Restricted room in CU for garage circuit and extensions.

[happyhacker]

I have read many of the posts for garages. I want to install a 4mm armoured cable and have the following I need advice on:

1. Firstly on the MCB (bus fed from 100A switch) side of the CU (split unit) I have:

- Door bell
- Cooker
- Central Heating (I assume just the boiler circuit).
- Lights up
- Lights down

On the RCD side I have two ring mains leaving 3 spare positions with two spare 16A switches (MCBs). I will also need a shower RCB here.

2. I am going to bring a 4mm armoured cable in but suspect it will be too bulky to feed into the CU. I will fit a remote CU in the garage for a single ring and lighting there.

Q1. How can I rearrange the CU MCBs to allow a garage feed (assuming I should not use the RCB side)?

Q2. Can I use the spare 16A MCB unused for the garage?

Q3. As I am doing Kitchen work will I need to split its circuit away from the downstairs ring and provide a new one and use the other spare 16A?

Q4. What can I use to join the armoured cable near the CU?

 

[Robgers]

You could consider using a competent electrician.

 

[f42]

No problem feeding your garage from the RCD side, at least your SWA will be protected.

you may want to increase the size of that MCB depending on what your running out in the garage.

you need an adaptable galv box to gland your SWA into before your CU ( which i am assuming is plastic). Remember to earth your glands properly.

 

[flameport]

Q1. How can I rearrange the CU MCBs to allow a garage feed (assuming I should not use the RCB side)?

Assuming no space on the non-RCD side, then remove one of the existing circuits and either combine it with one of the others, or move it the the RCD side.

Q2. Can I use the spare 16A MCB unused for the garage?

Possibly, although this depends on the length of the cable and what loads you expect to have in the garage.

Q3. As I am doing Kitchen work will I need to split its circuit away from the downstairs ring and provide a new one and use the other spare 16A?

Kitchens can have a separate circuit. It isn't a requirement that they do, and it isn't always necessary - it all depends on the loading for the circuit, size of the kitchen and so on.

Q4. What can I use to join the armoured cable near the CU?

Why does it need joining - surely this will be a new cable, which will be purchased in the correct length?

Other things to consider:
This garage circuit, the 'kitchen work' and fitting an electric shower are notifiable, so please read this: //www.diynot.com/wiki/electrics:part_p:diy_electrical_work_and_the_law
If the garage submain will be on a 16A MCB, there is no point in having a ring circuit for the garage sockets.
The garage sockets will require RCD protection, this could be in the house or the garage, not both.
If the submain is connected to the RCD side of the house consumer unit, then a consumer unit in the garage is pointless.

 

[1john]

The 16A garage circuit may as wel be directly wired to all sockets with a switched fused spur at 3A or 5A for the lights.

If you decide to feed the garage from the RCD side of your consumer unit then I would advise some form of double poled isolation near the house consumer unit incase a fault develops and knocks all the power off in your house.

If you alter any of the circuits that are on the non-RCD side they will need to become compliant with the 17th edition, for instance relocating the cooker point or altering light switches.

As mentioned, all of this work is notifiable to the LABC unless you employ someone who can notify themselves.

 

[bernardgreen]

Q4. What can I use to join the armoured cable near the CU?

Untitled

• bernardgreen
• 8 Mar 2009
• 10

Cores from the SWA carried through a hole with a grommet in the top side of the die cast box and taken to the terminals in the CU . Steel wire terminated in the gland at the bottom of the die cast box. No joints in the box.

 

[happyhacker]

Thanks for all your replies. My conclusions so far as follows:

Robgers, I am having the circuits tested by the LA electrician when I have done the work. I have been doing self build for 40 years now and keep informed of the wiring regs.

flameport, I will combine the door bell with the lighting circuit to free up an MCB. I do not want to use the RCB side to avoid it tripping for the sake of the garage. The only question in my mind is do I have to RCB the wiring between the hose and garage CU or is an MCB sufficient?

Current rating remains an issue but I will be having a freezer, lights and power for small DIY tools but no heavy power stuff.

Kitchen is small so I will keep it on the downstairs circuit.

It needs joining surely because I cannot take a heavy cable into the CU. Any ideas?

RCDs in the garage.

I will use a ring in the garage for power.

1John, I will check the regs for the moving of the lighting circuit. Thanks.

bernardgreen, The system in my house says it is a "Protective Multiple Earthed System". Do I need to earth both ends of the sheath? And how does it join to the earth wire?

 

[Adam_151]

It needs joining surely because I cannot take a heavy cable into the CU. Any ideas?

Is your DB metalclad or plastic construction, if the former then gland straight into it, if the latter then metal adaptable box right near it, gland into that take the cores and bedding through into the DB, along with a 4mm earth onto the banjo

Do I need to earth both ends of the sheath? And how does it join to the earth wire?

