CONTENT
A. Who this blog is for.
B. Why I choose house electrical symbols.
C. Background of the example electrical drawings.
D. What is on the drawings.
E. Note of caution: ELECTRICITY IS DANGEROUS. IT KILLS.
A. Who this blog is for?
I started this blog because I have tons of materials on this subject. I already have a number of other blogs on electrical installations and other similar electrical topics. When I when check my blog statistics, I always see some considerable traffic from google and yahoo search engines coming to my site looking for materials on electrical symbols.
So I thought to myself… Why not? Lots of people are looking for this information, so why don’t I just give it to them? I may even get a few extra dollars from advertising for the effort.
However, people looking for guides on electrical symbols are beginners. I know there are many AutoCAD (and other types of CAD programs) technicians and operators online but these people are in the expert category and they no longer need guides on electrical symbols or drawing symbols. At most, they would be surfing around looking for some free symbol files for download.
I am not going to upload free electrical drawing symbols. There are plenty of sites already out there that you can get free download from.
What I will do is teach the beginners how to read those electrical symbols from the design drawings or whatever drawings you happen to be involved in. If you are an office manager and you need to understand the electrical single line diagrams for your three-storey office and you don’t know how, then you have come to the right place.
If you plan to start a career as a construction electrician, you have also come to the right place. As a construction electrician, you will need the ability to interpret specifications, electrical drawings and sketches. Before you can interpret the drawings and sketches effectively, you need to correctly understand the electrical symbols.
If you are a hobbyist and you feel that there are thousands of ‘really cool stuff’ out there which you can just assembled on your on own at the cost of just a few pennies each (if you only know how to read the electrical or electronic schematic diagrams), then you also have come to the right place.
So if you are a beginner to electrical drawings and electrical symbols, you have come to the right place. I did not say that because the things that I will present on this blog will be easy, but because I have been working with electrical symbols and electrical drawings for twenty-five years.
As I gradually build this blog, I will increase the complexity of the materials and the examples that I will use. Therefore, those of you who feel that the house electrical symbols presented here are ‘chicken feet’, come back again after two or three months. You should have some things interesting enough for you to read by then.
B. Why I choose house electrical symbols
Why do I choose the house electrical symbols? Because that is one of the simplest electrical installations that everyone still alive can relate to in her daily life. No matter what your background is, you can see what I show here immediately in your house.
The number of electrical symbols used in house electrical drawings is also quite limited. You can get a reasonable understanding of the electrical system in a reasonably short time and you do not have to learn much technical stuff for that.
I have also chosen the house electrical symbols as my first topic for another (more important) reason. As a construction man in the electrical field for so long, I have always been very concerned on electrical safety. So many people die each year because of electrocution and I do not like that. So I always try to ‘preach’ this matter in whatever I do.
Basics of electrical engineering can be overwhelming to some people. Some just do not have enough spare time to learn, even though they fully understand that some knowledge of a few electrical basics and skills can mean between life and death of electrocution to their loved ones.
So I present to you the following two diagrams and a schedule of symbols and legends. These three will help you understand what a house electrical installation is.
Do not be deceived by the simplicity of the small installation represented by these drawings. A huge bungalow with twenty rooms, or a three-storey office, will be just as easy to understand once you understand the few symbols in the electrical drawings for this two-bedroom single-unit house.
And yes, I will actually be sending a few posts on electrical drawings and symbols for bungalows and other types of high-end residential houses in future.
C. Background of the example electrical drawings
The design is actually an old design for single unit teacher’s quarters in rural areas. It has been used for more than forty years throughout this country. Thousands of units have been electrified with this design and quite a number of them are still in use today in certain parts of the country.
Of course, throughout this period, many have been upgraded and new wiring put into place. However, they still use the same basic design and those drawings they use for the electrical installations still utilize the same symbols.
The design was done during the time when the electricity was a new way of life for the people here. The electricity was generally used for just a few basic purposes. That is why you see the number of socket outlets provided is minimal.
