Replacing an old CU with a new one

[Naz1977]

In my area, you pay the fee for a building control notice, and they just pass the fee over to a Leccy company that will come in and just test the installation, so the design will have been done by the buider/diyer, not the tester. I don't know if they are then happy that there is just an electrical safety certificate, and aren't bothered about the design, but it does seem odd.

I was reading down the recent posts, and as I got to the "an electricians job isn't that complicated" I laughed and thought, boy you've just dropped yourself in it. Responses as per expected.

NAZ, read up, check the current regs, have a chat with your electrician, and then come back, and a little of the pique may have subsided by then. I will finish by suggesting you just bed the cables in, as you're never going to have to take them out again if you've done the job properly, and it'll be MCBs on all the circuits although some her would suggests MCBOs on the showers. The RCDs are for earth faults, and not the same as MCB. You do have a lot more reading to do I'm afraid.

THANK you, and much appreciated.

As regards to the comment, I didn't mean that their job isn't complicated, what I meant was the job for my property isn't that complicated. Come on, it is a 2 bed bungalow with couple of lights!

I will also have a chat with the inspector ( independent). I know it says something in the lines of there is a charge of £180 if the installer can't self certify the electrical work and issue the cert. So it maybe that he has an electrician who will do the testing for the £180 ?

I will also get the electrician around to have a chat and see what he says.

The kitchen ring is the latest that was added a while ago ( think about 4 yrs ago) and it is the only circuit that is on a RCBO at the moment. The rest are on MCBs including the current 8Kw shower. There are no RCDs at all in the CU apart from the RCBO.

I just don't know if I should replace the whole CU now or wait until next year when the next floor is in and then I can get more room to work on!

 

[Naz1977]

10 years ago would have been the final revisions of the 16th edition, and while the 17th did introduce various changes, the majority of the basics such as circuit design are exactly the same.


?

I had to take the 17th edition test as well to upgrade from 16th edition to 17th edition for work a long time ago. so it is all up to date currently. Has the onsite guide and the brown book changed at all since then? ( 17th edition ) ?

 

[John D v2.0]

I agree that a domestic electricians job isn't that complicated once you know what you're doing (it's not racing driving or medical research for examples, but by the same token it's not something you can just do without a lot of up front learning), however this is one of those cases where a little knowledge is dangerous because it's easy to think that the job only includes the physical connections. but the testing and design are also necessary. I'd say the testing is much easier than the installation, and the design is extremely easy when dealing with standard domestic circuits although it can get tricky when you go off piste.
I'm sure the hardest part about being an electrician is dealing with customers if I'm honest!

 

[Naz1977]

however this is one of those cases where a little knowledge is dangerous because it's easy to think that the job only includes the physical connections. but the testing and design are also necessary.

Thanks John. Can you please explain a bit more on the above?

If I am to change like for like, then am I not right in saying there is no design involved. I can see the rating of the current MCBs and then I will just change like for like. With the exception of adding a ring to the main circuit instead of using a star layout which it is at the moment!

However, if design is needed, then I am happy to take advice on that.

 

[EFLImpudence]

I know it says something in the lines of there is a charge of £180 if the installer can't self certify the electrical work and issue the cert. So it maybe that he has an electrician who will do the testing for the £180 ?

This is what causes the confusion.

Whoever designs, installs and tests the work should issue an Electrical Certificate. Anyone may do this but not all can.


However, for notifiable work, you need either:

a registered electrician who can self-certify (which really means self-notify), then you will receive a Certificate of Compliance. This is the certificate to which self-certify applies.

or

you notify the Local Authority Building Control before you start the work. They will deem you competent - or not; after which you will receive a Completion Certificate.

I will also get the electrician around to have a chat and see what he says.

Good idea.

The kitchen ring is the latest that was added a while ago ( think about 4 yrs ago) and it is the only circuit that is on a RCBO at the moment.

That is why - because the recent regulations require RCDs on new circuits.

The rest are on MCBs including the current 8Kw shower. There are no RCDs at all in the CU apart from the RCBO.

That is because they were installed before the latest regulations.

I just don't know if I should replace the whole CU now or wait until next year when the next floor is in and then I can get more room to work on!

As you will have to have RCDs on all circuits in your new bathroom, you may as well.

 

[ban-all-sheds]

There are no RCDs at all in the CU apart from the RCBO.

Then if you install any new cables, how do you propose to comply with 522.6.202?

And if you add any new sockets, how do you propose to comply with 411.3.3?

