One area that always created a stumbling block was in remembering earthing arrangements since at the time the lettering did not create links. Using Tony Buzan's books however I have found that I can remember these by producing mind links.
In Latin earth is called Terra (Terre in French ) so we get Terra Firma, on solid ground.
So the first letter denotes if the supply is connected to Earth or Terra with the capital letter T. If insulated from earth then I is used, I for insulated.
The second letter denotes where the consumers earth is connected to. So T would indicate to earth. So TT means that the supply transformer star point is connected to earth and the consumers equipment is also connected to earth using earth spikes etc.
In an IT system the supply transfomer has no connection to earth but the consumers equipment is connected to earth using earthing spikes etc.
N stands for neutral and thus in a TN system the consumers earth is connected to earth via the neutral of the supply.
TN‑S is where the earth and neutral are fed back to the supplier with seperate conductors.
TN‑C is where the earth and neutral are fed back to the supplier using one conductor.
TN-C-S is where the earth and neutral are fed back to the supplier using one conductor but this time the connection of the earth to the neutral is not directly made at the consumers end thus there are two seperate conductors from the premises.
There is good article on this in pdf format form the IEE
Monday, 25 June 2007
BS 7671 and City & Guilds 2391
Still have not took the course or the exam yet but still looking round for snippets of information that could appear on the paper.
A lighting circuit fed with a 6Amp MCB keeps tripping when attempting to do measure prospective fault current.
You would expect the MCB to sometimes trip since the current used to measure prospective fault current is much higher. From memory I seem to remember a figure of 25Amps. One source suggested that you could bridge the MCB out. If you did and at that very instant you turned on the main isolator a fault occured on the lighting circuit the whole lot could go up in flames since you could be feeding a 1mm csa cable with 100 Amps. Far better to measure R1+R2 and calculate. Still who am I to tell you I ain't passed yet!!!!!
A lighting circuit fed with a 6Amp MCB keeps tripping when attempting to do measure prospective fault current.
You would expect the MCB to sometimes trip since the current used to measure prospective fault current is much higher. From memory I seem to remember a figure of 25Amps. One source suggested that you could bridge the MCB out. If you did and at that very instant you turned on the main isolator a fault occured on the lighting circuit the whole lot could go up in flames since you could be feeding a 1mm csa cable with 100 Amps. Far better to measure R1+R2 and calculate. Still who am I to tell you I ain't passed yet!!!!!
Friday, 22 June 2007
2391-101 Inspection, Testing and Certification of Electrical Installations Zs Ze R1 R2
From the City & Guild Chief examiners reports it appears that many get calcultations of Zs, Ze, R1 and R2 wrong. Remember folks I have not yet taken the course or the 2391 exam.
Zs is the sum of Ze, R1 and R2 seems simple enough. Zs= Ze + (R1+R2).
Ze is the external impedance. Although you can calculate the value, it is more normal that the value is obtained by measurment using a suitable instrument or by enquiry.
R1 is the resistance of the phase conducter
R2 is the resistance of the CPC or circuit protective conducter.
In practical test situations the value of R1 + R2 is obtained in one test so could in effect be considered as one value say Rt. So the equation would become Zs = Ze + Rt.
I just hope that in the 2391 exam you are not expected to know the values allowed in BS 7671.
So why Z and R?
Z is the impedance and applies to AC circuits.
R is resistance and applies to DC circuits.
Zs is the sum of Ze, R1 and R2 seems simple enough. Zs= Ze + (R1+R2).
Ze is the external impedance. Although you can calculate the value, it is more normal that the value is obtained by measurment using a suitable instrument or by enquiry.
R1 is the resistance of the phase conducter
R2 is the resistance of the CPC or circuit protective conducter.
In practical test situations the value of R1 + R2 is obtained in one test so could in effect be considered as one value say Rt. So the equation would become Zs = Ze + Rt.
I just hope that in the 2391 exam you are not expected to know the values allowed in BS 7671.
So why Z and R?
Z is the impedance and applies to AC circuits.
R is resistance and applies to DC circuits.