You may also be surprised to see that the lighting was barely enough by our today standard.I have replaced some components with the actual components that you actually find in your house electrical panel today. Forty years ago the 6 Amps MCB was not available yet. The engineers and electricians used fuses. They worked just fine, but the MCBs (miniature circuit breakers) are better and they do not have to be replaced after each time a circuit trips.Now let’s begin the lesson.
D. What is on the drawings
Refer to the three drawings below while you are reading this. Remember that these three diagrams must actually be read together. Drawing 1 Picture 7 shows the basic house layout. A real house will have more than what is shown in this drawing, I agree.
However, we only put inside an electrical drawing those symbols that are meant to help give the meaning to the electrical information that the drawing is supposed to convey. If a room’s purpose is adequately explained by just having its room name, then only the room name is shown inside the room in the drawing. Architectural information (and therefore architectural symbols or building structural symbols) can be referred to in the architect’s or the structural engineer’s drawings.
Even on big projects with the cost of electrical installation amounting to millions of dollars, it is still the standard approach to the electrical layout drawings. If unnecessary information (and therefore the unnecessary legends and symbols) and details are also shown, they will contribute to the actual number of errors that happen during the actual installation of the electrical works.
Drawing 1 – Electrical layout drawing for a small house electrical installation
This house have a few basic spaces (See Drawing 1):
a) Starting from outside at the main entrance, you have the car porch. That’s also part of the house space that needs electricity.
b) At the car porch you also have the electric meter panel, which belongs to the electric supply authority or the electric supply company licensed by the government to supply and sell electricity to the public in that area.
Electric meter symbol
c) Do you know where this meter panel is on the electrical layout drawing? If you are not sure, then that is the very reason you need to learn about electrical symbols and how to interpret information on the electrical drawings.
d) Now let’s go step by step. In Drawing 2, you can see a list of electrical symbols with a little description for each one of them. At the bottom of the list is the energy meter symbol (symbol No. 10). Going back to Drawing 1, you can see the same meter symbol at the house entrance to the left of the front door, right on the house front wall. You saw this meter inside Picture 1 and Picture 2 below. Of course it is not the same house, but the location of the meter is exactly the same. The height of the meter is a well above a level reachable by hand to place it out of reach.
e) Now you have seen the meter symbol in the list of symbols (Drawing 2). You have located the meter at the front door inside the electrical installation layout drawing (Drawing 1). You have also seen the actual photo pictures of the meter at a similar location in Picture 1 and Picture 2. I am quite sure you have actually seen these types of meters before with your own eyes somewhere even if your house does not have one.
However, it is Drawing 3 that will set you on the path to the electrician’s world. That is the picture of electrical schematic diagram, or some will call it ‘electrical single line diagram’ or ‘electrical one line diagram’.
f) Together with the symbols on the electrical layout drawing, the schematic diagram drawing lays out the overall system for the whole electrical installation. As to the kWh meter we just talked about, it is one of the high profile parts in the schematic.
g) Locate the meter at the bottom part of the diagram. Observe that the symbol used in this diagram is not the same as that in the electrical layout drawing. Why? Because the function and the nature of schematic drawings make it impractical most of the time to use the same symbol.
You are right. We then need to make a separate list of symbols for the schematic diagram. That is actually a standard practice for many installations like the power station, control circuits, etc. However, for simple buildings and for houses, it is quite rare to have the list of symbols for the schematics. But it is absolutely alright to use one.h) Still at the car porch, you can see the blue colored fluorescent light symbol with the red colored number 1 next to it. This is one of the standard electrical symbols widely used for fluorescent lighting. Refer to the symbol list (symbol No. 2) for a brief description of the symbol. The description says “2 feet fluorescent light fixture, with one no of 18 Watt tube, ceiling mounted type.”