Surely you know about those requirements, if you're putting yourself forward as a competent designer?

 

[ban-all-sheds]

If I am to change like for like, then am I not right in saying there is no design involved.

No - that is yet one more thing you are wrong about.

However, if design is needed, then I am happy to take advice on that.

You've not given any indication so far that you are happy to take advice on that. Quite the opposite in fact.

But we can test your assertion very easily - here is your advice:

Get an electrician - you don't know anywhere near enough.

 

[Naz1977]

This is what causes the confusion.



As you will have to have RCDs on all circuits in your new bathroom, you may as well.

Thanks EFLImpudence. There is no requirement to have a designated RCD for the shower only, am I right as long as there is an RCD protecting that circuit and others for example?

I am thinking about getting a blank 21W CU. Then I can have it wired the way I need it so that I can separate a number of MCBs with a designated RCD for each x number of MCBs. 21W is probably an overkill, but taking into account that an RCD takes 2 spaces, and I think taking future proofing into account, I will need 4 x RCDs, thats 8W gone already and leaves 11 spaces for MCBs.

That way I can also separate the high load items on separate RCDs instead of having them all on only 2 RCDs for example.

so thinking :

RCD1:
1.MCB Electric Shower
2.MCB Shower lights and Fan and Shaver
3.MCB Rest of the ground floor lighting
4.MCB Ground Floor Ring Main

RCD2:
5.MCB Kitchen Ring Main
6.MCB Kitchen Lights
7.MCB First Floor Lighting - Future
8.MCB First Floor Ring Main - Future

RCD3:
9.MCB Cooker
10.MCB Feed to the Consumer unit in the garage - Future

RCBO:
11.Boiler

Obviouly I will discuss this with the leccy as well. However I would appreciate feedback if I am over complicating things ?

 

[Doggit]

Sorry Naz, I tried to suggest you leave it for a bit, but you didn't take the hint, and I'm afraid you're digging yourself an even deeper hole - no offence intended at all because we all have to learn.

No, the design of a domestic installation isn't rocket science, and as long as you follow certain rules such as safe zones etc, and cable size requirements, it can be fairly straightforward, but it's CU that you're showing you're uncertainties in that you are not fully conversant with the differences between and RCD, an MCB and a RCBO, and this is where you need to go and have a chat with someone more qualified than yourself. You've got far too many circuits, and way too many RCDs.

When you come back with a better understanding f the whole installation, and have a few comments from the BCO, then I think you'll get a lot more support. Best of luck Naz

 

[Naz1977]

ok, my understanding is:

RCD: Trips when there is an earth leakge but doesn't trip if there is a live/neutral fault.

MCB: Trips when there is live/neutral fault but not when there is earth leakage

RCBO: Is the combination of both, so that it trips in either case, hence the price difference compared with RCD/MCB

The more circuits you have on an RCD, if it trips then the more devices/circuits will go off line.

Boiler/smoke alarms/burglar alarms need power more than anything else and it is best to have them on their own dedicated RCBO. You can live without lights for couple of days, but can't live without heating for example and ...


Are you saying it is not good to have many RCDs? Isn't it best practice to separate the circuits into zones as far as you can so that in case of failure the least amount of circuits are effected?

Maybe I could get away with RCD3 and then split the 2 MCBs for cooker and outside garage with the other 2 RCDs, but for the cost of £30 or so for an RCD, is it not better to just leave them as separate circuits for failure protection?

1. Shower, has to be separate

2. Bathroom installations : lights, Fan, Shaver Socket, Electric Mirror, Electric towel rail and electric under floor heating ( Future)

3. Lights , Maybe this could be tied with #2 and use the same circuit. But again I quite like the idea of having separate circuits for the bathroom, so that I can then add to the circuit in future, like electric towel warmer or underfloor heating, without having to worry about the MCB tripping. We know the start up current on some devices could trip the MCB if they are turned on at the same time.

4. Again best practice to have a separate ring for each floor. There are about 12-14 sockets on the ground floor.

5. Kitchen ring main: has to be separate

6. Kitchen lights: The current circuit uses the ring main and spurs off that to provide the lighting power. I don't like that. And as the plan is to make the kitchen bigger in future by joining it with the room next to it, I want to keep the light separate from ring main. I could join this with #3.

7. Firstfloor lighting has to be separate

8. First floor Ring main has to be separate

9. Cooker, obviously

10. Feed to consumer unit

11. Boiler

So maybe I could get away with 2 circuits less, but is this really that bad? I can't find anywhere which says how many circuits you are/are not allowed to run off a single domestic CU?

