Protective Devices Flashcards
Name as many protection devices as you can? (7 devices).
Earthing (not an actual protection device).
Fuses.
RCBO.
RCD.
MCB.
SPD.
AFDD.
On a MCB what is the number in the enclosed box
This is the “Ka” number this is the breaking capacity of the device
What will the Amps reach in a short circuit
The amps can reach hundreds or thousands in a short circuit
How does an RCD work
Opening contacts when a fault is met causing the supply to be disconnected
What does an RCD protect against
Earth faults
What does an RCD protect
The person
Does an RCD have overload protection
No only earth protection
How many amps to kill a human?
Only 50mA
What are some problems of RCD’s
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
What are some advantages of an MCB
Tamper proof
Easy to reset
Operated differently depending on short circuit or overload fault
What are some disadvantages of an MCB
Cost
Need to be tested regularly
Have moving parts
Temperature can affect operation
What does RCBO stand for?
Residual Current operated circuit Breaker with integral Overcurrent protection.
What does an RCBO protect against?
Overloads and short-circuits. An RCBO is basically a RCD and MCB in one.
What does SPD stand for?
Surge Protective Device
What do RCBO’s protect? (equipment or people)
RCBO’s are there to protect people however they will also protect equipment incase of over current.
What do SPD’s protect? (Equipment of people)
SPD’s protect equipment.
What does an SPD protect against?
SPD’s connect against power surges.
What types of circuits are vulnerable to transient overvoltages (power surges)?
Safety circuits such as fire detection systems and emergency lighting circuits.
Where is a type 1 SPD usually installed?
Installed at the origin. (Main distribution board)
Where is a type 2 SPD usually installed?
Type 2 SPD’s are usually installed in sub distribution board.
Where are combined type 1+2 SPD Installed ?
Combined type 1+2 SPD’s are usually installed in consumer units
Where is a type 3 SPD usually installed?
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.
What does AFDD stand for?
Arc Fault Detection Device.
What is an arc? And what causes them?
An arc is visible plasma discharges caused by current passing through a normally in conductive medium such as air.
What temperatures do arcs reach?
Arcs can exceed 6000oC.
Where are AFDD mandatory?
- Higher risk residential buildings (high rise buildings)
- Houses in multiple occupation
- Purpose-built student accommodation
- Care homes
What is a type “A” MCB used for?
Semi-conductor protection.
What is a type “B” MCB used for?
Used in domestic installations.
What is a type “C” MCB used for?
Used for fluorescent lights and commercial installations.
What is a type “D” MCB used for?
High Inrush currents such as motors, welding equipment or X-ray’s
What are the two ways protective devices operate?
Protective devices operate on Heat and Magnets.
What is BS 3036?
Semi-enclosed (rewireable) fuse.
What is the BS code for the semi-enclosed (rewireable) fuse?
BS 3036
What are some advantages of the BS 3036 Semi-enclosed (rewireable) fuse?
- Cheap
- Apparent when blown
What are some disadvantages of the BS 3036 Semi-enclosed (rewireable) fuse?
- High fusing current (current needed to melt the wire in the fuse)
- Low short circuit rating
- Incorrect wire can be installed when replacing.
What is BS88-2?
Cartridge type fuse HBC (high breaking capacity).
What is the BS code for the cartridge fuse HBC (high breaking capacity).
BS88-2.
How does the BS 3036 Semi-enclosed (rewireable) fuse work?
When there is a fault the wire heats up causing the wire to melt therefore the circuit to break.
What is the breaking capacity of the cartridge fuse HBC (BS88-2)?
Up to 1250 amps = 80kA
What are advantages of the the cartridge fuse HBC (BS88-2)?
- Will not operate during short surges
- Consistent in operation.
- Accurate current rating.
- Not liable to deterioration.
What are disadvantages of the the cartridge fuse HBC (BS88-2)?
- Expensive.
- Can be replaced with a larger fuse rating.
Where are the semi-enclosed (rewireable) BS 3036 fuses used?
Older installations
What rating is the “White” BS 3036 Semi-enclosed (rewireable) fuse?
5 Amps.
What rating is the “Blue” BS 3036 Semi-enclosed (rewireable) fuse?
15 Amps.
What rating is the “Yellow” BS 3036 Semi-enclosed (rewireable) fuse?
20 Amps
What rating is the “Red” BS 3036 Semi-enclosed (rewireable) fuse?
30 Amps
What rating is the “Green” BS 3036 Semi-enclosed (rewireable) fuse?
45 Amps.
Where are the cartridge fuse HBC (BS88-2) used?
In industrial applications.
What is BS 1362?
Cartridge type fuse (1-45 Amps)
What is BS 88-3
Cartridge fuse (above 45 Amps)
What are the advantages of cartridge fuses BS 1362 and BS 88-3
- Rating is written on the fuse body.
- Does not deteriorate.
- Circuit is isolated until replaced.
What are the disadvantages of cartridge fuses BS 1362 and BS 88-3
- Incorrect rating can be installed.
- More expensive than rewireable.
- Can be shorted out using metal.
- Not apparent when blown.
What is discrimination in an installation?
Ensuring that the protective device closest to the fault operates first. And keeping circuits separate.
What size protective device would you use for a lighting circuit?
6A or 5A on the old reviewable fuses.