.122, if a feeder circuit's overcurrent device is increased in size to handle a larger load, what must also be increased?
- The neutral conductor
- The equipment grounding conductor (Correct answer)
- The service entrance cable
- The conduit fill percentage
Correct answer: The equipment grounding conductor
NEC 250.122(B) requires the equipment grounding conductor to be proportionally increased when the OCPD is upsized.
Question 6: Under NFPA 70E, what arc flash PPE category requires a minimum arc rating of 40 cal/cm²?
- Category 1
- Category 2
- Category 3
- Category 4 (Correct answer)
Correct answer: Category 4
NFPA 70E Table 130.5(G) assigns PPE Category 4 a minimum arc rating of 40 cal/cm².
Question 7: Which NEC section defines the requirements for working clearances in front of electrical equipment operating at 600V or less?
- NEC 110.26 (Correct answer)
- NEC 230.70
- NEC 408.18
- NEC 240.24
Correct answer: NEC 110.26
NEC 110.26 specifies minimum working clearances, dedicated space, and headroom requirements for equipment up to 1000V.
CME Electrical Codes & Standards 2
Under NEC Article 230, what is the maximum number of service disconnects permitted for a single-occupancy building?