What the description does not say is that the light fixture is also a bare channel type, which means it does not have any diffuser to envelope the fluorescent tube. You can see the tube of the light fitting, which may not be aesthetically very pleasing in some people’s opinion. However, this type of light fixture is very efficient in terms of the lighting lumens for every watt of electric energy consumed.
i) The red colored number 1 next to the light symbol is the circuit number. It is the identification number of which outgoing circuit breaker the lighting wiring is connected to in the electrical panel (i.e. the consumer unit, C.U.). Refer to the schematic diagram (Drawing 3).
j) While you are on the schematic drawing, let me just explain a few items related to the lighting symbol and its wiring circuit number. The large rectangle with “Consumer Panel” label is a representation of the electrical panel or the house consumer unit. This rectangle is also another form of standard symbols.
In some countries, the board is also called the distribution board or the electrical DB. All components located inside the rectangle symbol are the components actually mounted inside the panel (you can see the panel picture again in Picture 3 below). While the lines shown connecting to the rectangle box are the electrical connections to the conducting parts of the panel. If it is shown as connecting to one of the components inside the panel, then an electrical connection is made to that particular component whether by cables, wires or other electrical conductors such as the earthing copper tape.
For example, look at the lower right corner of the consumer panel rectangle. You can see a symbol with the letters “6 KA” next to it. That is the grounding electrical symbol with a connecting wire symbol. The connecting wire connects the electrical grounding to the electrical panel with a wire or other acceptable earthing conductor. The point where the wire symbol connects to the rectangle is actually in itself a connection symbol or a bonding symbol.
Sometimes this connection symbol has dark black circle at the lines intersection to emphasize the need for a good electrical bonding. However, for some reasons this is not a standard practice in ordinary buildings wiring work.
k) Let’s just spend a few minutes on the schematic diagram to understand the system of the house electrical system, and how to understand the schematic drawing.
Look at the bottom part of the picture. The line coming up from the bottom has been labeled “AUTHORITY’S INCOMING LV CABLE”. This is where the system starts. The incoming supply cable may be running on electric pole as in Picture 1, or it may be underground cables. Whichever it is, that is what the line represents.
l) The line connects to the cutout fuse symbol on the meter panel rectangle. Again all components inside the rectangle are actually mounted on the meter panel. Altogether there are three components: the kWh meter, the cutout fuse and the neutral link.
You may notice that the neutral link symbol is shown without connection. This is another aspect of the electrical schematic diagram that often confuses beginners. The electrical schematic is actually a single line diagram. It does not intend to show all the actual wires or cables. A line only represents the direction of flows of the electrical power, or the flow of a certain type of electrical current.
Therefore, the line connecting to the cutout fuse shows the electric power flow from the supply authority’s cables to the house meter panel, terminating at the cutout fuse. The neutral link symbol is often shown on the drawing to show that the fuse is only installed at the phase wire. The neutral wire is only provided with solid connection, not a fuse.
So when there’s a certain fault current condition that cause the cutout fuse to blow, then only the phase wire connection is broken. The neutral connection will still be present as normal. This method of drawing is also meant to show clearly the type of supply that is delivered to the house. In this case, it is a single phase, two-wire supply.
From this angle, the neutral link is meant to show the neutral symbol, and the cutout fuse as the phase symbol. Remember that there are single phase, two-wire plus earth type of supply from the authority. This type has a 3-wire cable instead of 2-wire that we have here. The third wire is the earth wire. I will talk more about the third wire in my future posts.
m) From the cutout fuse, the power flows to the meter unit on the same panel, and then leaves the meter panel via an external cable to the consumer electrical panel, terminating at the 60-Amps switch fuse unit. The connection from the meter to the switch fuse is shown by a line (Note: A line like this can also mean a connection symbol or a cable symbol.), which generally shows a power flow connection. It can mean an armored 3-core cable, or two cheap PVC-type cables or just a simple copper tape conductor connection. More detail information on the connection is usually provided by the labels that have been provided somewhere near the symbol.
