replacing an MCB?

[Palmerston5]

Okay, so the gist of what you guys are saying is:

1. The MCBs need to be moved to be in the correct order
2. The RCD needs replacing
3. The unterminated wires need to be dealt with in some way.
4. Possibly the CU needs replacing so as to be up-to-date.

I guess it's time for Sparky.

But in the meantime, to go back to my original question, now that you have seen the relevant MCB, are you agreed that it is a ring circuit with too low a breaker - and if so, what is the significance of this? Can I install my new socket whilst waiting for Sparky to come and do his stuff?

 

[Palmerston5]

Oh, and I meant to say, ban-all-sheds, what a fantastic use you have made of my photo. I'm very grateful (and impressed!)

 

[plugwash]

frankly this needs the attention of a sparky and im pretty sure its CU change time

either the earth rod needs to be checked and a CU suitable for a TT (with a 100ma type S rcd as main swtich and a 30ma rcd on all sockets) fitted or the supply needs to be converted to PME and a normal split load CU fitted

 

[dvd freak]

Hello there,

I have floorboarded my loftspace with a view to putting my two PC's up there (outta the way of the missus!) however both PC's have 500 watt supplies in them and with both running together 1000 watts could be consumed if maxed out. I have an old CU unit with only 2-32ma MCB's, 1 15a MCB and a 5a MCB. There are no other MCB's in the unit but there are 3 slots on the buzzbar to take 3 more so all in all it can have no more than 7 MCB's. Pretty dire by todays offerings I think.

The problem I have is that at the moment we are gutting the kitchen and re-plastering it completely (you've guessed it, im a plasterer) she wants 3 double sockets as opposed to the 2 that already reside there so another one adding will do the trick. There is only 1 32a MCB that connects the shower so I would need another to feed the double electric oven on it's own circuit. Also I would like to have a seperate circuit in the loft just in case a socket trips out downstairs, I will not lose data or damage my hard drives. I was thinking of replacing my CU with a newer version that has around 10 MCB's in it but although I have no problem re-wiring the new one in I do have a problem doing this live! I noticed that there is no master switch below/attached to the meter but below the meter there is a box that is fastened with wire, I take it that there is a master fuse in there.

Would it be wrong of me to remove this fuse whilst I replace the new CU?
I notice that there is a warning saying that it should not be tampered with but being on a budget I do not want someone doing what I can do myself and charging me for it (don't get me wrong I would pay if I had to).
I have had a few people tell me it's ok so long as I do the job properly on the other hand I am a little skeptical regarding the legal (if any) implications.

Any advice would be gratefully appreciated

Thanks

Dave

 

[ban-all-sheds]

both PC's have 500 watt supplies in them and with both running together 1000 watts could be consumed if maxed out.

That's only a little over 4A though. Even when you add in monitors, printer(s), scanner(s), speakers etc etc, it'll probably all run off 1 13A socket...

there are 3 slots on the buzzbar

Your busbar shouldn't buzz - if it does there's something wrong...

she wants 3 double sockets as opposed to the 2 that already reside there so another one adding will do the trick.

IIWY I'd consider putting in 6, or 8 or more sockets - can never have too many in a kitchen, all on their own ring, plus possible extra provision for WM/DW/TD...

There is only 1 32a MCB that connects the shower so I would need another to feed the double electric oven on it's own circuit.

Take the opportunity to upgrade the shower circuit to 45/50A, 10mm², and lay in a cooker circuit which could handle an electric hob as well, if required.

Also I would like to have a seperate circuit in the loft just in case a socket trips out downstairs, I will not lose data or damage my hard drives. I was thinking of replacing my CU with a newer version that has around 10 MCB's in it

10 is a bit low, you'll probably find, when you start planning things more closely - 1 or two rings for the kitchen, a non-RCD supply for the fridge/freezer, 3 rings for downstairs/upstairs/loft, oven & shower, and that's eight gone already. Then there are lights, outside (shed/garage/garden), possibly alarm(s), and a couple of spares on each side (RCD/non-RCD)...

Also, do you know what sort of supply you have? If it's a TT earthing arrangement then you'll either need to get that changed, or install the appropriate 100mA-Type-S/30mA split-load board.

but although I have no problem re-wiring the new one in I do have a problem doing this live! I noticed that there is no master switch below/attached to the meter

You could install one of those, too...

but below the meter there is a box that is fastened with wire, I take it that there is a master fuse in there.

If you mean before the meter, and separate from it, just where the service cable comes in, yes.

Would it be wrong of me to remove this fuse whilst I replace the new CU?

Wrong as in not allowed, yes.
Wrong as in not doing it and working live, very much no.

I notice that there is a warning saying that it should not be tampered with but being on a budget I do not want someone doing what I can do myself and charging me for it (don't get me wrong I would pay if I had to).
I have had a few people tell me it's ok so long as I do the job properly on the other hand I am a little skeptical regarding the legal (if any) implications.

