Equipment shall be designed so that it is capable of performing its intended function at ______% of its nameplate voltage.

Equipment shall be designed so that it is capable of performing its intended function at ______% of its nameplate voltage.

• A. 45
• B. 85
• C. 65
• D. 75

Answer: (B)

Equipment is designed to operate reliably even when the supply voltage isn’t exactly at the nameplate value. In real power systems, voltages can dip due to peak loads, long feeders, or transformer regulation, so designers specify a minimum operating voltage to ensure the device still works. The 85% threshold provides a practical margin—enough to tolerate typical voltage sags (about 15%) without causing coils to fail to energize, relays to misoperate, or motors to stall. Choosing a lower minimum would leave equipment more prone to malfunction during voltage dips, while 85% balances reliability with realistic electrical variations. Therefore, 85% is the best and most common specification.

Equipment is designed to operate reliably even when the supply voltage isn’t exactly at the nameplate value. In real power systems, voltages can dip due to peak loads, long feeders, or transformer regulation, so designers specify a minimum operating voltage to ensure the device still works. The 85% threshold provides a practical margin—enough to tolerate typical voltage sags (about 15%) without causing coils to fail to energize, relays to misoperate, or motors to stall. Choosing a lower minimum would leave equipment more prone to malfunction during voltage dips, while 85% balances reliability with realistic electrical variations. Therefore, 85% is the best and most common specification.