2391-101 Inspection, Testing and Certification of Electrical Installations Testing of a 30mA RCD
The chief examiner for the City & Guilds mentions that many taking the examination fail on this question. Again I have not passed or taken the course but would be tempted to write my answer something like this:
Using a RCD tester that is in calibration, set the instrument to 50% of the tripping current of 30mA, namely 15mA.
Carry out the test at this current for 2 seconds during which time the RCD should not trip for each half cycle.
Set the RCD tester to 30mA (the actual tripping current) and operate the test button. Record the time in mS that the RCD took to trip. This from memory should be less than 200ms if not used as protection against indirect contact, do this for each half cycle.
Where the RCD is used for protection against indirect contact set the level to 5 times the trip current, namely 150mA. On both half cycles the time to trip should be less than 40ms.
Press the test button on the RCD to verify that this functions correctly.
Using a RCD tester that is in calibration, set the instrument to 50% of the tripping current of 30mA, namely 15mA.
Carry out the test at this current for 2 seconds during which time the RCD should not trip for each half cycle.
Set the RCD tester to 30mA (the actual tripping current) and operate the test button. Record the time in mS that the RCD took to trip. This from memory should be less than 200ms if not used as protection against indirect contact, do this for each half cycle.
Where the RCD is used for protection against indirect contact set the level to 5 times the trip current, namely 150mA. On both half cycles the time to trip should be less than 40ms.
Press the test button on the RCD to verify that this functions correctly.
2391-101 Inspection, Testing and Certification of Electrical Installations
2391-101 Inspection, Testing and Certification of Electrical Installations is according what I have read on the Internet and heard form those that have already taken the exam difficult to pass. The City and Guilds website only confirms the evidence. It would seem that less than half of those taking the exam pass.
Well it appears that I have to sit the examination, after first doing a three day course and also a one day practical. Before I commence the course I thought I would get familiar with what will be required to pass.
The chief examiner's report gives some indication as to where some easy marks can be gained.
One such area is in the sequence of testing. It makes logically sense that before power is applied to a circuit that it is tested since the testing could highlight any possible dangerous faults.
Isolate and Check was a slogan used in the mining industry. Before touching the wiring I would prove my voltage indicator, verify that the circuit or circuits are dead by testing at a few different points, once satisfied, verify that the voltage indicator still works. (Using a proving unit).
So which test comes first? Well what is the point of doing an insulation test if there in an open circuit on the phase, neutral or circuit protective conductor since any test would be meaningless. So in I am correct in my theory then the continuity of the conductors needs to be established.
For a simple circuit R1 + R2 is the phase conductor + the CPC impedance values and will be in ohms subtract from this any value for the leads that were obtained on the instrument check. The neutral should have the same csa of the phase conductor and should be almost equal to that of the phase impedance depending upon the circuit arrangement. For a three phase circuit the highest impedance is the one that could prevent a protective device operating thus this is the one used in practice against the chart to determine whether or not the reading is low enough and therfore recorded. Polarity can be checked at this point by making sure that single pole switches break the phase conductor and not the neutral or CPC.
Once continuity of all possible circuit combinations have been recorderd I would guess that each circuit is tested for insulation resistance using the 500V range of an insulation tester for domestic premises. Although the leads should be shorted together to verify the meter reads zero, I prefer to place one lead on an earth and then verify my contact by connecting the other lead to another earth location close by. Since all wiring would need to be tested it is important to have all the switches are turned on. Where there is two lighting circuits this means that all combinations of the switching needs to be verified. I doubt the exam would go beyond the simple two way circuit.
A reading of zero Megohms could indicate that a shorting wire is still in place or that there is a fault. If a low test is obtained between phase and neutral it could be that a neon is used on a fused spur or that a genuine fault is present.
If tests revealed a fault and I resolved the problem then I would begin the tests again in case during my investigations I had inadvertently disturbed the wiring.
more later, (eyes are tired)
Well it appears that I have to sit the examination, after first doing a three day course and also a one day practical. Before I commence the course I thought I would get familiar with what will be required to pass.
