1. A roof mounted lamp as shown in Figure Q1 is used to provide the general lighting for a room. The illuminance measured directly below the lamp is 200 lux at point A. It is
assumed that the lights radiate uniformly in all downward directions from the lamps.

Figure Q1

(a) Determine the intensity of the lamp.

(b) Determine the illuminance at point B.

(c) If a new lamp of intensity 900 cd is mounted at the roof directly above point B, what will be the new illuminance at point B with both lamps turned on?

Name:______________________ Class:_______________ Electrical Installation (EEE4118)

Submission date: Assignment 2 Page 2 of 4

2. In Figure Q2, a single-phase, 220 V, 2.2 kW motor of power factor 0.84 and efficiency

0.79 is fed by a 6 mm2 2/C PVC/PVC copper cable. A 20 A BS88-2 HRC fuse is used

for protecting this circuit from short-circuit fault. Given that:

• the total cable length of the live and neutral conductor to form the circuit loop is 55 m;

• the resistance of the 6 mm2 cable during short circuit is 7 ? /km;

• the prospective short-circuit current at the 20 A BS88 HRC fuse is 6.5 kA.

Figure Q2

(a) Determine the minimum prospective short circuit current at the motor terminals.

(b)

If the starting current of the motor is 6 times full load current and lasts for 5

seconds, comment whether the 20 A BS88-2 HRC fuse is suitably selected or not,

with proper explanation. If not, determine the new minimum rating for the BS88-2

HRC fuse with proper explanation.

20 A BS88-2

HRC fuse

6 mm2 2/C PVC/PVC copper cable

Motor

Name:______________________ Class:_______________ Electrical Installation (EEE4118)

Submission date: Assignment 2 Page 3 of 4

Name:______________________ Class:_______________ Electrical Installation (EEE4118)

Submission date: Assignment 2 Page 4 of 4

3. In Figure Q3, a 220 V a.c. equipment, which is located in an equipotential zone, is

protected by a 32 A BS88-2 HRC fuse and fed by a 6 mm2 1/C PVC insulated copper

cable. A separate 4 mm2 1/C PVC copper cable is used as the circuit protective

conductor (CPC) for the installation. Given that:

• the cable length measured from the MCB board to the equipment is 45 m

• the impedance of 6 mm2 copper cable (each conductor) is 3.65 m?/m

• the impedance of 4 mm2 copper cable (each CPC conductor) is 5.5 m?/m

• the earth fault loop impedance external to the installation (ZE) is 0.4 ?

• k factor of the CPC is 115

Determine:

(a) the prospective earth fault current of the installation,

(b) whether the disconnected time of the fuse due to the earth fault can fulfill the

requirement of the CoP for the Electricity (Wiring) Regulations, and

220V