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Electrical Systems Design & Installation Flashcards

7 cards from real CME practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Electrical Systems Design & Installation flashcards as text

  1. When installing a 1000 kVA, 480-208Y/120V transformer, what minimum clearance must be maintained from combustible material per NEC 450.21(A)?

    Answer: No clearance required if ventilated

    NEC 450.21(A) permits dry-type transformers rated 112.5 kVA or less to be installed with no separation from combustible material if enclosed; larger units require 12 inches or fire-resistant construction.

  2. Per NEC 220.87, what method allows an existing service or feeder to be evaluated for additional load without full load calculation?

    Answer: Measured demand method using 12-month data

    NEC 220.87 permits using the maximum demand data from the previous 12-month period measured at the meter to determine available capacity for new loads.

  3. In a switchboard installation, what is the minimum headroom required in front of the equipment per NEC 110.26(A)(3)?

    Answer: 6.5 feet

    NEC 110.26(A)(3) requires a minimum headroom of 6.5 feet (2.0 m) in front of electrical equipment 600V or less.

  4. A photovoltaic system is connected to a 200A residential service panel. Per NEC 705.12(B)(3), what is the maximum breaker size allowed for the PV interconnection?

    Answer: 40A

    NEC 705.12(B)(3) limits the PV supply breaker to 120% of the bus rating minus the main breaker; for a 200A panel with 200A bus, maximum PV breaker = (200A × 120%) - 200A = 40A.

  5. What is the purpose of an equipment bonding jumper in an electrical system per NEC Article 250?

    Answer: Bond non-current-carrying metal parts to the grounding system

    Equipment bonding jumpers connect non-current-carrying metal parts (conduit, enclosures, equipment frames) to the equipment grounding conductor to ensure fault current can flow safely.

  6. When designing an industrial control panel with multiple 480V motor starters, what NEC article specifically governs the internal wiring and component requirements?

    Answer: Article 409

    NEC Article 409 covers industrial control panels including short-circuit current ratings, wiring methods, and component requirements for motor control centers and industrial panels.

  7. A 3-phase, 4-wire, 208Y/120V panelboard serves a mixed load. Per NEC 408.36, what is the maximum number of overcurrent devices (poles) permitted in a lighting and appliance branch circuit panelboard?

    Answer: 42 poles

    NEC 408.36 limits lighting and appliance branch circuit panelboards to a maximum of 42 overcurrent devices (counting each pole of a multi-pole breaker).