The chief examiner's report gives some indication as to where some easy marks can be gained.
One such area is in the sequence of testing. It makes logically sense that before power is applied to a circuit that it is tested since the testing could highlight any possible dangerous faults.
Isolate and Check was a slogan used in the mining industry. Before touching the wiring I would prove my voltage indicator, verify that the circuit or circuits are dead by testing at a few different points, once satisfied, verify that the voltage indicator still works. (Using a proving unit).
So which test comes first? Well what is the point of doing an insulation test if there in an open circuit on the phase, neutral or circuit protective conductor since any test would be meaningless. So in I am correct in my theory then the continuity of the conductors needs to be established.
For a simple circuit R1 + R2 is the phase conductor + the CPC impedance values and will be in ohms subtract from this any value for the leads that were obtained on the instrument check. The neutral should have the same csa of the phase conductor and should be almost equal to that of the phase impedance depending upon the circuit arrangement. For a three phase circuit the highest impedance is the one that could prevent a protective device operating thus this is the one used in practice against the chart to determine whether or not the reading is low enough and therfore recorded. Polarity can be checked at this point by making sure that single pole switches break the phase conductor and not the neutral or CPC.
Once continuity of all possible circuit combinations have been recorderd I would guess that each circuit is tested for insulation resistance using the 500V range of an insulation tester for domestic premises. Although the leads should be shorted together to verify the meter reads zero, I prefer to place one lead on an earth and then verify my contact by connecting the other lead to another earth location close by. Since all wiring would need to be tested it is important to have all the switches are turned on. Where there is two lighting circuits this means that all combinations of the switching needs to be verified. I doubt the exam would go beyond the simple two way circuit.
A reading of zero Megohms could indicate that a shorting wire is still in place or that there is a fault. If a low test is obtained between phase and neutral it could be that a neon is used on a fused spur or that a genuine fault is present.
If tests revealed a fault and I resolved the problem then I would begin the tests again in case during my investigations I had inadvertently disturbed the wiring.
more later, (eyes are tired)
Thursday, 21 June 2007
BS 7671 and City & Guilds 2381
Proof of knowledge of BS 7671 or the IEE 16th Edition wiring regulations are required for electricians in many UK industries. To prove you have an understanding of the regulations, you can obtain the City & Guilds Certificate 2381.
Provided that you have a good electrical background, the examination should not really pose too many problems. The examination is open book meaning that you are allowed to have for reference in the exam the IEE 16th Edition of the wiring regulations and also the IEE On-Site Guide.
Like my teacher friend says "It is more important to know where to find information rather than remembering the information". When I took my exam, I spent my revision time recounting where to find the information in the books. (I past by the way).
Do you need additional books to help you pass? If you taking the examination on it's own without taking a course then I would say they may help you understand some of the more difficult parts of the regulations or to offer information into the background of why there is a need for a specific regulation.
Provided that you have a good electrical background, the examination should not really pose too many problems. The examination is open book meaning that you are allowed to have for reference in the exam the IEE 16th Edition of the wiring regulations and also the IEE On-Site Guide.
Like my teacher friend says "It is more important to know where to find information rather than remembering the information". When I took my exam, I spent my revision time recounting where to find the information in the books. (I past by the way).
Do you need additional books to help you pass? If you taking the examination on it's own without taking a course then I would say they may help you understand some of the more difficult parts of the regulations or to offer information into the background of why there is a need for a specific regulation.
Electricity At Work Regulations EAWR
Electricity At Work Regulations (EAWR)
These came into force in 1989, yet it would appear that many people are unaware of their duties under the act.
In a normal court of law a person is considered innocent unless the prosecution can prove guilt. With Health and Safety issues a person is guilty until they prove themselves innocent. At college one particular lecturer would constantly remind us that if someone died we could be doing a stretch of 10 years for manslaughter if proven guilty.
The EAWR is a statutory document, meaning that it is written law and thus contravening it means that you could be prosecuted. Like all law, the EAWR written in such a manner that Joe Blogs on the street could not tell what it means, but to lawyers it is clear and precise with no ambiguity.
