Basic electrical circuitry & applications Aims: To explore different wiring methods for lighting and power circuits. Outcomes: State the different parts of an electrical circuit Draw different lighting circuits Draw a ring final socket circuit

Component parts of an electrical circuit. The BS7671 defines a circuit as ‘an assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective devices’. Here is a list of components that make up an electrical circuit: Source of supply Circuit conductors (cable) Circuit protection Circuit control Load

Source of supply: For current to flow two conditions have to be met. There has to be a potential difference applied across the circuit. (voltage) There has to be a complete circuit (circle) for current to flow around. There are two types of supply. What are they?

A.C voltage and D.C voltage. For an a.c. supply, either an a.c. generator or d.c. generator with components to rectify the supply, can be used. If a d.c. supply is required, then this is derived from a battery. The size and type of voltage required for the supply is determined by the load equipment being used. A plate will usually be attached to the equipment indicating its safe working voltage and other requirements.

Circuit conductors: The circuit conductors are those parts of the circuit that the current passes through. These are the cables. There are two parts to a cable. One is the conductor itself. This is usually made from copper. The other is the insulation, usually made from PVC, which forms a sheath around the conductor. The insulation is required to: Prevent the conductors touching together; this could short the circuit and stop it from working. Prevent users of the circuit from coming into contact with the conductors and receiving an electric shock. The type of insulation required is determined by the voltage which is to be applied to the cable.

Circuit protection: Every circuit requires protection if, in the event of a fault, damage is to be avoided. This is usually by the way of a suitably rated fuse or protective device. Such a device is called a miniature circuit breaker (MCB). This will protect both the load and the cables supplying the load, from the heat damage associated with large fault current. There are various sizes and types of fuses, which include: BS 3036 rewirable fuses BS 1361 cartridge fuses BS EN 60898 MCB’s BS EN 61009 RCBO’s

Circuit control: It is important that a circuit, no matter its level of complexity, can be controlled. This could be either: A simple switch, allowing you to turn the circuit on or off A time switch, which activates the circuit at certain times Can you think of any thing you may use in everyday life that can be thought of as a switch?

Load: The load refers to the item that requires the supply in order to function. This could be the lights in a circuit, a heater, a motor to drive a pump or any item of equipment (or combinations) that require an electrical supply in order for them to work. Electrical loads are rated in watts or kilowatts (W and kW). The size of the load is generally stamped on the equipment or marked on a name plate. On the plate it should state: Rating in watts Frequency of the supply Supply voltage Full load current If this information is not available on the plate, then will need to contact the manufacturer.

Basic lighting circuit diagram

One way lighting circuit Below is a diagram of a one way lighting circuit using the “loop in” method. This is sometimes called the “3 plate” method. The “loop in” method is done by taking the supply cable to the lighting point (ceiling rose). From here a switch cable is taken to the switch plate. Then the supply cable continues from the lighting point to the next lighting point and so on till it finishes at the last light on the circuit. This method can also be done using a junction box.

Two way lighting circuit Here is a lighting circuit that is controlled by two switch’s. Again this is the “loop in” or “3 plate” method of wiring. You would normally use two way lighting circuits on hall ways and landings.

Two way & intermediate lighting circuit Two way & intermediate lighting circuits would be used where there is more than two floors i.e. a three storey house.

Sockets circuits There a two types of sockets circuits. Ring final circuits Radial circuit Basically the ring final circuit (RFC) starts at the consumer unit, goes to each socket, than back to the consumer unit (like a ring). A radial circuit, starts at the consumer unit, goes to each socket and finishes at the last socket on the circuit. It can also branch off from each socket to numerous sockets (like a tree branch).

Ring final circuit (RFC) Below is a diagram of a ring final socket circuit. You can add a spur from each socket or junction box but only once.

Radial circuit Here we have a diagram of radial socket circuit. Radial circuits are also used for a number of different applications. Can you think of any you may have seen or even use in everyday life?