 

[John D v2.0]

Number of circuits is not a problem, but the cost might be, most jobs are done to a price. Although having a crazy amount of cables might be annoying.
You need a minimum number of circuits but not a maximum.
Just to avoid everything going off at once really.

 

[aptsys]

Thanks EFLImpudence. There is no requirement to have a designated RCD for the shower only, am I right as long as there is an RCD protecting that circuit and others for example?

I am thinking about getting a blank 21W CU. Then I can have it wired the way I need it so that I can separate a number of MCBs with a designated RCD for each x number of MCBs. 21W is probably an overkill, but taking into account that an RCD takes 2 spaces, and I think taking future proofing into account, I will need 4 x RCDs, thats 8W gone already and leaves 11 spaces for MCBs.

That way I can also separate the high load items on separate RCDs instead of having them all on only 2 RCDs for example.

so thinking :

RCD1:
1.MCB Electric Shower
2.MCB Shower lights and Fan and Shaver
3.MCB Rest of the ground floor lighting
4.MCB Ground Floor Ring Main

RCD2:
5.MCB Kitchen Ring Main
6.MCB Kitchen Lights
7.MCB First Floor Lighting - Future
8.MCB First Floor Ring Main - Future

RCD3:
9.MCB Cooker
10.MCB Feed to the Consumer unit in the garage - Future

RCBO:
11.Boiler

Obviouly I will discuss this with the leccy as well. However I would appreciate feedback if I am over complicating things ?

I wouldn't split the circuits like this. You could trip the RCD2 because the kettle becomes faulty, but now you've just plunged yourself into darkness because the lights in the kitchen don't work.

There's no issue with the number of RCDs or circuits in general though. Not sure why a poster a few posts above would not be happy with this unless he's the tester working for fixed price.

 

[Naz1977]

So had a leccy around and here is what he said he would do:

RCD1:
Ground Floor lighting - This is all the lighting circuits inc Bathroom light and Kitchen lighting
Upstairs Sockets ( Radial depending on the area, Ring if it is too big). - have since checked roughly and the area will be about 65sqm . So I think this will end up a ring.
Shower
Outside lighting
Cooker



RCD2:
Upstairs Lighting
Downstairs Sockets - Ring
Kitchen Ring Main
shaver socket,under floor heating, Towel Rail and the fan ( Fan will have a 3A Fuse spur on it).
Feed to the garage CU

On its own:
Rcbo Boiler


This is almost the same as I had with the exception of using 2xRCDs and not 3. he said it is ok to use 3 RCDs if I wanted to, but it would cost more. He also said best option would be to use rcbos everywhere but at the cost of £35 a pop, it will be expensive.

He is not happy for me to run the cables and chase and then he terminate and test. It is not worth his time and money as he won't be making any money on it! He is happy for me to chase the walls, but he wants to run the cables and drill the joists even though I am quite capable of making cuts in the joists at the correct space and distance from ends and ...

I have a mate who is a leccy but lives a bit far away, I will see if I can persuade him and get him to come up for the weekend and get drunk

Failing that, what would happen if I do all the work, and don't notify the board. I just then pay for an electrician to come and do a test of the whole electrics, the same as I did before I bought the house. Costed me £150 and he gave me a test certificate. EICR or something like that. That would then prove if my work is ok or not ? Would this be a problem?

 

[EFLImpudence]

Failing that, what would happen if I do all the work, and don't notify the board. I just then pay for an electrician to come and do a test of the whole electrics, the same as I did before I bought the house. Costed me £150 and he gave me a test certificate. EICR or something like that. That would then prove if my work is ok or not ? Would this be a problem?

You would be breaking the law - so, presumably not ok.

 

[Naz1977]

Here is a quote from 'ElectricalSafety.org':

***********************
What if I don’t use a registered electrician?
If you use an installer who is not a registered competent person, he or she must notify the registered third-party certifier within five (5) days of completing the work. The registered third-party certifier will then, subject to the results of the inspection and testing being satisfactory, complete either an Electrical Installation Condition Report (based on the model shown in BS 7671) or one that has been specifically developed for the purposes of Part P and give it to the person ordering the work.

****************************

So lets say I do all the work, but I am not a registered electrician. So I will then get a EICR report done based on my installation and send the report to the council. Why is that breaking the law? Council are already aware of my extension work, so they have been made aware of the changes already,