CME Electrical Codes & Standards 2

Question 1

Under NEC Article 230, what is the maximum number of service disconnects permitted for a single-occupancy building?

Accepted Answer

Six

Answer

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?

Accepted Answer

Article 450

Answer

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?

Accepted Answer

Primary protection set at 125% of rated current satisfies the NEC for most cases

Answer

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?

Accepted Answer

30°C

Answer

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?

Accepted Answer

The equipment grounding conductor

Answer

NEC 250.122(B) requires the equipment grounding conductor to be proportionally increased when the OCPD is upsized.

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