There is a fundamental law that is always used and that is that ignorance of the law is no proof of defence. So if you did not know about the EAWR, tough luck mate, you could still be facing a manslaughter charge if you breached the EAWR.
So the EAWR is written for lawyers to understand and yet you can be prosecuted for contravening the regulations, does not seem very fair does it?
The Institute of Electrical Engineers IEE also publishes regulations which are not statutory, the latest being the 16th Edition IEE Wiring Regulations (The 17th Edition is due to be published soon). The 16th Edition IEE Wiring Regulations is now a British Standard (BS 7671).
BS7671 is written to go some way to actually offering practical advice in how to comply with the EAWR. If you follow the regulations set out in BS 7671 then you are less likely to find yourself in court for breaching the EAWR. Remember I earlier that in Health and Safety matters you are guilty until proven innocent. The police collect evidence in order that the prosecution can prove that a person is innocent, well since you need to prove your innocence so you need evidence also. BS7671 comes to your assistance by setting out different documentation that when completed can prove that you have exercised your duties.
I hope that the information above as shown how BS7671 compliance can prevent you from perhaps going to prison for 10 years. Look out for additional posting in the near future with respect to the EAWR and BS 7671.
Saturday, 16 June 2007
Memory and Tony Buzan
Earlier this week I attended a course on electrical testing and from this it was decided to go and take a City and Guilds Certificate in Inspection and Testing. Roger was a little worried about the prospect of remembering all the things that could be in the written exam. I told him there is a little secret to remembering and that these can be found in books by Tony Buzan.
Master Your Memory is on sale at Amazon for £6.39 is the first book I would get and then work through the book and try it out for yourself. I can still recount the story that places the planets in order from the Sun and not only that but also in relative size to each other.
Jim was going to take a degree and I mentioned about mind maps, when he got to university on the first day, one of his lecturers said "If you do not know about mind maps I suggest you begin by finding out". Jim had already got the books and had the basics. Tony Buzan also has a book called The Ultimate Book of Mind Maps which is £8.99 from Amazon. I have not read this one but have an older book. Traditionally, note taking for revision was done in a linear format. However Tony's work shows that the mind does not store data in a linear fashion but rather in the form of links, a bit like the WWW in that there is no organised structure. By using mind maps you bring out data from the brain and create a picture of the data. An A4 sheet of paper can have a surprising amount of data contained in a mind map.
I made a mind map of the computer revolution and was amazed at level of complexity of the map created and yet it proved easy to remember this map to use at a later date.
Let us go one further and imagine you are going to give a speech then you could write several sheets of words for the speech but you will generally have to rewrite it several times since many key points are either missing or not given in a logical sequence. With mind maps you place the salient points on it with respect to the subject to be spoken about. You can then either write out your speech or just take the mind map with you. Since you only have one sheet or two at the front of you any question from the floor requiring reiteration can easily be located and the answer returned.
Before knowing about Tony Buzan I was just getting passes in exams, then using techniques shown by Tony buzan I began to get far higher marks like credits and distinctions.
The only trouble is you have a brain that is full of stuff that does not go away. Like 0.4971 being the log of pi, the square root of 3 being 1.732 or that Ada Byron was the first computer programmer but also a druggie, Alan Turing was a homosexual that died in mystery, due to cyanide poisoning. Cyanide is contained in the pips of Apples. Apple is the name of the company began by Steve Wozniak and Steve Jobs. Snow White bit into an apple and slept until she got a kiss from a prince and the story made a hit when animated by Disney that later had Pixar to produce modern animations like Toy Story but is not Steve Job in there somewhere?
Master Your Memory is on sale at Amazon for £6.39 is the first book I would get and then work through the book and try it out for yourself. I can still recount the story that places the planets in order from the Sun and not only that but also in relative size to each other.