With an SWA gland, make it off into a metal enclosure and use a banjo tag, lug onto it with a brass bolt, Arguably if using a core as the earth, you only need to earth the armouring at supply end, but you may as well do it both ends as the garage DB is likely (should ideally) be metal anyway. Dont be tempted to just make it off through a stuffing gland with armouring taped up at far end, thats just rough

 

[ban-all-sheds]

Don't be tempted to use banjos either....


//www.diynot.com/forums/viewtopic.php?p=954537#954537

 

[happyhacker]

Very interesting about the earthing. I have a 1970s house that has not been altered in any way except a new CU. In that CU some of the wires have been lengthened using a simple conn. strip join as they would not reach.

Can I fix the armoured cable to my garden wall to save burying it? The wall travels from the house to the garage w/o gaps.

Thanks for the references, very interesting reading. Where can I download copies of the regs?

 

[1john]

cable should be ok clipped to the wall. You have to buy the regs like the rest of us.

 

[ban-all-sheds]

I have been doing self build for 40 years now and keep informed of the wiring regs.

Q1. How can I rearrange the CU MCBs to allow a garage feed (assuming I should not use the RCB side)?

I have been doing self build for 40 years now and keep informed of the wiring regs.

Q2. Can I use the spare 16A MCB unused for the garage?

I have been doing self build for 40 years now and keep informed of the wiring regs.

Q3. As I am doing Kitchen work will I need to split its circuit away from the downstairs ring and provide a new one and use the other spare 16A?

I have been doing self build for 40 years now and keep informed of the wiring regs.

Q4. What can I use to join the armoured cable near the CU?

I have been doing self build for 40 years now and keep informed of the wiring regs.

do I have to RCB the wiring between the hose and garage CU or is an MCB sufficient?

I have been doing self build for 40 years now and keep informed of the wiring regs.

It needs joining surely because I cannot take a heavy cable into the CU. Any ideas?

I have been doing self build for 40 years now and keep informed of the wiring regs.

The system in my house says it is a "Protective Multiple Earthed System". Do I need to earth both ends of the sheath? And how does it join to the earth wire?

I have been doing self build for 40 years now and keep informed of the wiring regs.

Can I fix the armoured cable to my garden wall to save burying it? The wall travels from the house to the garage w/o gaps.

I have been doing self build for 40 years now and keep informed of the wiring regs.

I will check the regs for the moving of the lighting circuit.

Where can I download copies of the regs?

I am having the circuits tested by the LA electrician when I have done the work.

Well let's hope he is happy with what you end up installing on the basis of answers given by people here to only the questions you think you need to ask about.

 

[happyhacker]

I have a full set of requirements from the LA electrician which I need to answer. As follows (for your interest):

The following information should be provided before works commence on the electrical installation:-

1. Design documentation including the following:
(A) Supply characteristics
(B) Installation outline
(C) Distribution design including:-
(i) Protective devices
(ii) Cables
(iii) Voltage drop
(iv) Prospective fault currents
(v) Shock protection
(vi) Selection of protective conductors
(vii) Details of provisions in special locations.
(D) Details of final circuits
(E) Isolation and switching.
2. A suitable plan showing the proposed cable routes.
3. Schematic diagrams showing the number and layout of fixed electrical outlets (lighting and power).

Arrangements should be made with Building Control for the electrical works to be inspected at the first fix stage.

Please note that prior to the installation being tested and inspected at completion the following information must be available.
1. The maximum demand, expressed in amperes, Kw or Kva per phase (after diversity is taken into account)
2. The number and type of live conductors of the source(s) of energy and of the circuits used in the installation.
3. The type of earthing arrangements used by the installation and any facilities provided by the distributor for the user.
4. The nominal voltage(s) and its characteristics including harmonic distortion.
5. The nature of the load current and supply frequency
6. The prospective fault current at the origin of the installation
7. The earth loop impedance (Ze) of that part of the system external to the installation
8. The suitability for the requirements of the installation, including the maximum demand
9. The type and rating of the overcurrent protective device acting at the origin of the installation.
10. Diagrams demonstrating the type and composition of circuits, including points of utilisation, number and size of conductors and type of cable
11. The methods used for compliance with the requirements for basic and fault protection and where appropriate , the conditions required for automatic disconnection
12. The information necessary for the identification of each device performing the functions of protection, isolation and switching and its location
13. Any circuit or equipment vulnerable to a particular test

Circuits should not be energised prior to being subjected to non live test as prescribed in BS7671

Plenty to keep me busy. HOWEVER, I cannot afford to employ an electrician so if I cannot satisfactorily answer these I will continue to use an RCD extension cable to the garage!

 

[1john]

BAS - what are you implying

OP - how much have electricians quoted you for the work vs how much materials are, how long it will take you to do the job and the cost of BC notification??

 

[happyhacker]

Good point I will cost carefully but I guess the garage installation will take 1 day (£250?), the shower 1day (£250?) and the kitchen sockets 1 day (£250?) say £600 for all three as a deal? I could save that! I like the challenge of answering those questions. Sorry "BAS" but that response, if indeed you did all those repeats looses some credibility!