Electrical Supply Systems and Distribution Flashcards
7 cards from real ECS 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 Supply Systems and Distribution flashcards as text
What is the standard frequency of the electrical supply in the United States?
Answer: 60 Hz
The US electrical supply operates at a standard frequency of 60 Hz, meaning the AC current completes 60 full cycles per second.
In a three-phase 208V/120V Wye system, what voltage would you measure between any two line conductors?
Answer: 208V
In a Wye (star) configured system, the line-to-line voltage is the phase voltage multiplied by the square root of 3 (√3 × 120V ≈ 208V).
What is the purpose of a sub-distribution board (SDB) in a large commercial electrical installation?
Answer: To distribute power locally within a zone, fed from the main distribution board
A sub-distribution board receives its supply from the main distribution board and distributes power to circuits within a specific area or floor of a building, reducing cable runs.
Which type of electrical supply system uses a separate protective earth (PE) conductor and a neutral (N) conductor throughout the installation?
Answer: TN-S system
A TN-S system has separate neutral and protective earth conductors throughout the entire installation, providing the most reliable earth fault protection.
What is the primary advantage of a ring main circuit over a radial circuit for socket outlet distribution?
Answer: It provides two paths for current, allowing smaller cable sizes for the same total load
A ring main circuit provides two current paths from the distribution board to any outlet, meaning each path carries approximately half the total current, allowing smaller cable sizes.
What does 'diversity' mean in the context of electrical load calculations for a distribution system?
Answer: The assumption that not all connected loads will operate simultaneously at full load
Diversity in electrical loading accounts for the fact that not all connected appliances and circuits will be in use simultaneously at their maximum rated load, allowing smaller supply capacity.
What is the purpose of a busbar in an electrical distribution panel?
Answer: To provide a common connection point for multiple circuit conductors within the panel
A busbar is a rigid metallic conductor within a distribution panel that provides a common point from which multiple circuits can be connected to the supply.