Jim was going to take a degree and I mentioned about mind maps, when he got to university on the first day, one of his lecturers said "If you do not know about mind maps I suggest you begin by finding out". Jim had already got the books and had the basics. Tony Buzan also has a book called The Ultimate Book of Mind Maps which is £8.99 from Amazon. I have not read this one but have an older book. Traditionally, note taking for revision was done in a linear format. However Tony's work shows that the mind does not store data in a linear fashion but rather in the form of links, a bit like the WWW in that there is no organised structure. By using mind maps you bring out data from the brain and create a picture of the data. An A4 sheet of paper can have a surprising amount of data contained in a mind map.
I made a mind map of the computer revolution and was amazed at level of complexity of the map created and yet it proved easy to remember this map to use at a later date.
Let us go one further and imagine you are going to give a speech then you could write several sheets of words for the speech but you will generally have to rewrite it several times since many key points are either missing or not given in a logical sequence. With mind maps you place the salient points on it with respect to the subject to be spoken about. You can then either write out your speech or just take the mind map with you. Since you only have one sheet or two at the front of you any question from the floor requiring reiteration can easily be located and the answer returned.
Before knowing about Tony Buzan I was just getting passes in exams, then using techniques shown by Tony buzan I began to get far higher marks like credits and distinctions.
The only trouble is you have a brain that is full of stuff that does not go away. Like 0.4971 being the log of pi, the square root of 3 being 1.732 or that Ada Byron was the first computer programmer but also a druggie, Alan Turing was a homosexual that died in mystery, due to cyanide poisoning. Cyanide is contained in the pips of Apples. Apple is the name of the company began by Steve Wozniak and Steve Jobs. Snow White bit into an apple and slept until she got a kiss from a prince and the story made a hit when animated by Disney that later had Pixar to produce modern animations like Toy Story but is not Steve Job in there somewhere?
Thursday, 7 June 2007
Car Insurance
I got a quote from my previous insurer for over £300 and that was with a 15% discount. With getting a new Mazda 6 TS2 to replace the BMW116I SE, time to compare the market. Swift Cover came up best at £188 and then with extras the price was £236 approx. Since I do not work in; entertainment, gambling, modelling & professional sports. foreign or diplomatic service. scrap, second-hand dealers & merchants, market & street traders. bailiffs, debt collectors, bodyguards or doormen. motor trade, mobile mechanics, taxi or mini-cab drivers. couriers, despatch drivers, mobile caterers, or fast food delivery means I could go with them, oh and I am not under 19 or over 75.
Wonder who will be the cheapest car insurer next year?
Wonder who will be the cheapest car insurer next year?
Alto Kew 6411150 Patio Washer
To match the Kärcher 2.640-212 T-Racer Patio Cleaning Pressure Washer Accessory you might be interested in the Alto Kew 6411150 Patio Washer . It is available from Amazon UK for £49.93 at the time of writing.
Manufacturer's Description:
"The Patio Cleaner is 6 times quicker than the use of a standard lance, avoids stripes and stops splashing onto other surfaces.
The Patio Cleaner has a counter-balanced nozzle that spins in operation widening the cleaning area of a standard nozzle by 6 times. It hovers in use making it very easy to use and keeps the spray pattern nice and flat which means a very even clean and when the patio dries there are no stripes. The cleaning hood also stops spray going onto walls and patio windows which means you don't have to clean all these areas down when you've finished the patio.
You can also pull the nozzle into the head and clean decking and fence panels without damaging the wood.
Fits all Nilfisk-ALTO and KEW models except the C100.1-5. "
Manufacturer's Description:
"The Patio Cleaner is 6 times quicker than the use of a standard lance, avoids stripes and stops splashing onto other surfaces.
The Patio Cleaner has a counter-balanced nozzle that spins in operation widening the cleaning area of a standard nozzle by 6 times. It hovers in use making it very easy to use and keeps the spray pattern nice and flat which means a very even clean and when the patio dries there are no stripes. The cleaning hood also stops spray going onto walls and patio windows which means you don't have to clean all these areas down when you've finished the patio.
You can also pull the nozzle into the head and clean decking and fence panels without damaging the wood.
Fits all Nilfisk-ALTO and KEW models except the C100.1-5. "
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