Protective Devices

Question 1

Name as many protection devices as you can? (7 devices).

Answer 1

Earthing (not an actual protection device).
Fuses.
RCBO.
RCD.
MCB.
SPD.
AFDD.

Question 2

On a MCB what is the number in the enclosed box

Answer 2

This is the “Ka” number this is the breaking capacity of the device

Question 3

What will the Amps reach in a short circuit

Answer 3

The amps can reach hundreds or thousands in a short circuit

Question 4

How does an RCD work

Answer 4

Opening contacts when a fault is met causing the supply to be disconnected

Question 5

What does an RCD protect against

Answer 5

Earth faults

Question 6

What does an RCD protect

Answer 6

The person

Question 7

Does an RCD have overload protection

Answer 7

No only earth protection

Question 8

How many amps to kill a human?

Answer 8

Only 50mA

Question 9

What are some problems of RCD’s

Answer 9

Nuisance tripping
They are expensive
Cannot be used on fire protection circuits

TT systems don’t provide enough of a fault current to operate an RCD

Question 10

What are some advantages of an MCB

Answer 10

Tamper proof
Easy to reset
Operated differently depending on short circuit or overload fault

Question 11

What are some disadvantages of an MCB

Answer 11

Cost
Need to be tested regularly
Have moving parts
Temperature can affect operation

Question 12

What does RCBO stand for?

Answer 12

Residual Current operated circuit Breaker with integral Overcurrent protection.

Question 13

What does an RCBO protect against?

Answer 13

Overloads and short-circuits. An RCBO is basically a RCD and MCB in one.

Question 14

What does SPD stand for?

Answer 14

Surge Protective Device

Question 15

What do RCBO’s protect? (equipment or people)

Answer 15

RCBO’s are there to protect people however they will also protect equipment incase of over current.

Question 16

What do SPD’s protect? (Equipment of people)

Answer 16

SPD’s protect equipment.

Question 17

What does an SPD protect against?

Answer 17

SPD’s connect against power surges.

Question 18

What types of circuits are vulnerable to transient overvoltages (power surges)?

Answer 18

Safety circuits such as fire detection systems and emergency lighting circuits.

Question 19

Where is a type 1 SPD usually installed?

Answer 19

Installed at the origin. (Main distribution board)

Question 20

Where is a type 2 SPD usually installed?

Answer 20

Type 2 SPD’s are usually installed in sub distribution board.

Question 21

Where are combined type 1+2 SPD Installed ?

Answer 21

Combined type 1+2 SPD’s are usually installed in consumer units

Question 22

Where is a type 3 SPD usually installed?

Answer 22

Type 3 SPD’s are usually installed close to the protected load. These most only be installed as a supplement to a type 2 SPD.

Question 23

What does AFDD stand for?

Answer 23

Arc Fault Detection Device.

Question 24

What is an arc? And what causes them?

Answer 24

An arc is visible plasma discharges caused by current passing through a normally in conductive medium such as air.

Question 25

What temperatures do arcs reach?

Answer 25

Arcs can exceed 6000^oC.

Question 26

Where are AFDD mandatory?

Answer 26

1. Higher risk residential buildings (high rise buildings) 2. Houses in multiple occupation 3. Purpose-built student accommodation 4. Care homes

Question 27

What is a type “A” MCB used for?

Answer 27

Semi-conductor protection.

Question 28

What is a type “B” MCB used for?

Answer 28

Used in domestic installations.

Question 29

What is a type “C” MCB used for?

Answer 29

Used for fluorescent lights and commercial installations.

Question 30

What is a type “D” MCB used for?

Answer 30

High Inrush currents such as motors, welding equipment or X-ray’s

Question 31

What are the two ways protective devices operate?

Answer 31

Protective devices operate on Heat and Magnets.

Question 32

What is BS 3036?

Answer 32

Semi-enclosed (rewireable) fuse.

Question 33

What is the BS code for the semi-enclosed (rewireable) fuse?

Answer 33

BS 3036

Question 34

What are some advantages of the BS 3036 Semi-enclosed (rewireable) fuse?

Answer 34

1. Cheap 2. Apparent when blown

Question 35

What are some disadvantages of the BS 3036 Semi-enclosed (rewireable) fuse?

Answer 35

1. High fusing current (current needed to melt the wire in the fuse) 2. Low short circuit rating 3. Incorrect wire can be installed when replacing.

Question 36

What is BS88-2?

Answer 36

Cartridge type fuse HBC (high breaking capacity).

Question 37

What is the BS code for the cartridge fuse HBC (high breaking capacity).

Answer 37

BS88-2.

Question 38

How does the BS 3036 Semi-enclosed (rewireable) fuse work?

Answer 38

When there is a fault the wire heats up causing the wire to melt therefore the circuit to break.

Question 39

What is the breaking capacity of the cartridge fuse HBC (BS88-2)?

Answer 39

Up to 1250 amps = 80kA

Question 40

What are advantages of the the cartridge fuse HBC (BS88-2)?

Answer 40

1. Will not operate during short surges 2. Consistent in operation. 3. Accurate current rating. 4. Not liable to deterioration.

Question 41

What are disadvantages of the the cartridge fuse HBC (BS88-2)?

Answer 41

1. Expensive. 2. Can be replaced with a larger fuse rating.

Question 42

Where are the semi-enclosed (rewireable) BS 3036 fuses used?

Answer 42

Older installations

Question 43

What rating is the “White” BS 3036 Semi-enclosed (rewireable) fuse?

Answer 43

5 Amps.

Question 44

What rating is the “Blue” BS 3036 Semi-enclosed (rewireable) fuse?

Answer 44

15 Amps.

Question 45

What rating is the “Yellow” BS 3036 Semi-enclosed (rewireable) fuse?

Answer 45

20 Amps

Question 46

What rating is the “Red” BS 3036 Semi-enclosed (rewireable) fuse?

Answer 46

30 Amps

Question 47

What rating is the “Green” BS 3036 Semi-enclosed (rewireable) fuse?

Answer 47

45 Amps.

Question 48

Where are the cartridge fuse HBC (BS88-2) used?

Answer 48

In industrial applications.

Question 49

What is BS 1362?

Answer 49

Cartridge type fuse (1-45 Amps)

Question 50

What is BS 88-3

Answer 50

Cartridge fuse (above 45 Amps)

Question 51

What are the advantages of cartridge fuses BS 1362 and BS 88-3

Answer 51

1. Rating is written on the fuse body. 2. Does not deteriorate. 3. Circuit is isolated until replaced.

Question 52

What are the disadvantages of cartridge fuses BS 1362 and BS 88-3

Answer 52

1. Incorrect rating can be installed. 2. More expensive than rewireable. 3. Can be shorted out using metal. 4. Not apparent when blown.

Question 53

What is discrimination in an installation?

Answer 53

Ensuring that the protective device closest to the fault operates first. And keeping circuits separate.

Question 54

What size protective device would you use for a lighting circuit?

Answer 54

6A or 5A on the old reviewable fuses.