Question 4
- (a) The diagram below illustrates an electrical layout of a one-bedroom apartment. Study it and answer the following questions.
Prepare a legend of the layout in the table below.
(b) State faults that could cause a split-phase motor to hum.
(c) How does a shaded pole motor run?
Observation
4(a): The majority of the candidates excelled in describing the symbols utilized in electrical layout.
4(b): Many candidates were unable to accurately identify the faults that could lead to a split-phase motor humming.
4(c): Many candidates struggled to provide a clear explanation of how a shaded pole motor operates.
The expected answers include:
Expected response:
(a)
S/N |
Symbol |
Description |
Quantity |
Size of cable |
1 |
|
Fan regulator |
3 |
1.0 mm2 / 1.5 mm2 |
2 |
|
Fan |
3 |
1.0 mm2 / 1.5 mm2 |
3 |
|
Twin 13 A socket |
5 |
2.5 mm2 |
4 |
|
13 A socket single |
2 |
2.5 mm2 |
5 |
|
Ceiling mounted fitting (lamp/bulb) |
3 |
1.0 mm2 / 1.5 mm2 |
6 |
|
Wall bracket |
5 |
1.0 mm2/ 1.5 mm2 |
7 |
|
Consumer unit |
1 |
4.0 mm2 |
8 |
|
2 way switch |
2 |
1.0 mm2 / 1.5 mm2 |
9 |
|
1 way switch |
3 |
1.0 mm2 / 1.5 mm2 |
(b).FAULTS THAT COULD CAUSE A SPLIT PHASE MOTOR TO HUM
- Open starting winding
- Grounded starting winding
- Burnt out starting winding
- Insufficient voltage
- Lack of grease/ceased/faulty bearing
- Mechanical overload/excess load
- Fault in transmission equipment
- Burnt switch contact
- Stuck centrifugal switch
- Misalignment or bent shaft
(c) HOW A SHADED POLE MOTOR RUNS
It runs from the unshaded to the shaded pole O R
When an a.c. is applied to the stator winding, a rotating magnetic field is generated.