What is generally considered the maximum allowable supply voltage variation?

• A. 5%
• B. 10%
• C. 15%
• D. 1%

Answer: (A)

Voltage variation is how much actual supply voltage can differ from its labeled nominal value while still keeping equipment functioning reliably. For most general electrical equipment, the standard maximum variation is plus or minus 5 percent. That means if the nominal voltage is 120 volts, the acceptable range is roughly 114 to 126 volts. This 5% tolerance balances typical grid fluctuations with the need to prevent overheating, misoperation, or premature wear. Wider swings, like 10% or 15%, can cause issues for many devices, while 1% is usually more strict than necessary for standard power systems. So, 5% is the commonly accepted maximum variation.