Circuits and heating methods Flashcards
What are all lighting points unless specific light sources with known power ratings assumed power ratings?
100Watts
To prevent against a complete blackout in the event of a fault how many lighting circuits should be installed i a premises?
a minimum of two lighting circuits should be installed in a premises
Should earthing and CPC be provided to all lighting points including switches?
Yes all lighting points and switches should have an earthing terminal and CPC
What size of protective device are normally used in domestic lighting circuits?
5 and 6 amp devices are normally used
What size of protective device should there be in a lighting circuit protected by a semi-enclosed fuse?
5 Amp
What size of protective device should there be in a lighting circuit protected by a circuit breaker?
6 Amp
What is a two plate wiring system?
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
What is a 3 plate wiring system?
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’
Which conductor must single pole switches and protective devices be installed on?
The live conductor only must have single pole switches and protective devices installed
In an Edison screw lamp holder what contact is used for the earthing terminal?
The middle contact is used for the earthing terminal
What are the two types of power circuits
Ring-main / Ring final
Radial
What is the maximum floor area a ring final circuit can cover?
A ring final circuit can supply an unlimited number of sockets outlets in a 100 m2 floor area.
What is a benefit of a ring final circuit?
They assist in improving voltage drop as the circuit load is shared by two conductors in parallel.
What is a disadvantage of a ring final circuit?
If the circuit becomes an open circuit, circuit conductors may become overloaded leading to the possibility of a fire.
How do you calculate diversity in a cooker?
The first 10A are 100% and the remaining assumed current is 30% plus 5 Amps if there is a socket outlet
What is the maximum floor area of an A2 radial circuit?
75 m2
What is the maximum floor area of an A3 radial circuit?
50 m2
What size of cable and protective device is used for an A2 radial circuit?
4mm2 cable and 30-32A Breaker
What size of cable and protective device is used for an A3 Radial circuit
2.5mm2 and 20 Amp breaker
What is the definition of a spur?
A spur is defined as a branch from a ring or a radial final circuit
Name two ways of connecting a spur into a ring final or radial final circuit?
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)
How many spurs are aloud in a ring final circuit?
The number of spurs must not exceed the number of outlets in the final circuit
How many outlets are aloud per unfused spur?
Only one outlet is aloud per unused spur this can be a single or twin socket.
How many outlets are aloud when connecting a fused spur?
There are no number of maximum outlets aloud per unfused spur
How many socket circuits should be installed as a minimum on a premises?
There should be at least two socket circuits installed as a minimum in the event of a failure you will continue to have electricity
Why should the number of circuits installed have an equal number of outlets connected?
This is to ensure there is balanced loading
Why should a kitchen have a separate socket circuit?
Due to the large number of appliances
Describe how a Convection heater works
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.
Where is a convection heater best suited?
Well insulated rooms
How does a radiant heater work?
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.
What is an advantage of a radiant heater and where is it more suitably used?
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
Describe underfloor heating
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
What are the three main types of underfloor heating?
Loose fit wiring - Flexible enough to fit in small awkward spaces
Electric cable systems
Heating mats you roll out to cover larger areas
Describe how a storage heater works?
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
