In a time-current curve, what does the horizontal axis represent?

In a time-current curve, what does the horizontal axis represent?

• A. Time in Seconds
• B. Current in Amperes
• C. Voltage
• D. Power

Answer: (B)

Time-current curves show how long a protective device takes to trip for a given fault current. The horizontal axis is current in amperes, because you read the current level directly across the bottom and then look up the corresponding trip time along the curve. This arrangement makes the inverse-time behavior easy to see: as current increases, the operating time decreases. Voltage or power aren’t the quantities tracked on this type of curve, since it’s the current level that determines how quickly the device responds.

Time-current curves show how long a protective device takes to trip for a given fault current. The horizontal axis is current in amperes, because you read the current level directly across the bottom and then look up the corresponding trip time along the curve. This arrangement makes the inverse-time behavior easy to see: as current increases, the operating time decreases. Voltage or power aren’t the quantities tracked on this type of curve, since it’s the current level that determines how quickly the device responds.