CLD Electrical Systems & Lighting Control 3 — Questions and Answers
Question 1: A lighting control system uses astronomical time clock functionality. What is the primary benefit for a façade lighting application?
- It eliminates the need for daylight sensors
- It automatically adjusts ON/OFF times as sunrise and sunset shift seasonally (Correct answer)
- It reduces lamp operating hours by 50%
- It integrates with DALI addressing automatically
Correct answer: It automatically adjusts ON/OFF times as sunrise and sunset shift seasonally
Astronomical time clocks calculate local sunrise and sunset based on GPS coordinates and date, adjusting schedules throughout the year without manual reprogramming.
Question 2: What does 'inrush current' refer to in the context of LED driver specification?
- The steady-state operating current of the LED array
- The brief high-current surge drawn when power is first applied (Correct answer)
- The maximum dimming current at 1% output
- The short-circuit fault current rating
Correct answer: The brief high-current surge drawn when power is first applied
Inrush current is the high transient current drawn by the driver's input capacitors at power-on, which can trip breakers or damage dimmers if not properly rated.
Question 3: In a three-phase 208V wye distribution panel, what is the line-to-line voltage between any two hot conductors?
- 120V
- 208V (Correct answer)
- 240V
- 277V
Correct answer: 208V
In a 120/208V wye system, the line-to-line voltage is 120V × √3 ≈ 208V.
Question 4: Which control protocol transmits data over standard Category cable and supports bidirectional communication for fixture status feedback?
- 0–10V analog
- DMX512
- DALI (Correct answer)
- Lutron Radio Ra2
Correct answer: DALI
DALI is a bidirectional digital protocol that allows controllers to query fixture status, lamp failures, and energy data over standard wiring.
Question 5: A lighting designer reviews a panelboard schedule and notes that circuit breakers are listed as '20A, 1-pole, HACR.' What does HACR indicate?
- The breaker has arc-fault protection
- The breaker is rated for heating, air conditioning, and refrigeration motor loads (Correct answer)
- The breaker includes a ground-fault interrupter
- The breaker is suitable for high-altitude installations
Correct answer: The breaker is rated for heating, air conditioning, and refrigeration motor loads
HACR (Heating, Air Conditioning, Refrigeration) ratings indicate the breaker can tolerate motor startup current spikes without nuisance tripping.
Question 6: What is the recommended maximum voltage drop percentage for branch circuits supplying sensitive LED drivers according to good design practice?
- 1%
- 3% (Correct answer)
- 5%
- 7%
Correct answer: 3%
A maximum 3% voltage drop on branch circuits (and 5% total including feeders) is the commonly accepted guideline to ensure proper driver performance.
Question 7: Which statement correctly describes the difference between a 'scene' and a 'zone' in a lighting control system?
- A zone is a collection of programmed light levels; a scene is a physical circuit grouping
- A scene is a preset combination of levels across multiple zones; a zone is a group of fixtures controlled together (Correct answer)
- Scenes and zones are interchangeable terms
- A zone applies to daylighting only; a scene applies to artificial light
Correct answer: A scene is a preset combination of levels across multiple zones; a zone is a group of fixtures controlled together
A zone is a physical or logical group of fixtures, while a scene is a saved combination of intensity levels across one or more zones recalled as a single command.
CLD Electrical Systems & Lighting Control 3
A lighting control system uses astronomical time clock functionality.
What is the primary benefit for a façade lighting application?