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College > Protective Devices > Flashcards

Protective Devices Flashcards

1
Q

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

A

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

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2
Q

On a MCB what is the number in the enclosed box

A

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

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3
Q

What will the Amps reach in a short circuit

A

The amps can reach hundreds or thousands in a short circuit

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4
Q

How does an RCD work

A

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

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5
Q

What does an RCD protect against

A

Earth faults

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6
Q

What does an RCD protect

A

The person

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7
Q

Does an RCD have overload protection

A

No only earth protection

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8
Q

How many amps to kill a human?

A

Only 50mA

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9
Q

What are some problems of RCD’s

A

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

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10
Q

What are some advantages of an MCB

A

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

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11
Q

What are some disadvantages of an MCB

A

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

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12
Q

What does RCBO stand for?

A

Residual Current operated circuit Breaker with integral Overcurrent protection.

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13
Q

What does an RCBO protect against?

A

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

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14
Q

What does SPD stand for?

A

Surge Protective Device

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15
Q

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

A

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

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16
Q

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

A

SPD’s protect equipment.

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17
Q

What does an SPD protect against?

A

SPD’s connect against power surges.

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18
Q

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

A

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

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19
Q

Where is a type 1 SPD usually installed?

A

Installed at the origin. (Main distribution board)

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20
Q

Where is a type 2 SPD usually installed?

A

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

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21
Q

Where are combined type 1+2 SPD Installed ?

A

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

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22
Q

Where is a type 3 SPD usually installed?

A

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.

23
Q

What does AFDD stand for?

A

Arc Fault Detection Device.

24
Q

What is an arc? And what causes them?

A

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

25
Q

What temperatures do arcs reach?

A

Arcs can exceed 6000oC.

26
Q

Where are AFDD mandatory?

A
  1. Higher risk residential buildings (high rise buildings)
  2. Houses in multiple occupation
  3. Purpose-built student accommodation
  4. Care homes
27
Q

What is a type “A” MCB used for?

A

Semi-conductor protection.

28
Q

What is a type “B” MCB used for?

A

Used in domestic installations.

29
Q

What is a type “C” MCB used for?

A

Used for fluorescent lights and commercial installations.

30
Q

What is a type “D” MCB used for?

A

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

31
Q

What are the two ways protective devices operate?

A

Protective devices operate on Heat and Magnets.

32
Q

What is BS 3036?

A

Semi-enclosed (rewireable) fuse.

33
Q

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

A

BS 3036

34
Q

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

A
  1. Cheap
  2. Apparent when blown
35
Q

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

A
  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.
36
Q

What is BS88-2?

A

Cartridge type fuse HBC (high breaking capacity).

37
Q

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

A

BS88-2.

38
Q

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

A

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

39
Q

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

A

Up to 1250 amps = 80kA

40
Q

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

A
  1. Will not operate during short surges
  2. Consistent in operation.
  3. Accurate current rating.
  4. Not liable to deterioration.
41
Q

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

A
  1. Expensive.
  2. Can be replaced with a larger fuse rating.
42
Q

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

A

Older installations

43
Q

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

A

5 Amps.

44
Q

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

A

15 Amps.

45
Q

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

A

20 Amps

46
Q

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

A

30 Amps

47
Q

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

A

45 Amps.

48
Q

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

A

In industrial applications.

49
Q

What is BS 1362?

A

Cartridge type fuse (1-45 Amps)

50
Q

What is BS 88-3

A

Cartridge fuse (above 45 Amps)

51
Q

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

A
  1. Rating is written on the fuse body.
  2. Does not deteriorate.
  3. Circuit is isolated until replaced.
52
Q

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

A
  1. Incorrect rating can be installed.
  2. More expensive than rewireable.
  3. Can be shorted out using metal.
  4. Not apparent when blown.
53
Q

What is discrimination in an installation?

A

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

54
Q

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

A

6A or 5A on the old reviewable fuses.

College (21 decks)

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