Looking for more explanation of testing

[OtleySpark]

I've recently completed my Domestic Electricians course but would like to find a good book that didn't just tell me what I should do (especially in the testing/inspection area) but why I am doing it.

We were shown how to test for all sorts of things and fill in the forms (prospective fault current, earth fault loop impedance, etc) but not why.

So does anyone know of a good book that explains these things?

Thanks

 

[ricicle]

Try IET Guidance Note 3

 

[ban-all-sheds]

The Part P Doctor books are good for that.

 

[JohnW2]

I've recently completed my Domestic Electricians course but would like to find a good book that didn't just tell me what I should do (especially in the testing/inspection area) but why I am doing it. We were shown how to test for all sorts of things and fill in the forms (prospective fault current, earth fault loop impedance, etc) but not why.

You are right to be concerned, and it's rather frightening that such a course fails to teach why the tests are done. What really seems to be missing in so many courses is thorough teaching of the underlying basic electrical principles. If someone has a good understanding of those principles, then the reason for (and mechanism of) the testing would probably be fairly obvious. The books that have so far been suggested to you are good, but I'm not sure to what exent they will help you to understand the 'why'.

Kind Regards, John

 

[OtleySpark]

I've recently completed my Domestic Electricians course but would like to find a good book that didn't just tell me what I should do (especially in the testing/inspection area) but why I am doing it. We were shown how to test for all sorts of things and fill in the forms (prospective fault current, earth fault loop impedance, etc) but not why.

You are right to be concerned, and it's rather frightening that such a course fails to teach why the tests are done. What really seems to be missing in so many courses is thorough teaching of the underlying basic electrical principles. If someone has a good understanding of those principles, then the reason for (and mechanism of) the testing would probably be fairly obvious. The books that have so far been suggested to you are good, but I'm not sure to what exent they will help you to understand the 'why'.

Kind Regards, John

Yes, too many of the books I've seen are like dictionaries, they explain all the tests but don't tell you the significance or meaning of the results in relation to everything else.

I'll have a look at those suggested above, thanks.

 

[Taylortwocities]

Us 'old school' sparks are used to learning being done the other way round.

The way it used to be taught is to learn about the why first -
then the how and when.

That's one of the scary things about the DI short courses. And not your fault, its the way the world is....

You'll understand why the 5WW mentality gets a hard time here and elsewhere.

But PLEASE come back and ask, any time.
Most of us won't give you a hard time.

 

[JohnW2]

Us 'old school' sparks are used to learning being done the other way round. The way it used to be taught is to learn about the why first - then the how and when.

Exactly. As I said, it should all start with a thorough understanding of the underlying principles. Not only is that desirable, and makes sense, but it actually means that a lot of the 'how and when' then hardly needs teaching, because it is 'obvious' to someone with the background knowledge.

That's one of the scary things about the DI short courses. And not your fault, its the way the world is....

Indeed - and, of course, it's by no means unique to things electrical. Parallels exist in an awful lot of other trades and professions. In many contexts, the concept of having 'lesser trained/qualified' people to perform some tasks does makes some sense, since 'fully/properly-trained people' may be 'unecessarily/over-qualified' for some things. However, when it's done properly, there is considerable resistriction and regulation of what this 'lower tier' can do, and they are properly trained in relation to their restricted repertoire of activities.

Kind Regards, John

 

[securespark]

Most of us won't give you a hard time.

 

[ericmark]

I will admit there were many things I did without really knowing why. It was not until I did my degree did I understand the why for some of it.

We have questioned on this forum the loop impedance readings what they did in the past with the earth loop impedance was to ensure if there is a direct short to earth enough current can flow to ensure the magnetic part of the MCB will trip.

So for example a B32 MCB need 5 times rated current (B) to trip the magnetic part so 160 amp. Ohms law 230/160 = approx 1.44 ohms and that is the figure given in the book.

However with RCD that is not really required but we also have volt drop and from the loop impedance (line - neutral) we can calculate what the volt drop would be with a set load. This is of course total and we are only worried about after the DNO head.

The prospective fault current should be measured twice once to earth and once to neutral some meters auto select neutral when on prospective fault current and earth when on earth loop impedance others need you to make up leads or use probes.

As well as the volt drop we also look for the rating of the protective device. A RCBO often rated at 4.7kA and MCB at 10kA and we are looking to see if this will be exceeded with the prospective fault current. However there is also the let through value of the DNO fuse which since this is less than 4.7kA for the 100A domestic supply I suppose we don't really need to test but of course with commercial premises one has much more than a 100A supply and I had a tower crane where I had to use fuses instead of a MCB to supply the radio charger as the prospective fault current was so high but unlikely to get this with domestic.

I did try and get my head around the let-through value of a fuse and moulded breaker but when it came down to the on site work I found the resistance of the fuse reduced the prospective fault current to a point where the let through value was no longer an issue.

When I first finished my apprenticeship we did very little testing if we had a insulation tester that was about it. As we started to fill in installation certificates I took the readings and filled in the form without really understanding not only what the measurement was taken for but what was the pass limit. I then took my course and C&G2391 exam when I at last understood the why. I looked back with dismay when I realised how many installations I must have filled in paperwork showing they were not compliant. This was around 1992 and I had been working on designing my own installations for around 20 years.

Of course when I started there were no MCB's and although there is a limit with a fuse it is not as critical as with the MCB.

As to a book explaining why the ones I have now read are not light reading and the maths is complex. So without a lecturer to explain I don't think they would help. Thévenin's theorem and Norton's theorem as you do them does explain but I did not do these until I went to University not sure if now done in college at level 3 but they were not done at the time I went to college at least by my college.

Although today we have national qualifications when I went to college many of the exams were internal set or local set in my case Welsh Board so if the lecturer did not understand he just did not teach it. Many were ex-miners where I lived teaching because of some accident in the mine or because the mine had closed. I now realise how poor my education was but at the time I had no idea I was doing anything wrong.

So full marks for asking the questions.

 

[PrenticeBoyofDerry]

I've recently completed my Domestic Electricians course but would like to find a good book that didn't just tell me what I should do (especially in the testing/inspection area) but why I am doing it.

We were shown how to test for all sorts of things and fill in the forms (prospective fault current, earth fault loop impedance, etc) but not why.

So does anyone know of a good book that explains these things?

I think I have already linked you this publication in previous post, it is you a good overview, with valued information on inspection. testing and certification.
Shows in easy steps (with helpful pictures) how to perform the tests, backed up with some, easy to follow calculation. It also gives helpful information in the filling of certificates. There are a few exercises that you can carry out, to test you understanding.
There is no substitute for supervised on-site experience but to someone who is looking for a little help in the understand via a reference book, I recommend it highly.
Practical Guide
Also there is some information here that may help, some of the information does need updating to 17th, mainly IR test values and the lack of RCD testing. But good free information.
http://www.tlc-direct.co.uk/Book/8.1.1.htm