It is technically illegal for you to tamper with the fuse, but nobody has ever heard of someone being done for it, unless they've decided, whilst the fuse was out, to connect some of their stuff up to before the meter.

Any advice would be gratefully appreciated

The standard advice is "do not pull the fuse", followed by "but if you do, then do it safely". If you search this forum you'll find lots of tips.

But before you do that, have you approached your DNO? Some are much more cooperative than others and will for free, or for not much money, come and fit an isolator for you. If you tell us where you are, someone might be able to say how friendly your DNO is.

 

[dvd freak]

Well I must admit I did not expect a reply so soon or as in depth....

The advice about my DNO has been taken on board and I gave them a ring (NPOWER) they told me, for £65 they will come out and fit an isolation switch just after the meter so that it is reassuring to know that I will not have to pull the fuse or indeed work live!

I agree about the CU definately, the way you outlined the amount of services that could/would be used from it has raised my brow a little, I can feel the weight of my wallet lightning already..hehe

You mentioned something regarding my type of connection "TT" etc
How do I find out what type I have?

Thank you for the advice it certainly helped me make a few decisions and also enlightened me regarding the layout of the kitchen, she wants low voltage lighting now under the units!

Dave

 

[plugwash]

You mentioned something regarding my type of connection "TT" etc
How do I find out what type I have?

there are 5 earthing systems in existance
IT-neutral totally isolated from earth never seen in normal electricity distribution
TT-supply neutral connected to the body of earth and your earthing system connected seperately to earth via an earth rod
TN-C earth and neutral combined through complete wiring installation. Currently banned in the uk an extremely rare in existing instalations
TN-C-S earth and neutral combined in supply network but split out at the start of your install
TN-S neutral and earth run seperately back to supply transformer

IT and TN-C are so rare that i won't bother discussing them further here

if your earth connects to the suppliers equipment then its a TN-C-S (also known as PME) or TN-S it doesn't (on domestic size installs) make any real difference which. you should run 16mm from the suppliers earth to your earth block 16mm from the earth block to the CU and 10mm (some recs reccomend 16mm but the iee regs only require 10mm) bonding conductors to the incoming gas and water pipes and you should use a normal split load CU

if your earth does not connect to the suppliers wiring at all but does run to a ROD then you have a TT earthing system. this means that you must have EVERYTHING protected by a 100ma type S rcd and you must still have a 30ma non delayed rcd covering ALL sockets

because the time delayed rcds are so expensive it can be cheaper to ask your supplier if they will convert you to TN-C-S than to stick with a TT setup

if you can't find either an earth rod or an earth connectionto the suppliers equipment then you have two choices
1: ask your supplier to convert you to TN-C-S (PME)
2: get an earth rod professionally installed
installing an earth rod is NOT a diy job

 

[Damocles]

Palmerston:
The fact that two cables go into the top of the mcb suggests a ring but does not prove it. It might be two radials (not connected together), or something intended to become a ring which was never completed. You need to check that there is continuity from one cable to the other and not just assume they are connected.

Or possibly they did it like this to deliberately limit maximum current, being as the RCD is only rated at 40A and could be ridiculously overloaded if everything was running at full.

So a think is needed before just swapping it.

 

[dvd freak]

Hope the above works ok.

dvd freak

 

[ban-all-sheds]

Depends what your definition of "works" is. If you meant it to display a placeholder because the image resource can't be found, then it's working just fine. Not sure what the point is though.

Why didn't you click the preview button before you submitted it?

 

[dvd freak]

Sorry about that, I pressed the preview button by my browser locked up so I decided to submit when I visited again once my browser was working (did not want it to lock up again!)

Basically what I wanted to do was submit a photo of my CU to show how it is wired. http://www.infospace.pwp.blueyonder.co.uk

I think that might do the trick! (well I hope so)

dvd freak

 

[plugwash]

had a look does anyone know if current crabtree will fit it

if that idea it also looks to me that wylex nn (wylexes old din rail mount range but still availible from tlc might fit)

 

[dvd freak]

Thanks for taking a look,

My problem is that I want to be able to run several rings including a ring for my power tools in the workshop. I wanted to use this CU in the workshop and put a newer/larger one in the house i.e. at least 10 mcb's.
As can be seen from the picture I only have 4 at the moment with 3 missing but that still only leaves me with 7 max! I know that with the advent of a new kitchen and a new bathroom looming on the horizon the need for extra rings will also increase so what with the workshop too do you think that 7 will be enough?

dvd freak

 

[plugwash]

probablly not and you prbablly want a split load (some cuircuits on rcd and some non-rcd)

id say your best of replacing the CU just got to check out the earthing first (or you could ask the guy when he comes to fit the isolator he should be able to tell you)

 

[dvd freak]

ok I will do that on Wednesday when he arrives to fit it...

Just out of curiosity which CU do you recommend?

I have had people tell me their preferences however and although I know in the end each person has a favourite, is there a good all-rounder that is both reliable, robust and easily configurable?

Thanks for the advanced advice regarding my earthing..

dvd freak