PROTECTION DEVICES (030204d) Flashcards
When a path of extremely low impedance is created in a circuit, there would be a
Short circuit condition
A fault current is the current that is caused by
A low impedance path to ground
All circuits and electrical systems require protection against an
Overcurrent condition
An overload condition can cause the damage to equipment due to
Excessive heat
What best describes an overload condition
A motor with an excess mechanical load
The continuous rating of an overcurrent device refers to
The current above which the device begins to react
The higher the overload current, the _______ the reaction time
Shorter
A time-limit type circuit breaker will protect a circuit from
Overloads or short circuits
True or false
The interrupting rating of the fuse or circuit breaker is normally in the range of several thousand amperes
True
In motor branch circuits, which circuit characteristics are used when calculating the minimum interrupted capacity for fuses
kVA and percent impedance rating of the supply transformer
One of the factors that determines the maximum short-circuit current in a branch circuit is the
Voltage of the circuit where the fault occurs
The interrupting rating of a circuit protective device applies to all types of _______ _______
Overcurrent devices
True or false
The kVA rating and the percent impedance(IZ%) of the supply transformer, both affect the amount of short circuit current that could flow.
True
True or false
All ungrounded circuit conductors must be disconnected from the motor by disconnecting means .
True
What is the primary purpose of the motor disconnect?
To prove a way of disconnecting the motor from all ungrounded circuit conductors
How many purposes does a fused disconnect have?
2
Line voltage _____ devices, such as thermostats and floats, which is are connected in _____ with the _____ motor circuit switch to control the motor
Pilot
Series
Manual
A thermally responsive overload device is warmed by a heater that is a ____ length of a ____ resistance conductor
Short
Low
What is the full load capacity of a motor?
The highest current set by the manufacturer that the motor can carry without damage
True or false
Except for motor circuits, circuit breakers can generally provide protection against both overload and overcurrent circuit conditions
True
True or false
Most motor branch circuits must have overcurrent protection, overload protection, a controller, and a disconnecting means
True
True or false
Correctly sized standard fuse used as the protective device in a motor circuit will give both overload and overcurrent protection
False
True or false
The ampere rating of a fuse for a motor circuit would depend upon whether it is a standard or time-delay type of device
True
True or false
Fuses and circuit breakers are not to be considered as circuit protective devices
False
