For the purposes of safety and determining the shock hazard, nominal voltage is defined as the normal electrical system design voltage. This can be determined from what is displayed on nameplates, dataplates, schematics, or single-line diagrams. What does the nominal voltage represent?
• Nominal voltage as a design/reference value, not a measured value • Difference between phase-to-phase, phase-to-neutral, and phase-to-hull ground on AC systems • How equipment nameplates and single-line diagrams usually state system voltage (for example, "480 V", "240 V", etc.)
• When an electrical distribution system is described as, for example, "440 V" or "480 V", what exactly are those two numbers referring to in a three-phase system? • On a typical three-phase shipboard system, is the stated system voltage usually between two phases, or between a phase and neutral/ground? • If you look at common system ratings (e.g., 120/208 V, 240/416 V, 277/480 V), which number is treated as the system or nominal voltage in safety and design discussions?
• Check how three-phase system voltages are conventionally labeled in marine and industrial power (e.g., 120/208 V, 277/480 V). • Verify whether electrical safety standards use phase-to-phase or phase-to-neutral when defining nominal system voltage for shock hazard boundaries. • Confirm which of the four options best matches how the voltage on nameplates and single-line diagrams is typically expressed for a three-phase system.
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