Sim's Electrical Companion
Quick links - Drawings & Symbols
Plan drawings are commonly used to indicate where electrical services are going to be installed. To make this universally understood there are standard symbols to indicate what each of the components are.
You can make up your own symbols where necessary if you include a key so anyone else that needs to use the plan can decipher your intention.
Circuit Diagrams
Layout & Exploded Diagrams
A layout diagram will show where components are desired to be located. The diagram is a visual representation of what the installation should look like.
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Though rarely used for electrical installations there are some occasions where they may be of use. The example illustration shows the desired layout of a photo voltaic (PV) secondary source of supply.
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This shows clearly where the elements are to be installed and how. Layouts can either be to scale or just give a visual representation of the desired layout.
Exploded View of a Car Starter Motor
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An exploded view of an object can visually represent the order parts go together and where they connect to this can be of great help in understanding how a device works and what may be wrong when they do not.
Wiring Diagrams
Unlike circuit diagrams which show the electrical path in a simple form wiring diagrams give much greater detail on all of the circuit connections. Colour coding is used for the circuit live and protective conductors. Wiring diagrams do not give details on cable runs like distance and positioning. Their main purpose is to show how the system is connected and what accessories are connected.
The symbols I use are all shown below with an explanation where necessary. Some diagrams from other sources may vary and you may develop your own method. Clarity is the key to an effective wiring diagram.
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Accessory Symbols - Single Phase consumer unit / distribution board
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Circuit numbers are counted by module from the main switch right to left in this example. This is also the case for neutral and circuit protective conductors.
The main earth and bonding connection are on the left hand side of the earth bar Labelled E & B.
This example shows three installed circuit breakers. The main incommer and main earth are omitted in most of my diagrams in order to make them easier to read. I do, however, include them on distribution diagrams.
Three Phase Consumer Unit / Distribution Board
Circuit numbers are counted by module from the top of the left hand side down towards the main switch and then from the top of the right hand side down to the main switch.
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I have arranged this board in a similar fashion to how they are manufactured. Once again other methods can be used as long as the connections are clearly understood.
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I have Included two linked neutral bars & two linked earthing bars to make wiring diagrams easier to arrange.
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The main incomer is a linked 3 pole isolator which would isolate L1, L2 & L3 at the same time. Some arrangements have a four pole isolator that additionally isolates the Neutral. These are referred to as TP-N (Three Phase & Neutral).
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When arranging a board like this it is worth applying some thought to load balancing the phases. When added together L1, L2 & L3 in an ideal scenario would be carrying essentially the same amount of current.
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The example shows well balanced phase loads:
L1: 20A + 32A + 6A + 20A = 78A
L2: 20A + 20A + 20A + 20A = 80A
L3: 20A + 6A + 32A + 20A = 78A
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A different arrangement may be very poorly balanced:
L1: 20A + 32A + 32A + 20A = 104A
L2: 20A + 20A + 20A + 20A = 80A
L3: 20A + 20A + 6A + 6A = 52A
Common accessories wiring diagram symbols disclaimer - The symbols presented here are based on ones I have seen and some are of my own design, other versions do exist. Clarity is of the utmost importance for a wiring diagram but alternatives to these symbols presented may be used.
1 Way Lighting
Lighting systems can be a bit of a head scratcher as there are many ways of achieving the same desired effect. It is quite common for them to be added to and not identified correctly so great care should be taken when working on an existing system. Some conventions prevail and in this section I will show a few methods of installing domestic / light commercial lighting using the conduit method with PVC single cables and the PVC/PVC method using multicore cables.
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Each system may be fed by the switch, Loop or junction box. For all the methods shown here extra lights may be installed to be controlled at the same time by extending from the switched line and neutral of the first light that is being controlled. . When choosing which method to adopt it is usually dictated by the building layout and its method of construction. Most houses with a loft space or offices with a suspended ceiling will adopt the loop in or junction method to feed the lighting to the floor below as it is the simplest method.
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One convention that is worth a mention is in the case of one way lighting it is normal to have the light switch at the entrance of the room with the on position as shown below.
Extra Lamps from One Form of Control
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More than one light may be controlled from the switching arrangement. The amount of extra lights that can be fed from a single method of control is limited by the current that the switch can safely disconnect on load. Commonly domestic lighting is fed by a 5A fuse or a more modern 6A circuit breaker. Allow 100W per lamp or less if the fitting cannot be fitted with a 100W lamp for example GU10 ≤ 50W. To control more than one light the diagram below shows one method. Junction boxes may be used where more connections are required.
Applying power law gives us the option of installing:
6A x 230V = 1380W
ES or BC lamps:
1380W / 100 = 13.8 so 13 lamps
GU10 50W
1380W / 50 = 27.6 or 27 lamps
2 Way Lighting
Two way lighting is most commonly found in rooms with two entrances, hotel bedside control, corridors and at staircases. This allows control from two points and has several more methods of installation. The cables running between the switches are called strappers and must be arranged correctly to have the lights function as intended in all the switch position combinations. If the Junction box (JB) method of supplying the lights is used the JB must be accessible for testing, inspection or future modifications. The JB may be concealed if it is certified Maintenance Free by the manufacturer and stamped with the symbol MF with a circle around it:
Two Way Junction Method
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The diagram is to demonstrate that circuits or individual rooms can be served by a junction box. This allows multiple lighting circuits to be added. I have just added two so the diagram is not over complicated. Note where conductors cross over each other it is not a connection unless there is a circle showing that it is a termination.
Intermediate Lighting
When more than two points of lighting control are needed intermediate switches are employed. They have the effect of reversing whatever state the control system is in. If it is off they turn it on or vice versa. Areas where you may need more than two points of control include large halls, hotel bedside control & long corridors etc.
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Intermediate switching is often incorrectly named three way switching however the amount of intermediate switches is essentially unlimited within reason. They do require a two way control at each end of the control circuit. An Intermediate switch can be used as a two way switch but a two way switch cannot perform the same task as an intermediate switch.
Example uses of intermediate switching:
Corridors, hotel bedrooms, Large halls and rooms with multiple entrances.
S Plan Heating Control
S Plan Heating employs two separate two port valves. They are for independent control of heating and hot water. When hot water is being called for the programmer will engage the boiler, pump and open the two port valve. When the water is up to temperature the cylinder stat will disengage the heat.
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Heating is controlled by the programmer and is engaged up to the required temperature detected by the room stat' (thermostat). When heating is being called for the boiler and pump are engaged. The heating two port valve is opened.
Y Plan Heating Control
Y Plan Heating employs a single three port valve. The valve can provide independent control of heating and hot water in a single unit. When hot water is being called for the programmer will engage the boiler, pump and open the three port valve. When the water is up to temperature the cylinder stat will disengage the heat.
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Heating is controlled by the programmer and is engaged up to the required temperature detected by the room stat' (thermostat). When heating is being called for the boiler and pump are engaged. The heating three port valve is opened.
