Protection

Question 1

define fusing/tripping current

Answer 1

The minimum current at which a fuse element will begin to rupture or breaker trip.

Question 2

define rupturing capacity (rated breaking capacity)

Answer 2

The maximum fault current that a protective device can
safely stop flowing.

Question 3

When does close excess current protection become course excess current protection?

Answer 3

Close is within 4 hours at 1.5 times load current. Course is not.

Question 4

Rewireable fuse breaking capacity

Answer 4

Usually limited to 1,000A

Question 5

HRC fuse breaking capacity

Answer 5

Up to 80,000A

Question 6

MCB breaking capacity

Answer 6

Up to 9,000A

Question 7

What is an SRCD

Answer 7

RCCB socket outlet unit

Question 8

What is an RCBO?

Answer 8

RCD’s that have integral circuit-breakers built into them, providing both personal protection and protection against
overcurrent.

Question 9

What is an PRCD?

Answer 9

portable RCD

Question 10

RCD operation current/time normally vs in schools

Answer 10

For personal protection, the RCD has a maximum rated residual operating current of 30mA and it operates within a maximum time of 300ms (0.3s)

electro-medical locations must have maximum rated residual operating current of 10mA and disconnect the supply within 40mS (0.04s)

Question 11

What is an RCCB

Answer 11

Residual current circuit breakers do not have circuit overload protection and are available in a range of types

Question 12

What is the fusing factor equation?

Answer 12

Fusing Factor =
min fusing current/fuse current rating