Electrical Circuits Exam flashcards
What is a single line diagram?
simplified form of a schematic, done in a vertical line
What is the order for JIC/NEMA prints numbering system?
the first digits are the page numbers, the next 2 are the line number, the last digit is the connection on the line.
What are the stages to motor branch protection?
from left to right: short circuit and ground fault protection device, motor overload protection device, thermal protector
What time does it take for a CLASS 10 overload protector to trip?
10 seconds or less, Class 30 is 30 seconds or less etc.
What is most commonly used to start a motor?
A contactor. A contactor is like a relay that is designed for 3-phase motor loads.
What is the purpose of a soft motor starter?
A solid state device thats purpose is to slowly start a motor to decrease the current draw while the motor is accelerating.
What is the way to cause a three-phase motor to reverse?
Interchanging any two leads to a three-phase motor will cause it reverse, the most common way is to switch Line 1 and Line 3, Line 2 stays the same.
What practice must be used when reversing a motor?
Using both mechanical and electrical interlocks, if both contactors are energized at the same time it would cause a short circuit.
What is jogging?
The momentary operation of a motor for the purpose of accomplishing small movements of the driven machine.
What is plugging?
plugging stops a three phase motor quickly by momentarily connecting the motor for reverse rotation while the motor is still running in the forward direction.
What is dynamic braking?
Dynamic breaking is when a running motor is reconnected to act as a generator, quickly stopping the motor and turning the mechanical energy into electrical energy that can be dissipated by resistors.
What are friction brakes?
Used to hold a motor in place when its stopped by using a spring and solenoid, and brake pads etc.
What are the components of a VFD?
A converter, DC Bus, Inverter and control logic
What are Hall effect sensors?
these sensors detect magnets and are typically used for the detection a position of a cylinder.
