Garage electrics advice

[James2011]

Hi guys

Had a good read of quite a few topics regarding garage electrics and read some good advice, but was hoping you wouldn’t mind having a read of what I had in mind and giving some constructive advice.

First off I now understand that the work is notifiable, what is the procedure for this and what can I expect to encounter? What info do I need for when I ring up? I have a phone number for our council but would like to be a little prepared before I give them a ring.

I would prefer to do the work myself, I am not trained or certified. Could this cause problems in notifying the council bods?


My main consumer board is not RCD protected.

I have a spare slot where I intend to place a 40 amp mcb.

I wish to run 6mm twin and earth round the side/back of the house possible around 10 – 15 meters long, is this thick enough for that amperage?

Catenary wire across to the garage at around a height of 2.5-3 meters (I have read this is ok as long as vehicles aren’t going under, is this correct?) Gap is around 2.5 meters wide.

A 40 amp RCD consumer unit with a 6 amp and 32 amp mcb’s.

Around 5 double sockets, for the odd power sander, pillar drill, also a tumble dryer. Should I make the sockets a ring or radial? Does it matter which? Garage is 5x3m.
Lighting will be 2 or 3 fluorescent tubes with a switch at each door (x2)


Thanks for any advice.

 

[ban-all-sheds]

First off I now understand that the work is notifiable, what is the procedure for this and what can I expect to encounter?

Varies from council to council - there are no rules.

What info do I need for when I ring up?

That depends partly on what they effectively mandate. In theory what you need to do is to tell them how you will ensure that the work you do will comply with P1.

In practice they might make it virtually impossible for you to DIY.

I have a phone number for our council but would like to be a little prepared before I give them a ring.

Have you looked at their website? Notification can't be done by phone anyway.

I would prefer to do the work myself, I am not trained or certified. Could this cause problems in notifying the council bods?

How will you convince them that you know enough to be able to do the work safely?

How will you convince them that you have access to, and know how to use, the equipment needed to test your work?

My main consumer board is not RCD protected.

I have a spare slot where I intend to place a 40 amp mcb.

Not the best design, IMO - better to split the meter tails using service connector blocks and supply the garage separately via a switchfuse.

I wish to run 6mm twin and earth round the side/back of the house possible around 10 – 15 meters long, is this thick enough for that amperage?

It's the wrong sort of cable. You really need to learn more about the regulations. You want to take responsibility for the design and installation of this, so you have to acquire a genuine understanding of all that's involved, you can't ask people here to do it for you.

As for the cable size you should read these:

• http://www.diynot.com/wiki/electrics:mcbtocable
  
  
• http://www.tlc-direct.co.uk/Book/4.3.1.htm
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/cableselection_web.pdf
  
  
• http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
  

Do you have extraneous conductive parts in the garage and a TN-C-S supply?

Should I make the sockets a ring or radial? Does it matter which? Garage is 5x3m.

You should read up on the advantages and disadvantages of each, and make up your own mind, because you are the one who is taking responsibility for the design.

The thing is, installing CUs, outside supplies, submains etc is not a trivial job, and I can assure you that it involves knowing far more than you think it does.

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?

• http://www.diynot.com/wiki/electrics
  
  
• http://www.diynot.com/wiki/electrics:books
  
  
• 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[/list]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.

 

[Chri5]

Doing the work via LBC will cost you £300 plus an external contractors cost to test.

It will also cost you time, as in undertsanding what you will have to do to make sure the job passes.

For a start, a TE cable is not suitable for external runs (not UV protected, will breakdown over a period due to weathering, hasn't got a decent sheath to protect it). TE cannot be supported by catinary wire!

Ideally I'd suggest a sub main feeding directly from a henley block adjacent to your main supply, not fed from your CU.
That will allow the new work to be 17th cert without having to upgrade the CU in house to 17th.

Get a local sparks in to quote, and then discuss what work he will allow you to do to help bring the cost down. Some will tell you no, some will say you can run cables, fit back boxes, supply materials and simply leave terminating, fitting and testing for themselves.

I'd drop the power requirement for the garage to 30 amp, use 6mm SWA and simply avoid running the tumble drier at the same time as you hobby with the power tools.

A 30 amp supply on to a builders / garage CU with RCD or a sweep of RCBO's. 6 amp for lighting and 20 amp radial for sockets.

You might get away with 4mm SWA, but that requires calcs and only a site view would confirm accurate distance for main cable and installation methods used.

I'd also consider use of tray or metal trunking to bridge the area where the main cable 'flies' with it being earthed to the garage supply.

 

[James2011]

Thanks for the feedback.

Chri5, I think I'll try what you say with getting a local guy in and see what he says.

I obviously don't want to risk life and property doing a dodgy job, if I need to pay out, which looks like I will have to then that is the best course of action.

Thanks again for the advice.

Ban-all-sheds

I'll have a read of all your links and reading material, just out of a curiosity on the subject. But think its clear its not safe to Do It Myself. I wouldn't be able to test the work or prove I can do the job to standard.

cheers

 

[SimonH2]

I'd drop the power requirement for the garage to 30 amp, use 6mm SWA and simply avoid running the tumble drier at the same time as you hobby with the power tools.

A 30 amp supply on to a builders / garage CU with RCD or a sweep of RCBO's. 6 amp for lighting and 20 amp radial for sockets.

Hmm, I'd question that - but it depends on what the owner is likely to do in the future. 20A MCB on the sockets, and a 30A (presumably) fuse at the supply end isn't brilliant if he's got a decent welder, compressor, things like that. A mate of mine has a compressor with 2off 3hp motors on it - and when he first got it it was rather prone to blowing fuses*, and when it did it would blow the 30A fuse in the house as well as the garage (both rewireable fuses in a Wylex CU). I think it has 35A fusewire in the house end now for discrimination (30A+5A) - which I think is just within the limits for a 6mm^2 cable clipped direct.

* It was new and the compressors were 'tight', plus it didn't have starting relief valves and if either compressor didn't start sharpish then it would be starting against back pressure before it got going and wouldn't start at all - so blown fuse. It's OK now as it's run in and it's got relief valves that exhaust air until the line is up to a couple of bar pressure during starting - so the first turn or so doesn't load the compressor while it's still running up.

And then there's the welder, and I don't mean one of those cheap ones that would struggle to melt a bean tin

This was all done long before Part P days, I think Ed15 was current back then.