Circuits and heating methods

Question 1

What are all lighting points unless specific light sources with known power ratings assumed power ratings?

Answer 1

100Watts

Question 2

To prevent against a complete blackout in the event of a fault how many lighting circuits should be installed i a premises?

Answer 2

a minimum of two lighting circuits should be installed in a premises

Question 3

Should earthing and CPC be provided to all lighting points including switches?

Answer 3

Yes all lighting points and switches should have an earthing terminal and CPC

Question 4

What size of protective device are normally used in domestic lighting circuits?

Answer 4

5 and 6 amp devices are normally used

Question 5

What size of protective device should there be in a lighting circuit protected by a semi-enclosed fuse?

Answer 5

5 Amp

Question 6

What size of protective device should there be in a lighting circuit protected by a circuit breaker?

Answer 6

6 Amp

Question 7

What is a two plate wiring system?

Answer 7

In two plate wiring the live conductor feeds the switch before the ceiling rose/junction box.
Typically wired in ‘conduit method’ in single core cable.
Used in commercial and industrial settings

Question 8

What is a 3 plate wiring system?

Answer 8

Is for circuits wired in composite cables
The ceiling rose contains a third terminal ‘Three plate’
The connection point is referred to as the ‘loop in’

Question 9

Which conductor must single pole switches and protective devices be installed on?

Answer 9

The live conductor only must have single pole switches and protective devices installed

Question 10

In an Edison screw lamp holder what contact is used for the earthing terminal?

Answer 10

The middle contact is used for the earthing terminal

Question 11

What are the two types of power circuits

Answer 11

Ring-main / Ring final

Radial

Question 12

What is the maximum floor area a ring final circuit can cover?

Answer 12

A ring final circuit can supply an unlimited number of sockets outlets in a 100 m2 floor area.

Question 13

What is a benefit of a ring final circuit?

Answer 13

They assist in improving voltage drop as the circuit load is shared by two conductors in parallel.

Question 14

What is a disadvantage of a ring final circuit?

Answer 14

If the circuit becomes an open circuit, circuit conductors may become overloaded leading to the possibility of a fire.

Question 15

How do you calculate diversity in a cooker?

Answer 15

The first 10A are 100% and the remaining assumed current is 30% plus 5 Amps if there is a socket outlet

Question 16

What is the maximum floor area of an A2 radial circuit?

Answer 16

75 m2

Question 17

What is the maximum floor area of an A3 radial circuit?

Answer 17

50 m2

Question 18

What size of cable and protective device is used for an A2 radial circuit?

Answer 18

4mm2 cable and 30-32A Breaker

Question 19

What size of cable and protective device is used for an A3 Radial circuit

Answer 19

2.5mm2 and 20 Amp breaker

Question 20

What is the definition of a spur?

Answer 20

A spur is defined as a branch from a ring or a radial final circuit

Question 21

Name two ways of connecting a spur into a ring final or radial final circuit?

Answer 21

A spur can be connected using a joint box of an appropriate rating or be connected directly to an outlet on the circuit. (The box must be accessible for inspection and testing)

Question 22

How many spurs are aloud in a ring final circuit?

Answer 22

The number of spurs must not exceed the number of outlets in the final circuit

Question 23

How many outlets are aloud per unfused spur?

Answer 23

Only one outlet is aloud per unused spur this can be a single or twin socket.

Question 24

How many outlets are aloud when connecting a fused spur?

Answer 24

There are no number of maximum outlets aloud per unfused spur

Question 25

How many socket circuits should be installed as a minimum on a premises?

Answer 25

There should be at least two socket circuits installed as a minimum in the event of a failure you will continue to have electricity

Question 26

Why should the number of circuits installed have an equal number of outlets connected?

Answer 26

This is to ensure there is balanced loading

Question 27

Why should a kitchen have a separate socket circuit?

Answer 27

Due to the large number of appliances

Question 28

Describe how a Convection heater works

Answer 28

They either warm air directly or heat oil which in turn transfers heat to the air. this then warms people and objects in the room.

Question 29

Where is a convection heater best suited?

Answer 29

Well insulated rooms

Question 30

How does a radiant heater work?

Answer 30

Usually comprised of tungsten filaments in heat-resistant quartz envelopes mounted in front of a metal reflector in a plastic or metal case. They operate like a light bulb but radiate the energy in the infrared spectrum. Convert upto 88% of input power to radiant energy, loosing remainder to convection and conductive heat.

Question 31

What is an advantage of a radiant heater and where is it more suitably used?

Answer 31

The advantage of a radiant heater is that the heat produced is absorbed directly into the skin without heating surroundings first. This makes them more suited for poorly insulated rooms

Question 32

Describe underfloor heating

Answer 32

Underfloor heating is a series of wires usually on top of a layer of screed. Can be used on multiple different surfaces. This then heats up the surface of the floor

Question 33

What are the three main types of underfloor heating?

Answer 33

Loose fit wiring - Flexible enough to fit in small awkward spaces
Electric cable systems
Heating mats you roll out to cover larger areas

Question 34

Describe how a storage heater works?

Answer 34

Heat retaining clay bricks are charged over night to release heat through out the day. They use convection and radiant heat. They benefit consumers with economy 7 electricity supply as it is designed to save money