PLC (Chapter 1)

Question 1

What does MCC stand for ?

Answer 1

A motor control center (MCC) is an assembly of one or more enclosed sections having a common power bus and principally containing motor control units. Motor control centers are in modern practice a factory assembly of several motor starters.

Question 2

What does WD stand for?

Answer 2

Wiring Diagram

Question 3

What does I.A stand for?

Answer 3

Inrush current, input surge current or switch-on surge is the maximum, instantaneous input current drawn by an electrical device when first turned on. Alternating current electric motors and transformers may draw several times their normal full-load current when first energized, for a few cycles of the input waveform

Question 4

What does OL relays stand for?

Answer 4

Overload relays protect a motor by sensing the current going to the motor. Many of these use small heaters, often bi-metallic elements that bend when warmed by current to the motor. When current is too high for too long, heaters open the relay contacts carrying current to the coil of the contactor.

it is usually in Amps

Question 5

what is PAC?

Answer 5

Programmable automation controllers.

Question 6

What does PCS stands for?

Answer 6

Process Controls Systems

Question 7

What does PNC stands for?

Answer 7

Process Control Narrative

Question 8

What does (P and IDs) stand for?

Answer 8

Process and Instrumentation Diagrams

Question 9

What does (P and IS) Stand for?

Answer 9

Process and instrumentation schematic

Question 10

What is a cycles of the input waveform and the time of I.A ?

Answer 10

60 Cycles Per Second to Hertz = 60
So at 60Hz means 60 cycles per sec, when thinking about I.A (Inrush current) which is the instantaneous maximum current the electrical device draws when switch turns ON. devices such as transformers and motor could have a higher I.A than their rated but that’s only for few cycles. so @ 60Hz frequency one cycle is 1/60 s. that’s devices are not usually affected but the high I.A.

Question 11

What are the main parts of an over load relay?

Answer 11

1) Contact (open/close)
2) two bi-metallic strip which have a different in the coefficient of thermo-expansion. the one with higher coefficient is the that bents.
3) Heater
4) link bar between the contact and the metallic strip