Domestic Circuits…
There are two types of circuits used within all electrical installations including domestic and they are…
Radial Circuits
These are individual circuits which start at the consumer unit, fed via their own protective device and loop in and out as a chain until they reach their end point. The most common examples of radial circuits are lighting, showers and cookers.
Ring Circuits
Used in the UK to supply socket circuits, the ring circuit starts at the consumer unit fed via its own protective device and loops in and out of each socket outlet before returning to the to the consumer unit and connecting to the same protective device etc that it started out from.
Supplying Circuits
Due to multiple regulations within the current 18th Edition of BS7671 as well as overload protection all circuits within a domestic installation also need to be provided with 30mA RCD fault protection.
This can be done using one of two available methods…
1: Using a ‘split load’ consumer unit in which an individual circuit is provided with overload protection by connecting it to its own circuit breaker and then multiple circuits are protected collectively using a 30mA residual current circuit breaker ‘RCCB’ to provide fault protection. Or…
2: Protecting each circuit individually with one single device called a residual current circuit breaker with overload protection ‘RCBO’ that provides both overload and fault protection by combining the function of a circuit breaker and a 30mA RCD in one device.
Due to the cost of individual RCBOs the most common method used is the split load board, but care should be taken to minimise any disruption that may be caused if an RCCB trips which will disconnect the supply to multiple circuits around the home and not just the circuit with the fault.
Circuit wiring…
Lighting circuits.
As mentioned, lighting circuits are connected as radial circuits and the most common one used for domestic lighting is often called the ‘loop in’ method. This circuit is wired using 1.0mm or 1.5 mm Twin and Earth which starts at the consumer unit protected by a 6A type B circuit breaker and 30mA RCCB or a combined 6A/30mA RCBO device.
After leaving the consumer unit the Twin and Earth cable carrying the Line, Neutral and CPC ‘loops in’ and out of the ceiling rose in each room until it reaches the last light/room where it stops. The line connects to the central ‘loop’ connection which has three terminals and the neutral goes in the other three terminal connection along with the Neutral of the lamp holder. All of the CPCs connect to the large earth terminal.
Switching is done by taking a Twin and Earth down to the light switch from the ceiling rose where the brown conductor connects into the central loop connection taking a line 230V feed down to the switch where it connects to the common terminal on the light switch. The blue conductor goes into the L1 connection on the light switch and returns back to the ceiling rose where it connects to the two terminal connections along with the brown line conductor of the lamp holder. This type of light switch with just two connections is called a one-way switch.
This blue conductor coming up from the light switch to the ceiling rose is not a neutral conductor but is in fact a line conductor that carries 230V back up to the light when the switch is closed making the light come on and is known as a switched line/live and as such it needs to be identified as a line conductor with brown sleeving or tape at both the ceiling rose and the light switch.
The CPC usually connects to the backbox and needs to be connected to any metal switch plates.
Switching more than one light on at a time can be achieved by connecting any additional ceiling rose/s into the neutral and switched line connections of both the main and any additional ceiling rose using a Twin and Earth cable. Care should be taken as the main ceiling rose can become quite crowded.
Two-Way Switching…
When a single light needs to be switched on or off from two positions which is usually the case on stairs or landings a two-way lighting switch arrangement can be used. The most common and easiest way of doing this is to link both of the light switches together using a 3-core and CPC PVC cable and have a Twin and Earth cable connecting one of the switches to the ceiling rose of the light to be switched.
The switches used in this instance are two-way switches and have three connections which are called common, L1 and L2. The Twin and Earth cable connects at the ceiling rose the same way as previously with the brown in the central ‘loop’ connection and the blue in the two terminal connection along with the brown line conductor of the lamp holder. Don’t forget the brown sleeving on this blue conductor as before.
At the first switch we have the brown, blue and CPC of the Twin and Earth and along with the brown, black, grey and CPC of the 3-core cable. The brown of the 3-core connects to the common on the light switch and the black of the 3-core along with the brown of the Twin and Earth go together into terminal L1 of the switch. This leaves the grey of the 3-core and blue of the Twin and Earth and these go together into the L2 connection of the switch.
On the second switch the 3-core connects to the same terminals as the first switch. Brown, common. Black, L1 and grey, L2. All CPCs should be connected to terminals on the backboxes and switch plates as necessary.
If needed additional switching positions can be added through the use of intermediate lighting switches which are placed between the two-way switches.