Adding second CU.

[zemphis]

Hi, i would like to add a small second consumer unit as the original one is old and out of space. The other main reason being that the original CU doesnt have RCD protection.

Recently had an isolator fitted between the meter and the original CU. So im planning to disconnect the supply at the isolator and split this using a henley block. This would then feed both the original CU and the second CU.

From the second CU i need to feed an 8.5kw shower, burglar alarm, doorbell, porch floodlight(150w) and an understairs light(60w).

However, i am a little unsure as to which is the best CU type to purchase. The two main CUs i am considering are:
http://www.screwfix.com/p/mk-sentry-4-way-rcd-garage-consumer-unit/33248?_requestid=619292

The above is described as 4way 2+2 protected. So would this mean there are 4 MCBs and just two of them are RCD protected? 1x6A, 1x16A, 1x40A and the 4th would be?

Or perhaps this one:
http://www.screwfix.com/p/volex-fully-insulated-rcd-board-shower-unit-63a-30ma-rcd/93668

But its described as just a 2-way. So the shower would be connected to the 1x63A and everything else on the 1x50A? This doesnt seem right as i think the 8.5kw shower would need a breaker of 40A max.


Would really appreciate if someone could check over my plan and view both items above. If there is another more suitable type of CU that you could recommend that would be fine too. Thanks

 

[PrenticeBoyofDerry]

How many circuits do you have in the house.
Do away with old board and replace it with one that will service all your circuits.
No need for two CUs.

 

[Adam_151]

I assume you are aware of part P?

The first link (going by the picture as the description seems confused and probably cut and pasted by someone who doesn't quite undertsnad what they are selling)

Is a 4 module enclosure containing and RCD incommer and two outgoing MCB ways, both populated (16 and 6) known as a garage unit by some as the intention is to use it in a garage and feed lights and sockets from it

The second link is similar, 4 module enclosure again with RCD incommer, but populated with a 50A mcb and a blank. Known as a shower unit by some as its intended to be used for a shower.

Neither are suitable for what you want as you need more than two circuits. and by the sounds of it, you could do with some ways that arn't RCD protected.

Are you sure you are competant to do this work

 

[Taylortwocities]

Any of the work you describe is ruled by Building Regulations. You have certain legal obligations if you are to DIY it, or you must use a registered electrician.

See //www.diynot.com/wiki/electrics:part_p:diy_electrical_work_and_the_law for details.

 

[securespark]

I would be tempted to do away with the idea of 2 CU's & fit a new unit to replace the existing gear:

http://www.tlc-direct.co.uk/Products/HGVC714C1.html

Make sure you put the GF sockets & FF lights on one side. The idea being that if the RCD trips, you have not lost both lights & sockets on that floor.

I tend to fit an RCBO on an unprotected busbar just for the GF lights. This way, if the GF lights trip (common), then it doesn't take anything else with it.

Don't forget to upgrade the PEB's to the gas and water pipes, and fit new tails to the new CU.

Also, avoid unsightly installations & IP breaches by mounting the CU on a nice piece of board. One, you get a lovely even surface so no distortion of the CU and two, you can bring all your cables in through the rear, no surface cable entries & sealing to worry about.

DO NOT DO THIS:

 

[wingcoax]

Secure! How long did it take you to do that "job" and what did you charge the customer(mug)?

 

[securespark]

I did not do this job, I only photographed it. Some other guy did it.

 

[EFLImpudence]

Ah! I see what's wrong.

The coloured stripes don't match with the RCDs.

 

[securespark]

The thing that grabs me most when I look at the picture is that the yellow of the RCD test buttons and the yellow of the sticker clash horribly.

 

[ban-all-sheds]

Hi, i would like to add a small second consumer unit as the original one is old and out of space.

• For a circuit to supply a given load, how would you go about deciding what cable and protective device to use? (No, you can't just copy what's there because it's going to become your responsibility and what's there might be wrong.)
  
  
• Do you know which circuits can be ring finals and which cannot, and what the advantages and disadvantages of each are? (No, you can't just copy what's there because it's going to become your responsibility and what's there might be wrong.)
  
  
• How do you calculate maximum demand and how can diversity be used?
  
  
• 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? You cannot assume that what's currently installed is OK, and you need to check it before starting work.
  
  
• Do you understand how the way in which cables are installed affects how much current they can carry? (No, you can't just copy what's there because it's going to become your responsibility and what's there might be wrong.)
  
  
• Where cables need to be joined, how should this be done / not be done and in what circumstances are different methods acceptable?
  
  
• Can you identify extraneous conductive parts, and do you know the requirements for main and supplementary bonding of them?
  
