Tuesday, October 27, 2009

Home electrical earth installation

This post is about home electrical earth installation or home electrical grounding. Some people call it electrical ground, or earth grounding, electrical earth, or just grounding or ground. In fact, I have come into some really funny names for the electrical earth.

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That is because the earth has no mass, and it has no quantity. It is actually a function. An electrical current has no mass, but it has a quantity. Your house switched socket outlet is rated 13A, for example. That is 13 Amperes, a quantity that is definite and measurable. The more enlightened ones will say that is the quantity of electrons that is measured.

Unlike current, many people seem to have given up trying to understand this electrical earth, never mind those who never care in the first place.

Whatever the real reasons are, this situation has resulted in a very serious problem: many people are not able to use electricity safely. They allow their loved ones be exposed to unnecessary risks and dangers.

Look at the nice diagrams that I quickly prepared for you below. Picture No 1 is how the small house looks like at the cross section view from the right side of the house. Note that the main entrance is on the left side of the drawing. Picture No 2 is the house electrical layout. I used the same picture (plus a little additional information which I hope you can figure out on your own – this is the kind of materials that nowadays they put inside the books on urban survival skills) in the earlier post to explain on how to read the house electrical wiring, the electrical symbols used, and a simple guide on how to check your house electrical installation from safety view point.

Picture No 3 is something I cooked up to show you an overall view of the electrical system involved in the flow of electricity from the substation to your house. This diagram is very important for those who do not have the time to think about technical stuff on electrical system, but have been very concerned about the risk of electrical shock that may be present in their house. Take your time to study this diagram. It is actually nothing more than a flow chart actually.

While Picture No 4 contains some additional details about “the earth” for your house wiring. This is the earth chamber. This is the part that help the wiring discharge the current to where it belongs when some malfunction occurs to the wiring or the appliances so your house occupants can stay safe. You may have seen this at your house, but only the top part on the surface is visible. So now you can know how it looks inside and underneath.

Please note also that the lightning protection also use the same thing to discharge the lightning current during the lightning strikes. Sometimes it is called the lightning rod. So your house usually has at least two of these earth chambers: one for the electrical and one for the lightning protection system.

That is the short brief about the pictures that I have uploaded to help you to understand what the electrical earth is.

Now let us start the main lesson. I put all the four images first and the explanation after them.

Picture No 1 – Incoming supply and earth chambers

Picture No 2 – Electrical layout drawing

Picture No 3 – Fault current path

Picture No 4 – Details of the earth chamber

1. Home electrical basics

We need the earth installation because we have electricity in our house. So we must understand the home electrics first before we can really understand the earth. You can visit this post, Home electrical wiring, symbols and checking, to read more details of this subject.

Picture 1 shows how the electric supply is brought to the house. It came from a substation somewhere and transported through cables to your house. Here it came through the overhead cables tied to the top of electric poles along the street of the residential area. I am sure most of us have seen this and how the cables are brought to the energy meter at the front wall of the house. Anyone who haven’t seen it can see the pictures of them somewhere else in this blog.

Now look at Picture 3. The source of the electricity is at the substation on the far left of the picture while location where it is being utilized is on the far right. If you see the pretty girl then you can see that she was being electrocuted. That what we all don’t want and that is why you need to watch the diagram carefully. I will not write too long today because it’s already 1.00 AM and I have to go to work tomorrow. However I will update this post and write some more details. By the time I am finished with this post (after a few updates probably) you will understand enough to take the necessary care and precautions at home with regards to electricity and electrical appliances.

For now just observe that the electric current from the power transformer at the substation flows along the path indicated by the direction of the red arrows pointing to the right side of the diagram. When it arrives at the four circuit breakers on the electrical panel, it travels through the lowest circuit breaker because that is the circuit that is supplying the socket out where the washing is connected. Normally the current travel back to the star point of the transformer through the second wire which is the lower black line from the washing machine. I did not put any arrow to indicate the return path of the current. But that path will go to the neutral busbar (the one with the label “E” inside the electrical panel). If you trace the connection, it will go back to the neutral point of the power transformer.

But the diagram shows that there is another two alternative paths the current can take to go back to the transformer star point. The first (or the second because the first is through the neutral wire) is shown by the red arrow right below the washing machine. You can see the black line connecting to the machine’s metal body. The connection is shown here by the black dot at the intersection point.

