Screwfix well Electrofix did give me discount, but no longer, there are some things I use Electrofix for like the LAP grid stuff, other things I use Link for which is my local whole sale outlet.
I think DIY is great, but there are safety issues, we have said on a few forums no point having the forum if we simply say get an electrician, however very few DIY people will have access to, or be able to safely use the test equipment to ensure the installation is safe.
Even in England the Part P law says CU fitting has to be registered, in Wales there is very little you can do officially.
OK on the odd time I may do 35 MPH in a 30 MPH limit, but I don't drive at 70 MPH in a 30 MPH limit, and the same applies to electrics, we all break the rules to a small extent, but you really have to consider how to ensure what you have done is safe.
A test set costs around £750 and I assume you would not buy one, so the other way is find some one who has got the equipment and get them to test.
The rub is of course they may tell you that's not acceptable and do nothing, so you need to follow the regulations as close as you can, so anyone inspecting is not going to blow a gasket.
So I would suggest you wait until the pubs open again and try and find a friendly electrician who will either test for you, or lend you a tester.
I have at work been asked questions, and given what I felt was good advice, then latter visited the guy, and realised he had not really related what he had, and as a result the installation was dangerous.
Even my dad's house, we had an electrician change a CU only to find he had not test gear and what he thought was an earth was an earth but was for the old party line phones, not the main electric supply, which had long since been made redundant.
Using a loop impedance tester it became clear there was no earth. But looking at the wires, it was not easy to realise the error.
What had happened I really don't know, there was an earth as when a lot younger I had made a mistake and blown a fuse with a line - earth fault, maybe there were iron water pipes which had been changed to plastic.
As said I went to whole sale outlet, asked for a all RCBO consumer unit with 14 outlets, and was sold what they had in stock and made an error with type of RCBO. If you look at the Screwfix site, as an example part number 3505X rather expensive but only using as an example, spec say 6 kA and curve B, but it does not say if type AC, A, B or F. This link
https://www.electrium.co.uk/media/20200 ... CBO%20(Web).pdf shows it is a type A, but Screwfix are not alone in not actually saying what the type is. The cheaper BG RCBO part number CUCRB32 is type AC on the data sheet
https://www.bgelectrical.uk/public/down ... _RCBOs.pdf but the logos say what type wavy line is type AC and wavy line with line with bumps on underneath is type A [attachment=0]Type A.png[/attachment] but not even sure if you need type A or not?
It seems with CP make type A are £16 so may be worth getting a CU which uses the cheaper options.
I think using the test button is likely good enough with a RCD or RCBO even if it takes 60 seconds instead of 40 mS in the main the RCD trips out before we touch some thing live, mainly due to water ingress. But the problem is the loop impedance, we need it for two reasons, one to show there is an earth, the other to see if 6 kA is enough, many actually read in amps called the prospective short circuit current, and ohms for the earth loop impedance.
It says in the regulations you can get it from enquiry, which means you can ask the DNO what it is at the head, then use a low ohm meter that uses at least 200 mA to calculate what it will be else where.
Why is it important, well the MCB is two devices in one, a thermal trip which is quite slow to act, and a magnetic trip which will work very fast, but with a B type MCB the magnetic part works on between 3 and 5 times the current of the thermal part, so for a B32 MCB the magnetic part needs 160 amp to flow, ohms law 230/160=144Ω add a 5% safety margin and 1.36Ω so with a ring final around centre we want 1.36Ω or less, with a 45A MCB want 0.97Ω or less.
So if the loop impedance is just a little high say 1.2Ω instead of 0.96Ω then with a short circuit it will take minutes to disconnect instead of a fraction of a second, this was not the case with the old fuse, it was only when we moved to the MCB this became a big problem, just a little over and tripping times are much increased.
So if an electrician fits a CU you will get an installation certificate, on that certificate it will show the PSCC and ELI at the consumer unit, so although a multi-meter will not measure using 200 mA it will be in the main good enough for you to test the impedance at any new installation, even simple measuring, we know you can have for example 106 meter of 2.5 mm cable in a ring final and still be within the volt drop limits.
I am not that good at maths, I make errors, so I built a java script program to work it out for me, so I could enter figures where I know the results to see if any errors in program, so reasonable sure now no errors so I can use it to plan an installation.
You get to know when your sailing close to the wind, so most times I install then test, only when I think it may fail do I calculate first, but so much easier now, always seemed to get decimal point wrong with the slide rule, it was OK if I knew answer should be around 1.5 if got 14 or 0.14 I knew I had missed adding or removing a 0, when the calculator came out it was so much easier. But electrical maths includes square roots and imaginary numbers, so needs a good calculator.
I have a copy on the PC of most of the regulations, but have misplaced the book, and so don't have the formula to hand, it was my poor maths which means I only have a foundation degree level 5 not an honours degree. And I will admit there was a lot of luck involved in my passing.
The more one knows, the more one realises how little one knows, my father-in-law had a sign on his desk, these people who think they know it all, are especially annoying to those of us that do.
He would claim light bulbs don't give out light, the suck in the dark, and so when full they go black. We know it is wrong, but try proving it.
Cymru Am Byth