Garage wiring overhaul

[GrumpyMark]

Hi,

Having recently bought my first home, I've spent quite a bit of time browsing useful info on this forum - thanks for all the help so far!

The wiring in the (connected) garage is ancient and has been modified and bodged over many years to the point where it is quite simply, horrifying. It has a 1970 fuse box (5x fuses; 3x 5A and 2x 30A, the two-pin cartridge type with wire in the middle) that is grey and looks like it's been underwater for the last ten years. This is fed from the main house fuse box which is of similar vintage and doesn't appear to be on it's own fuse. The feed cable looks about 10mm2 at a glance. There is a strip light wired from one of the 5A fuses, and a radial circuit going to 3x 2-gang sockets with a mix of white and grey 2.5mm2 (red and black cores in both), and a 1-gang socket on the end. From the 1-gang socket (and this is the best bit), there is a flex cable running out of the back of the garage, through some hosepipe and in to the mostly-disintegrated shed up the garden.

I'd like to replace this lot with a modern consumer unit, wiring and new sockets/switches/light fittings. My plan is to get an IP65 consumer unit with 6A and 16A MCB's for lighting and a radial circuit respectively, run a light switch either end with it's own 4' strip light on 1.5mm2 T+E and four 2-gang sockets on a radial using 2.5mm2 T+E. I'd completely remove the hideous spur to the garden shed.

From the various reading I've done, I realise this is notifiable and would either have to be certificated by a qualified electrician or building control but I'd like to do the work myself to the correct standards.

Does what I've suggested sound reasonable? Can the cable be surface mounted in the garage or would it need to run through conduit? Do I need to consider anything else to make this compliant with the regulations?

Many thanks for any advice,

Mark.

 

[333rocky333]

I dont do domestic work but Im not sure your allowed to fit them consumer units anymore, I am not aware of a metal IP65 one

 

[flameport]

You need to identify where the garage is supplied from the house, ideally it would have it's own circuit.
As it currently doesn't it may be supplied via a 13A fused spur, or far worse, an unfused spur from some other circuit. The condition, type and location of the existing cable must be determined.

A consumer unit in the garage does not need to be IP65, it's somewhat unlikely you can find a metal IP65 type, and a consumer unit isn't even required in the garage anyway.

If the house is as bad as the garage, it would make sense to deal with the house first and the garage much later. If it's unsafe, the garage can be disconnected for now.

 

[securespark]

You need to work out what your loading will be in the garage.

You don't need 1.5 for lighting on a 6A breaker.

I would use PVC conduit at least for the switch / socket drops from ceiling level.

If there are any cable runs near storage areas (in the rafters or near where stuff is stored, hung, etc...) I would protect those as well.

 

[winston1]

You don't need a consumer unit in a connected garage. Run the garage sockets from a 20 amp MCB or RCBO in the main house CU. Run your light via a fused connection unit with a 5 amp fuse using 1.0 mm2 cable. 1.5 is not required or necessary.

 

[ban-all-sheds]

I'd like to do the work myself to the correct standards.

How long do you think/hope/plan that it will be before you are in a position to do that?

Your overall aim is both admirable and achievable, but I fear that you may have underestimated just how much there is to learn.

Does what I've suggested sound reasonable? Can the cable be surface mounted in the garage or would it need to run through conduit? Do I need to consider anything else to make this compliant with the regulations?

And you can't learn like that. Asking questions here can be a useful part of a learning process, but they are not a substitute for proper structured studying. The key term there is "learning process" - you cannot learn all the things you need to know just by asking questions here. It isn't structured enough - it won't provide you with a way to progress where each step builds on what you learned before.

You can't carry out a job of this magnitude by asking whatever random questions happen to occur to you. You've already shown that you have some dodgy misconceptions - what if you get something wrong because you have no idea your knowledge is wrong? What if you miss something because you simply have no idea it even exists, and just don't realise you don't know it?

• [wiki]Electrics%3Aindex[/wiki]
  
  
• [wiki]Electrics%3Abooks[/wiki]
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/electricity.html
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/domesticinstallations.html
  
  
• http://www.tlc-direct.co.uk/Book/1.1.htm

I suggest you get stuck into the last link right away - it won't give you design ideas, and unfortunately it doesn't refer to the current edition of the Wiring Regulations, but it's free, and will still give you a good grounding which you can augment with more up to date publications.

 

[RF Lighting]

I personally think that a separate consumer unit in your garage is the best design.

For a start, it gives you the option to divide up the RCD protection properly. Say a fault occurrs while you're using your circular saw that trips the RCD, you don't want to be plunged in to darkness whilst you're holding a machine with a blade spinning at 1000's of rpm.

It also gives you scope to have a dedicated circuit for a larger piece of equipment such as a welder, a compressor, LINAC, etc.

Don't be fooled by those things advertised as 'garage consumer units' - they really aren't fit for purpose. You want a proper metal clad consumer unit with twice as many ways as you think you'll need.

I fitted a 9 way CU in my garage years ago when I first wired it up and it's now got circuits doubled up as its not big enough for my installation. Whilst I realise my installation is perhaps not your everyday garage installation, it shows how easy it is to under estimate how your installation will evolve over the years.

