How easy is it to replace a CU/do a rewire?

[ban-all-sheds]

I thought it might be useful to have a list of questions that people who think that changing a CU or rewiring a house is a P.O.P. could be asked, hopefully to show them that it really isn't as trivial as they think.

I'll admit to a level of naivete, but surely sometimes there'll be people who'll end up taking advice to either go away and learn a lot more or get an electrician if they can see that there is a lot to know rather than think the advice is aimed at protecting a closed shop.

Anyway - here's my starter for 10 - would welcome discussion and further suggestions - my idea is that when complete I'll put the list in the Wiki and ask Admin to delete this topic to not leave a record behind. The questions should all be justifiable, and I think we should avoid a list so long that it looks like deliberate obfuscation.

1. What are the 3 different types of domestic single-phase supplies provided in this country, how would you recognise them, and what differences do each make to the requirements for the rest of the installation?
   
2. How do you propose to isolate your supply so that you can connect up your new CU?
   
3. For a circuit to supply a <thing> (doesn't matter what), how would you go about deciding what cable and protective device to use?
   
4. What are the rules concerning cables concealed in walls, partitions and under floors?
   
5. Which circuits must be RCD protected?
   
6. Explain what tests you would carry out on the installation - please cover the sequence you'd do them in and at what point you would energise the installation, and for each test explain what is being measured, why it is important, how you would carry out the test, what sort of results you would expect to get if everything was OK.

 

[Click-Sure]

Good thinking there BAS, I'll jump in with the obvious.

7. Do you understand the implications of Part P, what is covered by it and how you can and connot comply with it.

8. Where cables need to be joined, how should this be done / not be done and in what circumstances are different methods acceptable.

 

[sparkyspike]

9. How do you calculate maximum demand and how can diversity be used?

10. Identifying extraneous conductive parts and what to do about them.

 

[Richard C]

Do I get to be able to self certify if I can answer them all

 

[sparkyspike]

Ok then:

11. What is required in order to self certify? If you are not able to self-certify, then what do you need to do in order to complete the work?

 

[tim west]

12. Can you correctly identify all components and connections of a circuit by method of testing or otherwise? In doing so can you identify or recognise anything wrong or dangerous with the circuit?

 

[DeadJoe]

From a DIYer's point of view, I think these questions may need to be phrased in a way which makes it immediately obvious what is actually being asked. For example:

9. How do you calculate maximum demand and how can diversity be used?

The meaning of 'maximum demand' in this question is pretty self-evident, even if the method of calculating it, and a full knowledge of what factors should be included is not. When someone talks about 'maximum demand' even a very naive DIYer should understand that this is a question which demands that consideration is given to ensuring that the circuits created are designed to be appropriate to the use required, and that they are able to carry the load they will encounter. The very instant I see this question, I realise there are a whole range of issues I would need to consider very carefully and fully understand before I even start to consider doing this sort of work. I also immediately understand that I need to do some maths.

'Diversity' means nothing to me. I can't even begin to answer the question. Therefore, I am not aware of how important this concept might be. That doesn't necessarily mean I don't know what it is, though. I might very well understand the concept, but not have the technical language to describe the concept in this way. And indeed, in this particular case, having looked it up, I believe I did have the concept all along - that designing for 'maximum load' for each circuit might be overkill because there might be any number of reasons why maximum load may never be reached. But as with the case of maximum load, I would have to do a great deal of research to fully understand how to calculate it, and to be honest, I'd probably settle for using the biggest recommended cable size at the lowest recommended length for a circuit and if material costs creep up as a result, then so be it.

Now here's Catch 22. If anything I have said above is obvious nonsense (and it may be) then the question is not helping me understand the enormity of the proposal. I could (but wouldn't), proceed on the basis that I think maximum load is about how much power is drawn as a maximum on each circuit, reduced by a percentage as diversity, all added together.

Basically, I am supporting BAS's contention that:

sometimes there'll be people who'll end up taking advice to either go away and learn a lot more or get an electrician if they can see that there is a lot to know rather than think the advice is aimed at protecting a closed shop.

and:

The questions should all be justifiable, and I think we should avoid a list so long that it looks like deliberate obfuscation.

I think the questions also need to be as simply phrased as possible, and avoid technical terms wherever possible, to ensure they are not seen as an attempt to blind with science.

 

[LiamPope]

The meaning of diversity and exactly how to apply it can be found in about 10 seconds in the OSG/Whitfield/etc, at least one of which any DIYer contemplating a job of this magnitude (me included) should have. Technical terms and nomenclature (Ze, RCBO etc etc) should be used just as they are by pros and in literature. That way the naive DIYer either accepts they are out of their depth and reconsiders, or knows exactly what they have to look up next and learn all about.

That said, I dunno if posing 'quiz' like this is just going to be seen as new posters having to pass an entrance exam in order to be given any advice. Perhaps people should just be told straightforwardly that these jobs are highly involved and that it would be irresponsible for anybody here to hand-walk them through the job, spoon-feeding them information. Instead they need to obtain a certain standard of knowledge in order to fully understand the magnitude of the task. Start with Approved Doc P, OSG, Whitfield etc etc. Say we'll be happy to give some constructive criticism on their proposed schedule of circuits, etc etc.

As I say, I dunno really what's the best way. I just can't help thinking an inquisition would just be an excuse for BAS to shout down and belittle naive DIYers and scare them off without really helping them .

Liam

 

[Taylortwocities]

Allied to question 6.
Advise if you possess, or have access to, a set of calibrated test equipment to enable you to test and certify the installation.

State what test equipment will be required for each test.

(The second part is a basic first year question from my old 2360 course)

 

[dextrous]

I have the answer to all your questions - ignore all professional advice and blithely carry on regardless. Then get a periodical, claiming than some irish bloke who said he was qualified did it, but mysteriously has disappeared off the face of the earth.

 

[LiamPope]

Stuff about testing

Bear in mind that when a DIYer notifies, the LABC are supposed to become responsible for inspection and testing of the work. Whilst for completeness they should definately read up on testing and be aware of what tests are carried out, what the results should be, etc etc, they technically do not require test equipment or the ability to carry out the tests.

Funny you should say that, dextrous. I have one of the crooked LABCs who refuse to carry out the testing. They are inspecting, but on completion just want me to get a PIR! They'll then give me my completion cert.

Liam

 

[dextrous]

Various people have done it, more like.

 

[ban-all-sheds]

Perhaps people should just be told straightforwardly that these jobs are highly involved and that it would be irresponsible for anybody here to hand-walk them through the job, spoon-feeding them information.

Yeah - that always works.

 

[dextrous]

Perhaps people should just be told straightforwardly that these jobs are highly involved and that it would be irresponsible for anybody here to hand-walk them through the job, spoon-feeding them information.

Yeah - that always works.

If it were really true, this forum need not exist

 

[LiamPope]

Sorry I hit submit above rather than preview before I'd written anything. Just checking my modded quote would work...