ICIT Revision D

Which one of the following provisions is to enable proper functioning and control of current-using equipment for installation user?

• Isolation

• Functional switching.

• Emergency switching.

• Switching off for mechanical maintenance.

   

The transformer used for distribution is 3-phase 4-wire system with star point connected to earth is

• Delta-Delta Step-Down Transformer

• Delta-Star Step-Down Transformer

• Star-Star Step-Down Transformer

• Star-Delta Step-Down Transformer

Answer explanation

the transformer used to step-down from 22kV to 400V, 50 Hz supply is Delta- Star connected transformer, the star point at secondary side (400V) is connected to earth.

In Singapore, the voltage between any two phases is 400V, 50 Hz and between any phase and the neutral is

• 230V, 50 Hz.

• 240V, 50 Hz.

• 230V, 60 Hz.

• 240V, 60 Hz.

Answer explanation

Our single-phase voltage is 230 V, 50 Hz.

Small non-domestic consumers, like flatted factories having industrial

loads are supplied with a 3-phase, 4-wire service cable to provide 230 V,

50 Hz single-phase and

• 400 V, 50 Hz three-phase.

• 415 V, 50 Hz three-phase.

• 400 V, 60 Hz three-phase.

• 415 V, 60 Hz three-phase.

In order to balance the three phases system, consecutive services are connected to different phases and neutral in turn to

• reducing the current in the neutral

• so keeping the running costs up

• increasing the current in the phase

• increasing the current in the neutral

The maximum electricity supply capacity for single-phase 230 V, 50 Hz provided by SP Services Ltd (SPSL) is

• 15 kVA

• 23 kVA

• 45 kVA

• 75 kVA

Answer explanation

Supply capacity at 230V, 50 Hz provided by SPSL is maximum 23 kVA or 100 A.

more than this will need 3-phase 400 V, 50Hz supply.

As in distribution system, it is important that the load currents are equally divided over the three phases to

• improve the power factor

• reduced the voltage drop on conductor.

• .reduced the total power consumption.

• balanced the current demand of the incoming supply.

In a 3-phase 4 wires distribution system, the neutral conductor only carries the

• high power factor current

• low power factor current.

• out-of-frequency current.

• out-of-balance current.

The supply to each floor is connected to the rising main by means of

• tap-off units

• switch-off units

• distribution units.

• transmission units.

All distribution boards shall be provided with a legible diagram indicated the method used for protection against

• fire.

• direct contact.

• indirect contact.

• lightning surge.