Exam 18: Short-Circuit Calculations and Coordination of Overcurrent Protective Devices

When determining the f factor, N represents ____.

____ power systems are power systems that are generally installed in vital infrastructure facilities that, if destroyed or incapacitated, would disrupt national security, the economy, public health or safety, and where enhanced electrical infrastructure for continuity of operation has been deemed necessary by governmental authority.

A simple method of determining the available short-circuit currents (also referred to as fault current)at various distances from a given location is the ____ method.

The amount of short-circuit current from a motor is equal approximately to the starting (____)current for each motor.

The amount of available short-circuit current decreases as the ____ from the transformer increases.

A situation known as ____ occurs when a fault on a branch circuit opens not only the branch-circuit overcurrent device but also the feeder overcurrent device.

​The NEC includes a requirement that the ____ short-circuit current available at the service be field marked at or on the service equipment.

To meet the requirements of NEC 110.9 and 110.10, it is absolutely necessary to determine the available fault currents at various points on the electrical system. If a ____ study is not done, the selection of overcurrent devices may be in error, resulting in a hazard to life and property.

The value of the square root of three (____)is used frequently in 3-phase calculations.

What is the approximate line-to-ground arcing fault value on a 480/277-volt system where the line-line-line fault current has been calculated to be 30,000 amperes?

What is the importance of selective coordination? What guidelines cover it?

How can you create a selective system using circuit breakers?

How can you create a selective system using fuses?

​Under what conditions are series-rated systems most often installed?

____ can prevent the occurrence of single phasing.

The actual impedance value on a UL-listed 25-kilovolt-ampere or larger transformer can vary plus or minus ____ percent from the transformer's marked impedance.

To obtain the approximate short-circuit current values when two hot conductors of a 3-phase system are shorted together, use ____ percent of the 3-phase current value.

What is the intent of NEC 110.9 and 110.10 ?

If non-series-rated overcurrent devices (standard molded-case circuit breakers)are to be installed in the main switchboard, breakers with adequate ____ must be installed in the panelboards.

The transformer multiplier M₂ is calculated using the formula ____.