In this case, a label “2-25 SQmm PVC/PVC IN CONCEALED CONDUIT” has been provided. That label is saying that the power connection is made by two lengths of single-core PVC-insulated, PVC-sheathed cable, and the cables are installed inside a conduit that should be concealed.
Concealed where? Well, that is for the electrical contractor to solve. As far as the design is concerned, the conduit carrying the PVC cables must be concealed. It can be inside the house brick wall, or the contractor may just hide it above the ceiling. Or a combination of both methods.
n) From the switch fuse unit, the power flows to the ELCB or the earth leakage circuit breaker. The ELCB symbol may seem very simple, but inside it the component is a system by itself. This device is not explicitly shown on the electrical layout drawing. It is part of the electrical panel just like the switch fuse and the outgoing MCB (miniature circuit breakers). You can read more on how the ELCB works in my future posts on electrical shock protection. However, I have included here the typical schematic construction of the ELCB for your easy reference (Drawing 4).
o) A small note on the typical ELCB schematic in Drawing 4: Observe and study a few other electrical symbols in the picture that are not available in the electrical schematic diagram and the electrical layout drawing: the load symbol (at the right side of the drawing); the fault symbol (inside the load symbol); another type of breaker symbols (the trip circuit breaker symbol on the left); the neutral symbol and the phase symbol (at the supply side on the left); the test pushbutton switch symbol, the trip coil symbol and the search coil symbol. Observe also another type of grounding symbol at below the load symbol.
p) Note that the trip circuit breaker symbol looks like a combination of a switch symbol and the trip coil symbol. I will explain more about this on other posts. With all these symbols inside the ELCB circuit, you can safely say that the ELCB symbol is a circuit symbol, an electrical sub-system by itself.
q) From the ELCB the power flows to the busbars (the horizontal lines are actually the busbar symbols) to be distributed to individual outgoing circuits. Each of the outgoing circuits is protected by a 6A SPN MCB or a 20A SPN MCB (miniature circuit breaker). Each of the outgoing circuits has also been given an identification tag, represented by the numbers 1 to 6 in side a small circle at the end of each outgoing lines. This is the number next to the 18W fluorescent lighting symbol at the car porch in the electrical layout drawing.
So when you look at the layout drawing you know from which circuit breaker the supply is taken inside the electrical panel. This way a repair electrician knows exactly how to troubleshoot without wasting too much time. During a new installation work, the installation electrician knows exactly how the electrical designer wants the wiring to be done.
This is very important because different buildings may have different functions that will affect how the electrical system is to be wired. With this method of conveying the requirements to the electrician or the contractor, the owner of the building or the installation will get exactly what she pays for.
r) Notice that next to each circuit identification number on the schematic drawing a brief description is given to describe briefly all the loads connected to that circuit. Again in the case of outgoing circuit no. 1 above, you can see that “3 NOS 1 x 36W (F) & 1 NO 1 x 18W (F) & 2 NOS C/FAN” is connected to this circuit.
With this information, it can be quickly checked whether the wiring cable size to supply total loads is adequate. The cable size itself is also clearly shown there with the labels and the tag lines. In this case our 18W fluorescent circuit is wired with 2 PVC-insulated wires of 1.5 square millimeter in side a metal conduit and all metal parts of the light fixture are connected to earth by a third wire of the same type and size. So at least 3 wires will be connected to this fixture. That is what is meant by the label “2-1.5sqmm PVC + 1-1.5sqmm E IN G.I. CONDUIT” next to the wiring symbol.
s) With that you now understand the electric power flow, also the parts and component information that the schematic drawing intends to convey. Before I close this paragraph, one more thing I need to highlight.
