In this episode of “EC&M Tech Talks,” Randy Barnett, a journeyman electrician, inspector, author, trainer, and electrical safety expert, takes a typically dry topic — electrical theory — and reviews the basics that benefit workers in the field. Electrical codes and standards are based on the physical attributes of electricity. Sine waves, RMS meter readings, single- and 3-phase power, and harmonics are examples of electrical need-to-know basics in order to interpret portions of the NEC.
Very basic explanations of voltage, current, and resistance are provided. The generation of the single-phase sine wave is used to show how the multimeter reads RMS values of the sine wave while peak values are significantly higher. The 3-phase sine wave is drawn on the digital white board demonstrating the advantages of 3-phase power. Article 250, Grounding and Bonding, requires minimum impedance to divert voltage surges into the earth and clear ground faults when required.
The most common 3-phase transformer is the delta-wye connection — the primary side of the transformer being delta connected and the secondary being wye-connected. It is important for electrical workers to understand the development of the 480Y/277V and 208Y/120V levels. The term “wye-connected” is used in the National Electrical Code, and workers should understand the terminology to understand the applications.
References to harmonics in Art. 310 of the NEC are noted. The origins of harmonic currents are explained. A power quality analyzer is displayed in the Tech Talk, and Randy explains the problems created, particularly by the third (180 Hz) and fifth (300 Hz) harmonics. Three-phase wye connections and harmonic currents help with understanding the NEC requirements regarding when to consider the neutral a current-carrying conductor.