So the current can travel through the earth wire shown by the red lines as I said above. This is actually the third wire in your house wiring, which is the green wire. If your house wiring is concealed inside the wall, you may have seen the green wire inside the extension cord or at a damaged plug where the cover has been broke. That is the third wire shown by the red line below the washing machine. This path will follow the wire and arrive at the earth busbar (with the label “E”) inside the electrical panel or distribution board. This earth busbar is located near the neutral busbar (label N).

If the neutral busbar is connected to the transformer star point through the neutral return wire, the earth busbar is connected to the earth camber that I mention at the beginning of this post (see Picture 4). The black wire labeled “Electrical panel earthing” is what we called a grounding conductor or the earth conductor. With this earth conductor the machine is solidly connected to earth. Yes, connected to the real earth mass. The earth chamber is just an enclosure and a cover to protect the components inside and underneath it which are a long copper rod with some very important connection accessories inside.

Back to the ground wire path. Under normal situation the electric current inside the washing machine does not flow through this path (the third path). It will just flow through the neutral wire to flow back to the transformer star point. However like everything else in life, nothing last forever. The most expensive machine that you can buy may have a five year warranty sticker on it and the vendor’s office guaranteed that you will have their best technician knocking your house door within 15 minutes of your call.

However the girl in the diagram may not be alive long enough to make the call. The line from the black dot below the machine to the earth busbar follows such a zigzag route. I could have made it straight and direct, but I didn’t. Some of you may have a pretty good idea why. I may need one whole post just to explain the “why”.

Okay, so nothing last forever. One day one of the components and parts inside the machine will fail. If the failure leads to poor insulation of live parts, then a small amount of electric current may leak to one of the exposed metal parts of the machine. That metal part will get energized or “live”. This is why we need the earth wire connection there. The exposed metal parts are not supposed to get “live”. That’s why they are exposed to touch. So the voltage they carry due to the leaked current cannot go back to the neutral star point through the earth wire. With the earth wire, that voltage has a path to escape to which is straight to earth.

So what? The metal part gets energized and it has the current flowing through it and to earth. People will still be touching a live metal, right? Right! But that metal and the designed live metal inside the machine have a very big difference. The bonded exposed metal is at the same potential as the earth which is 0 volt (that is “zero volts”). And the girl there is also at zero volt, the potential of the earth. Since both the girl and the exposed metal are at same potential, the current will not flow through the girl, or the flow will extremely small. (That is in theory. Many other factors are also involved in real situation).

The above is point no 1. Another point is the solid connection will minimize the resistance between the exposed metal to earth. Since the current is inversely proportional to resistance, a minimum resistance will give maximum current. This aspect is utilized by our ancestors to create a protection device that can protect the girl. The leaked current will be detected by the devise and it trips the connection of the supply to the machine. Therefore the will be saved before the voltage rise up high enough to cause serious injuries. The established setting of this current has been 30 mili-Amperes. This is what the experts in this field have come to follow, and this is the label that you can see near the earth leakage protection devise in Picture No 3.

Which devise? That is the ELCB (earth leakage circuit breaker). It’s in side the electrical panel. On the diagram also it is labeled “ELCB”, with “60A DP” and “(30 mA)” label just below it.

The ELCB itself is a long topic so I will save it for another time. But if you cannot wait, my earlier posts have already some information on how it works. I will explain more in future posts. (UPDATE: Visit ELCB - Home Electrical Shock Protection and also ELCB circuit for a much more detailed information about the ELCB circuit breakers.)

So now do you understand why we need the electrical earth there? Why having it properly working is an absolute necessity? A matter of life and death? Good.

I have not forgotten that I titled the post “Electrical earth installation”. And I have not even started the installation part of it. I was absorbed in the why. The how part of it will have to wait for another time. I will continue on this topic as an update to this post. There will be other posts on the earth installations, but I also need to make this post complete as what the title says. Some readers may not have the time or desire to click to another post to get to what they hope to find.

See you soon.

Note: Visit this post, Free electric installation picture, to see more pictures, diagrams and drawings of electrical installations. I started it some time back as an anchor post, but got around to really finish it. It can be much faster than searching through the BLOG ARCHIVE folder.

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2 comments:

Anonymous said...

Which countries does your info realte to? I like the way you explain things, I have difficulty understanading basic electrical stuff and have set a goal to know how and why it works particularly re safety.

Mick

Edwin Sander said...

Great article, I'm sure that I will need an electrical services like these Adelaide electrical contractors that I found on this website. They have a great service offered for their clients and you can also visit them if you have an electrical concern.