 

[ericmark]

Set one is to do an electrical installation condition report (EICR) as likely some earth leakage will be happening, and simply swapping the consumer units will just mean the RCD's keep tripping.

So step one is buy/hire a insulation tester and start to test what you have. Likely that will required some training, remember the tester uses 500 volt to test so one does need to know what you are doing before you start.

Once you have completed that EICR, it does not needs to be in a formal document, but you will know what areas need attention first. Then you can start renewing what is required to ensure the RCD is not tripping all the time, once that is complete then you can change the consumer unit.

The idea of swapping consumer units with all RCD protection is all well and good in theroy, you just disconnect any item causing a problem. However that may mean a pair of sockets at the consumer unit and whole of house off line and everything run off extension leads. That's what happened to my son, while bit by bit he re-wired the house and family lived in a caravan in back garden while he did it. OK for him he is an electrician well electrical engineer, but I still feel what he did was both dangerous and silly, better not to have RCD protection for a time while you correct things than have to swap room heater for washing machine, lucky he cooked on gas.

When I did my C&G2391 it was a 12 week night class of 3 hours per week, I would not expect any non electrician to pass, however you would at the end have an idea of how to test stuff in a safe way. When I did it in 2004 it was about £68 but today no longer subsidised so far more expensive. Likely it would be much cheaper to pay some one to do the EICR than to DIY it.

In the main DIY electrics means either safety goes to the wind or the person is a non domestic electrician in the first place. The provision in Part P to allow DIY work is really to allow non domestic electricians to work on their own house. To tick all the boxes to be allowed to do the work yourself you need to satisfy the LABC you have the ability, which in real terms means having written qualifications to show them you have the ability. They may allow you to do the work without the qualifications, but then require you to spend all you saved doing DIY on their fees and paying an electricians they have selected to inspect and test what you have done. And of course if it fails pay for another inspection and test after faults corrected. Swapping odd socket OK but major works today more hassle than it is worth if you are going to jump through the Part P hoops, and if not then the result could be more dangerous than what you started with.

 

[ban-all-sheds]

The provision in Part P to allow DIY work

There is no such "provision" - Part P does not mention DIY work, and it applies equally to any work whatsoever on fixed electrical cables or fixed electrical equipment located on the consumer’s side of the electricity supply meter which operate at low or extra-low voltage and are—

(a) in or attached to a dwelling;
(b) in the common parts of a building serving one or more dwellings, but excluding power supplies to lifts;
(c) in a building that receives its electricity from a source located within or shared with a dwelling; or
(d) in a garden or in or on land associated with a building where the electricity is from a source located within or shared with a dwelling,​

no matter who does the work

the Part P hoops

Not really hoops to jump through. Part P is simply a legal requirement to make reasonable provision in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury.

This is Part P:

 

[winston1]

I personally think that a separate consumer unit in your garage is the best design.

For a start, it gives you the option to divide up the RCD protection properly. Say a fault occurrs while you're using your circular saw that trips the RCD, you don't want to be plunged in to darkness whilst you're holding a machine with a blade spinning at 1000's of rpm.

Indeed you don't. No CU in the garage will protect you from power cuts, so if this is a scenario that concerns you the money is better spent on battery backed emergency lights than an unnecessary CU.

 

[ban-all-sheds]

And no lack of CU in the garage will protect you from power cuts.

But lack of one will mean schlepping back to the house if a device there trips. And might lead to the garage installation or use causing a trip of the house CU.

The presence of a CU in the garage will not introduce new possibilities for inconveniences, but the lack of one will.

Nobody is saying that one is needed, just that it is the best design. Especially when not fed from the house CU.

EM lights probably a good idea no matter how the supply is arranged.

 

[GrumpyMark]

Thanks for all the advice, on reflection I'm going to find an electrician to do an installation report and go from there.

I've checked and as far as I can tell the garage is fed from the back of the 1970s cooker point in the kitchen. I can't see the wire behind the faceplate but I've measured where the cable goes through and it's exactly there.

Since writing the first post I've also discovered that the lounge wall lights are on an unfused spur from a socket. It looks as though the original ceiling rose has been poked into the ceiling and plastered over, with the wire behind the switch taped up with insulation tape...

 

[stem]

You don't need a consumer unit in a connected garage. Run the garage sockets from a 20 amp MCB or RCBO in the main house CU

Judging by the number / rating of the fuses and that it was installed in the 1970's the the CU in the garage is likely the main house CU.

 

[winston1]

And no lack of CU in the garage will protect you from power cuts.

But lack of one will mean schlepping back to the house if a device there trips. And might lead to the garage installation or use causing a trip of the house CU.

The presence of a CU in the garage will not introduce new possibilities for inconveniences, but the lack of one will.

Nobody is saying that one is needed, just that it is the best design. Especially when not fed from the house CU.

EM lights probably a good idea no matter how the supply is arranged.

Would you use the same argument for having a separate CU on every floor of the house, or even every room? The garage is connected to the house, not 60 metres away at the bottom of the garden.

 

[securespark]

I fitted a 9 way CU in my garage years ago when I first wired it up and it's now got circuits doubled up as its not big enough for my installation.

That'll teach you to go mad with MICC...