Look at the schematic again and observe that there seem to be two busbar symbols supplying current to the circuit breaker symbols, and the second busbar are connected through a second ELCB. Notice also that the labels given to both ELCB symbols are almost same - 60A DP (100 MA) – with a minor difference – the second ELCB has “(30 MA)” label instead of “(100 MA)”. What it says is that both ELCBs are rated at 60A, and both are two-pole type (the DP label is a double pole symbol, the two pole symbol, or 2 pole symbol).
However, the first ELCB has its sensitivity to earth leakage current set at 100 miliamperes, while the second ELCB is set at 30 miliamperes.
t) Why? I am sure this “why” has so many branch questions inside the big one, and if I go further it will develop into another big topic that will distract us from the present topic. So I will have to dedicate a separate post in the future for it.
For now just observe that the second ELCB symbol actually feed currents to circuits supplying only the socket outlets. All13A power sockets in the house are supplied from this busbar and given a more sensitive (therefore better) shock protection setting.
The first ELCB on the other hand feeds power to all other electrical fittings and fixtures including the lighting and the fans. If you install a 4 kW water heater to the house toilet, it should also be supplied from the 100 mA ELCB, and never from the 30mA one. This is actually a deeper issue on electric shock protection. I will send one or two posts on the house electric shock protection and which symbols on the electrical drawings take on this critical safety function.
u) Now let us go back to the electrical layout drawing (Drawing 1). We were talking about the two-feet ceiling mounted bare channel 18W fluorescent light fixture at the car porch when we left for the schematic diagram. I am not yet done with this light fitting because there one last piece of information I have not yet explained related to this fitting, which is the red dotted line with arrow symbol coming horizontally from the 18W light symbol, and turns 90 degree towards the main door. This is actually a wiring symbol for the light fitting and the arrow actually points to the direction of the control switch for that light.
In this case, the switch is located on the wall just inside the main door. The switch symbol is in blue color near the red colored consumer electrical panel. Refer to symbol No. 7 in Drawing 2 for a better view of the switch symbol and the brief description.
v) Notice also the speed regulator and switch symbol for the ceiling fan just next to the light switch on the wall. As you observe the location of the electrical symbols on the layout, you will gradually understand and rationalize yourself how they are laid out.
One last item I wish to touch on the layout drawing is the socket outlet symbols. Notice how they are laid out and the circuit number of the circuit that are feeding them (Recall the outgoing circuit number on the schematic diagram). Take note that for the 20A circuit breakers used in this design, two 13A socket outlets are the maximum number that can be connected to each of the circuit breakers. While in the case of the 5A circuit breakers for the lighting and ceiling fans, each circuit breaker can handle up to ten lighting and ceiling fan points per circuit.
w) Now you already know what those symbols on the electrical drawings mean. If you go from symbol to symbol on the schematic drawing and try to relate them to the symbols laid out on the electrical layout drawing, you will have the overall full picture of the typical electrical installation for a simple house like the one illustrated by these drawings.
Drawing 2 – Legends and symbols for electrical installation drawings.
Drawing 3 – Wiring schematic drawing
Drawing 4 – ELCB circuit
Picture 1 - Incoming electricity supply cables on concrete poles
Picture 2 - Supply authority's meter panel at house entrance or main door
Picture 3 - Home electrical panel
I have to switch off now. In my future posts I will give more explanation on each of the symbols. That will be useful for readers who wish to understand deeper into the electrical drawings, and to those with the intention of getting their hands wet into the electrical fields.
E. Note of caution: ELECTRICITY IS DANGEROUS. IT KILLS.
One last note of caution for the readers who are already feeling excited with this newfound knowledge: Electricity is dangerous. It can kill, it does kill and it will always kill.
Any knowledge in this world is useful but some knowledge need hands-on skills before it can be mastered. However, some types of hands-on skills are very hazardous to learn.
Before you can get your hands wet in electrical wiring works, you first need to know enough to keep yourself safe in the learning process.
Until you know that you will be safe doing this or trying that, keep reading and observing. The time will come when you are sure that you already know enough to try a little bit yourself.
Be safe and stay safe.
See you soon.
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