  
• Which circuits should be RCD protected?
  
  
• What about the testing that you should do on your existing installation before you change the CU, if you want to be sure of avoiding grief from new RCDs tripping?
  
  
• And what about the tests you should carry out after the installation? What sequence will you do them in and at what point wil you energise the installation, and for each test do you know what is being measured, why it is important, how you would carry out the test, and with what equipment, and what sort of results you would expect to get if everything was OK?
  

 

[zemphis]

Thanks to everyone for the advice.

I should have mentioned that all the circuits that i listed are already connected to the original CU. So there are no new circuits being added. Just that the original CU is getting messy and tight with extra circuits being added in over a period of time into the existing unit.

The main reason for a second CU is the RCD protection to the shower. So if i were to just move this one shower circuit over to the second CU it would be much simpler. Leaving some room for expansion.

Im still considering this CU: http://www.screwfix.com/p/mk-sentry-4-way-rcd-garage-consumer-unit/33248?_requestid=820439

But its described as 4-way and then it says 40A RCD, 1x16A and 1x6A. This is the part im unsure about. Does it mean one of the circuits is protected by the RCD(40A) and the remaining two(6A,16A) are unprotected? But there must be a fourth.

I believe i need a 40A fuse for the 8.5kw shower. The garage part doesnt matter because it will be fitted next to the original CU under the stairs.

Any further advice appreciated.


PS: securespark, i agree that install shown in the photo is hideous and positively dangerous with half the cables hanging outside the unit.

 

[Taylortwocities]

Im still considering this CU: http://www.screwfix.com/p/mk-sentry-4-way-rcd-garage-consumer-unit/33248?_requestid=820439

But its described as 4-way and then it says 40A RCD, 1x16A and 1x6A. This is the part im unsure about. Does it mean one of the circuits is protected by the RCD(40A) and the remaining two(6A,16A) are unprotected? But there must be a fourth.

I believe i need a 40A fuse for the 8.5kw shower. The garage part doesnt matter because it will be fitted next to the original CU under the stairs.

Any further advice appreciated.
.

You obviously do not know what you are doing.
That CU can only accomodate two circuits. One at 16amp and one at 6amp. Both protected by the RCD. You cannot connect the shower dirctly to the RCD. The 40A part of the RCD refers to the contact rating NOT THE TRIPPING CURRENT. You would have to remove one of the other breakers and replace it with a 40A breaker for the shower.

So, when you ask

Any further advice appreciated.

I would advise that you get an electrician in to replace the existing fuse board mess with a new unit that has space for the additional circuits.

 

[securespark]

That board is very badly described.

It has an RCD incomer, which protects both MCB's, the 16A and the 6A.

It is not suitable for the use you want to put it to.

 

[zemphis]

Surely this one would be ideal then:
http://www.screwfix.com/p/volex-fully-insulated-rcd-board-shower-unit-63a-30ma-rcd/93668

But im convinced it would need a 40A MCB instead of the 50A supplied?



I could hire the help of a sparky. But i think for such a small job i just need a few pointers in the right direction and its diy-able. If i was, for example, wanting to replace the entire CU for another one - then yes i agree totally. I would not attempt that job as it requires far more testing and knowledge.

 

[ban-all-sheds]

Hi, i would like to add a small second consumer unit as the original one is old and out of space.

• For a circuit to supply a given load, how would you go about deciding what cable and protective device to use? (No, you can't just copy what's there because it's going to become your responsibility and what's there might be wrong.)
  
  
• Do you know which circuits can be ring finals and which cannot, and what the advantages and disadvantages of each are? (No, you can't just copy what's there because it's going to become your responsibility and what's there might be wrong.)
  
  
• How do you calculate maximum demand and how can diversity be used?
  
  
• 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? You cannot assume that what's currently installed is OK, and you need to check it before starting work.
  
  
• Do you understand how the way in which cables are installed affects how much current they can carry? (No, you can't just copy what's there because it's going to become your responsibility and what's there might be wrong.)
  
  
• Where cables need to be joined, how should this be done / not be done and in what circumstances are different methods acceptable?
  
  
• Can you identify extraneous conductive parts, and do you know the requirements for main and supplementary bonding of them?
  
  
• Which circuits should be RCD protected?
  
  
• What about the testing that you should do on your existing installation before you change the CU, if you want to be sure of avoiding grief from new RCDs tripping?
  
  
• And what about the tests you should carry out after the installation? What sequence will you do them in and at what point wil you energise the installation, and for each test do you know what is being measured, why it is important, how you would carry out the test, and with what equipment, and what sort of results you would expect to get if everything was OK?