Master Electrician Exam (NEC)General Electrical KnowledgeEasy
A master electrician is designing a lighting circuit for a new commercial office space. The circuit will primarily supply LED luminaires. Which type of transformer is typically used to step down the utility voltage (e.g., 480V) to the building's main distribution voltage (e.g., 208Y/120V) for general-purpose loads like lighting and receptacles?
- ACurrent Transformer
- BIsolation Transformer
- CAutotransformer
- DDistribution Transformer
Show answer & explanationAnswer & explanation
Correct answer: D. Distribution Transformer
Distribution transformers are designed to step down high utility voltages to lower, more usable voltages for general distribution within a building or grid.
Why the other options are wrong
- A. Current transformers are used for current measurement in metering and protection, not voltage transformation.
- B. Isolation transformers are for electrical isolation, not primarily voltage step-down for general distribution.
- C. Autotransformers are used for small voltage changes or motor starting, not large step-downs from utility to building distribution.
Distribution Transformer
A distribution transformer is a step-down transformer used in electrical power distribution systems to lower the primary voltage to a suitable level for consumers.
- Steps down high utility voltage to lower service voltage.
- Commonly found on utility poles or pads.
- Essential for delivering power to residential, commercial, and industrial loads.
Memory trick: Transformers: Isolate, Auto-adjust, Distribute, or Current-sense.